Parsimonious refraction interferometry

KAUST Repository

Hanafy, Sherif; Schuster, Gerard T.

2016-01-01

We present parsimonious refraction interferometry where a densely populated refraction data set can be obtained from just two shot gathers. The assumptions are that the first arrivals are comprised of head waves and direct waves, and a pair of reciprocal shot gathers is recorded over the line of interest. The refraction traveltimes from these reciprocal shot gathers can be picked and decomposed into O(N2) refraction traveltimes generated by N virtual sources, where N is the number of geophones in the 2D survey. This enormous increase in the number of virtual traveltime picks and associated rays, compared to the 2N traveltimes from the two reciprocal shot gathers, allows for increased model resolution and better condition numbers in the normal equations. Also, a reciprocal survey is far less time consuming than a standard refraction survey with a dense distribution of sources.

Refractive error and visual impairment in school children in Northern Ireland.

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O'Donoghue, L; McClelland, J F; Logan, N S; Rudnicka, A R; Owen, C G; Saunders, K J

2010-09-01

To describe the prevalence of refractive error (myopia and hyperopia) and visual impairment in a representative sample of white school children. The Northern Ireland Childhood Errors of Refraction study, a population-based cross-sectional study, examined 661 white 12-13-year-old and 392 white 6-7-year-old children between 2006 and 2008. Procedures included assessment of monocular logarithm of the minimum angle of resolution (logMAR), visual acuity (unaided and presenting) and binocular open-field cycloplegic (1% cyclopentolate) autorefraction. Myopia was defined as -0.50DS or more myopic spherical equivalent refraction (SER) in either eye, hyperopia as > or =+2.00DS SER in either eye if not previously classified as myopic. Visual impairment was defined as >0.30 logMAR units (equivalent to 6/12). Levels of myopia were 2.8% (95% CI 1.3% to 4.3%) in younger and 17.7% (95% CI 13.2% to 22.2%) in older children: corresponding levels of hyperopia were 26% (95% CI 20% to 33%) and 14.7% (95% CI 9.9% to 19.4%). The prevalence of presenting visual impairment in the better eye was 3.6% in 12-13-year-old children compared with 1.5% in 6-7-year-old children. Almost one in four children fails to bring their spectacles to school. This study is the first to provide robust population-based data on the prevalence of refractive error and visual impairment in Northern Irish school children. Strategies to improve compliance with spectacle wear are required.

Refractive surgery for accommodative esotropia: 5-year follow-up.

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Magli, Adriano; Forte, Raimondo; Gallo, Flavio; Carelli, Roberta

2014-02-01

To assess the long-term effectiveness and safety of refractive surgery with LASIK or photorefractive keratectomy (PRK) for treating accommodative esotropia in adults. All patients with accommodative esotropia treated with LASIK or PRK until December 2007 and with a minimum follow-up of 5 years were retrospectively included. LASIK was performed on 44 eyes of 22 patients (12 women, 10 men; mean age: 22.7 ± 2.9 years). Mean postoperative follow-up was 62.1 ± 3.2 months. PRK was performed on 16 eyes of 8 patients (4 women, 4 men; mean age: 23.7 ± 1.7 years). Mean postoperative follow-up was 61.3 ± 2.8 months. At the 5-year follow-up, the mean cycloplegic refraction was more hyperopic in the PRK group (0.3 ± 0.8 vs 0.06 ± 0.3 diopters, P = .01). Correction of esotropia to esophoria or orthotropia was present in 21 patients (95.4%) treated with LASIK and in all patients treated with PRK. Both LASIK and PRK were effective in the long-term reduction of accommodative esotropia. Copyright 2014, SLACK Incorporated.

Análise comparativa entre a refração clínica subjetiva e a automatizada obtida por sensor de frentes de onda Comparative analyses between clinical refraction and automatic refraction obtained through a wave front sensor

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Wilson de Freitas

2007-08-01

Full Text Available OBJETIVO: Avaliar e comparar os resultados obtidos da refração estática clínica com a obtida por sensor de frentes de onda. MÉTODOS: Estudo prospectivo, não seqüencial, de 279 olhos de 147 pacientes. Todos os pacientes foram examinados sob cicloplegia. Primeiro realizamos a refração clínica e a seguir a automatizada por sensor de frentes de onda. Os dados refracionais obtidos foram decompostos para análise vetorial. Foram analisados separadamente os dados de um olho por paciente e dos dois olhos. RESULTADOS: A diferença entre a refração clínica e a automatizada foi de -0,19 DE combinada com -0,06 DC no eixo de 15º para os dados de um olho por paciente e -0,17 DE combinada com -0,05 DC no eixo de 3º para todos os olhos da amostra. CONCLUSÃO: Os dados da refração clínica são comparáveis com os da refração obtida por um sensor de frentes de onda.PURPOSE: To evaluate and compare refractive errors obtained through clinical subjective and automatized wavefront refraction analyses in eyes under cycloplegia. METHODS: Prospective study of 147 patients, 279 eyes, undergoing preoperative examination for refractive surgery. Clinical subjective refraction was performed first followed by wavefront refraction. Results on astigmatism obtained from refraction were decomposed in power vectors for statistical analyses. Data were first analyzed in one eye and then in both eyes. RESULTS: The mean difference between clinical subjective refraction and automatized wavefront refraction on cycloplegic eyes was of -0.19 SD combined with -0.06 CD in the 15º axis for data in one eye, and -0.17 SD combined with -0.05 CD in the 3º axis for data in both eyes of the same patient. CONCLUSION: In the present study clinical subjective refraction and automatized wavefront refraction under cycloplegia had similar numerical values.

Iterative supervirtual refraction interferometry

KAUST Repository

Al-Hagan, Ola

2014-05-02

In refraction tomography, the low signal-to-noise ratio (S/N) can be a major obstacle in picking the first-break arrivals at the far-offset receivers. To increase the S/N, we evaluated iterative supervirtual refraction interferometry (ISVI), which is an extension of the supervirtual refraction interferometry method. In this method, supervirtual traces are computed and then iteratively reused to generate supervirtual traces with a higher S/N. Our empirical results with both synthetic and field data revealed that ISVI can significantly boost up the S/N of far-offset traces. The drawback is that using refraction events from more than one refractor can introduce unacceptable artifacts into the final traveltime versus offset curve. This problem can be avoided by careful windowing of refraction events.

Iterative supervirtual refraction interferometry

KAUST Repository

Al-Hagan, Ola; Hanafy, Sherif M.; Schuster, Gerard T.

2014-01-01

In refraction tomography, the low signal-to-noise ratio (S/N) can be a major obstacle in picking the first-break arrivals at the far-offset receivers. To increase the S/N, we evaluated iterative supervirtual refraction interferometry (ISVI), which is an extension of the supervirtual refraction interferometry method. In this method, supervirtual traces are computed and then iteratively reused to generate supervirtual traces with a higher S/N. Our empirical results with both synthetic and field data revealed that ISVI can significantly boost up the S/N of far-offset traces. The drawback is that using refraction events from more than one refractor can introduce unacceptable artifacts into the final traveltime versus offset curve. This problem can be avoided by careful windowing of refraction events.

Prevalence and association of refractive anisometropia with near work habits among young schoolchildren: The evidence from a population-based study.

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Chia-Wei Lee

Full Text Available Lifestyle behaviour may play a role in refractive error among children, but the association between near work habits and refractive anisometropia remains unclear.We estimated the prevalence of refractive anisometropia and examined its association with near work activities among 23,114 children in the Myopia Investigation Study in Taipei who were grade 2 elementary school students at baseline in 2013 and 2014. Baseline data on demographics, medical history, parental history and near work habits were collected by parent-administered questionnaire survey. Refractive status was determined by cycloplegic autorefraction. Refractive anisometropia was defined as the spherical equivalent difference ≥ 1.0 diopter between eyes.The prevalence of refractive anisometropia was 5.3% (95% confidence interval [CI], 5.0% to 5.6%. The prevalence and severity of refractive anisometropia increased with both myopic and hyperopic refractive error. Multivariate logistic regression analysis revealed that refractive anisometropia was significantly associated with myopia (odds ratio [OR], 2.98; 95% CI, 2.53-3.51, hyperopia (OR, 2.37; 95% CI, 1.98-2.83, degree of astigmatism (OR, 1.005; 95% CI, 1.005-1.006, amblyopia (OR, 2.54; 95% CI, 2.06-3.12, male gender (OR, 0.88; 95% CI, 0.78-0.99 and senior high school level of maternal education (OR, 0.69; 95% CI, 0.52-0.92. Though anisometropic children were more likely to spend more time on near work (crude OR, 1.15; 95% CI, 1.02-1.29 and to have less eye-to-object distance in doing near work (crude OR, 1.15; 95% CI, 1.01-1.30, these associations became insignificant after additional adjustment for ocular, demographic and parental factors.The present study provides large-scale, population-based evidence showing no independent association between refractive anisometropia and near work habits, though myopia is associated with refractive anisometropia.

Understanding refraction contrast using a comparison of absorption and refraction computed tomographic techniques

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Wiebe, S.; Rhoades, G.; Wei, Z.; Rosenberg, A.; Belev, G.; Chapman, D.

2013-05-01

Refraction x-ray contrast is an imaging modality used primarily in a research setting at synchrotron facilities, which have a biomedical imaging research program. The most common method for exploiting refraction contrast is by using a technique called Diffraction Enhanced Imaging (DEI). The DEI apparatus allows the detection of refraction between two materials and produces a unique ''edge enhanced'' contrast appearance, very different from the traditional absorption x-ray imaging used in clinical radiology. In this paper we aim to explain the features of x-ray refraction contrast as a typical clinical radiologist would understand. Then a discussion regarding what needs to be considered in the interpretation of the refraction image takes place. Finally we present a discussion about the limitations of planar refraction imaging and the potential of DEI Computed Tomography. This is an original work that has not been submitted to any other source for publication. The authors have no commercial interests or conflicts of interest to disclose.

Significant Axial Elongation with Minimal Change in Refraction in 3- to 6-Year-Old Chinese Preschoolers: The Shenzhen Kindergarten Eye Study.

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Guo, Xinxing; Fu, Min; Ding, Xiaohu; Morgan, Ian G; Zeng, Yangfa; He, Mingguang

2017-12-01

To document the distribution of ocular biometry and to evaluate its associations with refraction in a group of Chinese preschoolers. Population-based cross-sectional study. A total of 1133 preschoolers 3 to 6 years of age from 8 representative kindergartens. Biometric measurements including axial length (AL), anterior chamber depth (ACD), and corneal radius of curvature (CR) were obtained from partial-coherence laser interferometry (IOL Master; Carl Zeiss Meditec, Oberkochen, Germany) before cycloplegia. Lens power (LP) and AL-to-CR ratio were calculated. Cycloplegic refraction (3 drops of 1% cyclopentolate) was measured using an autorefractor (KR8800; Topcon Corp., Tokyo, Japan), and spherical equivalent refraction (SER) was calculated. Biometric and refractive parameters were assessed as a function of age and gender. Multiple regression analysis was performed to explore the associations between refraction and ocular biometry. Ocular biometric distributions and their relationships to refraction. Among the 1127 children (99.5%) with successful cycloplegic refraction, mean SER was 1.37±0.63 diopters (D). Prevalence of myopia increased from 0% at 3 years of age to 3.7% (95% confidence interval, 1.0%-6.5%) at 6 years of age. Biometric parameters followed Gaussian distributions with means of 22.39±0.68 mm for AL, 7.79±0.25 mm for CR, and 24.61±1.42 D for calculated LP; and non-Gaussian distributions with means of 3.34±0.24 mm for ACD and 2.88±0.06 for AL-to-CR ratio. Axial length, ACD, and AL-to-CR ratio increased from 3 to 6 years of age, CR remained stable, whereas LP declined. Overall, SER declined slightly. For the SER variance, AL explained 18.6% and AL-to-CR ratio explained 39.8%, whereas AL, CR, and LP accounted for 80.0% after adjusting for age and gender. Young Chinese children are predominantly mildly hyperopic, with a low prevalence of myopia by the age of 6 years. An increase of 1 mm in AL was associated with only 0.45 D of myopic change. Decreases in

Relation of anthropometric measurements to ocular biometric changes and refractive error in children with thalassemia.

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Elkitkat, Rania S; El-Shazly, Amany A; Ebeid, Weam M; Deghedy, Marwa R

2018-03-01

To evaluate and correlate anthropometric, biometric, and refractive error changes in thalassemia major (TM). One hundred children with TM and another hundred healthy controls were recruited. Height, weight, body mass index (BMI), and occipitofrontal circumference (OFC) were the anthropometric parameters recorded. Full ophthalmologic examination was performed, including best-corrected visual acuity, cycloplegic refraction, slit-lamp examination, Goldmann applanation tonometry, indirect ophthalmoscopy, keratometry (K readings), and ocular biometry. Compared to controls, children with TM were shorter and lighter, with a smaller BMI (pbiometric data, patients with thalassemia had steeper mean K readings (p = 0.03), shorter axial length (AXL) (p = 0.005), shorter vitreous chamber depth (pbiometric changes (steeper corneas and thicker lenses) to reach emmetropization, with an exaggerated response and subsequent myopic shift. However, growth retardation is not directly related to ocular growth changes, myopic shift, or variations in biometric parameters.

Parsimonious Refraction Interferometry and Tomography

KAUST Repository

Hanafy, Sherif; Schuster, Gerard T.

2017-01-01

We present parsimonious refraction interferometry and tomography where a densely populated refraction data set can be obtained from two reciprocal and several infill shot gathers. The assumptions are that the refraction arrivals are head waves

Crystalline lens power and refractive error.

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Iribarren, Rafael; Morgan, Ian G; Nangia, Vinay; Jonas, Jost B

2012-02-01

To study the relationships between the refractive power of the crystalline lens, overall refractive error of the eye, and degree of nuclear cataract. All phakic participants of the population-based Central India Eye and Medical Study with an age of 50+ years were included. Calculation of the refractive lens power was based on distance noncycloplegic refractive error, corneal refractive power, anterior chamber depth, lens thickness, and axial length according to Bennett's formula. The study included 1885 subjects. Mean refractive lens power was 25.5 ± 3.0 D (range, 13.9-36.6). After adjustment for age and sex, the standardized correlation coefficients (β) of the association with the ocular refractive error were highest for crystalline lens power (β = -0.41; P lens opacity grade (β = -0.42; P lens power (β = -0.95), lower corneal refractive power (β = -0.76), higher lens thickness (β = 0.30), deeper anterior chamber (β = 0.28), and less marked nuclear lens opacity (β = -0.05). Lens thickness was significantly lower in eyes with greater nuclear opacity. Variations in refractive error in adults aged 50+ years were mostly influenced by variations in axial length and in crystalline lens refractive power, followed by variations in corneal refractive power, and, to a minor degree, by variations in lens thickness and anterior chamber depth.

Preliminary study of the correlation between refractive error and corneal refractive power, corneal asphericity in myopic eye

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Qi-Chao Han

2014-05-01

Full Text Available AIM: To investigate the correlation between myopic refractive error and relative factors, including the corneal refractive power, posterior refractive power, axial length, corneal asphericity coefficient Q value, central cornea thickness(CCTand intraocular pressure(IOP. METHODS:According to the degree of myopia measured by subjective refraction, 138 myopia patients were divided into three subgroups: mild group(-1.00D--3.00D, moderate group(-3.25D--6.00D, high group(>6.00D. The Pentacam anterior segment tomographer(Germany, Oculus Companywas used to measure the corneal refractive power, posterior refractive power, and corneal asphericity in the right eye. IOP, CCT and axial length were measured by a non-contact tonometer and A-scan ultrasonic, respectively. The data was analyzed with a Pearson correlation analysis and one-way ANOVA. RESULTS: The myopic refractive error was negatively correlated with the axial length(r=-0.682, Pr=0.009, P=0.925. The axial length was negatively correlated with corneal refractive power(r=-0.554, Pr=0.674, Pr=-0.375, P=0.01. There was no significantly correlation between the myopic refractive error and CCT, IOP(r=-0.138, P=0.141; r=-0.121, P=0.157. CONCLUSION:The corneal refractive power plays the role of emmetropization during the development of myopia. There is clinic significance for the correlation between Q value and refractive error, IOP to guide the corneal refractive surgery.

Association between Refractive Errors and Ocular Biometry in Iranian Adults

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Hashemi, Hassan; Khabazkhoob, Mehdi; Emamian, Mohammad Hassan; Shariati, Mohammad; Miraftab, Mohammad; Yekta, Abbasali; Ostadimoghaddam, Hadi; Fotouhi, Akbar

2015-01-01

Purpose: To investigate the association between ocular biometrics such as axial length (AL), anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD) and corneal power (CP) with different refractive errors. Methods: In a cross-sectional study on the 40 to 64-year-old population of Shahroud, random cluster sampling was performed. Ocular biometrics were measured using the Allegro Biograph (WaveLight AG, Erlangen, Germany) for all participants. Refractive errors were determined using cycloplegic refraction. Results: In the first model, the strongest correlations were found between spherical equivalent with axial length and corneal power. Spherical equivalent was strongly correlated with axial length in high myopic and high hyperopic cases, and with corneal power in high hyperopic cases; 69.5% of variability in spherical equivalent was attributed to changes in these variables. In the second model, the correlations between vitreous chamber depth and corneal power with spherical equivalent were stronger in myopes than hyperopes, while the correlations between lens thickness and anterior chamber depth with spherical equivalent were stronger in hyperopic cases than myopic ones. In the third model, anterior chamber depth + lens thickness correlated with spherical equivalent only in moderate and severe cases of hyperopia, and this index was not correlated with spherical equivalent in moderate to severe myopia. Conclusion: In individuals aged 40-64 years, corneal power and axial length make the greatest contribution to spherical equivalent in high hyperopia and high myopia. Anterior segment biometric components have a more important role in hyperopia than myopia. PMID:26730304

Deviations of Lambert-Beer???s law affect corneal refractive parameters after refractive surgery

OpenAIRE

Jim??nez Cuesta, Jos?? Ram??n; Rodr??guez-Mar??n, Francisco; Gonz??lez Anera, Rosario; Jim??nez del Barco Jaldo, Luis Miguel

2006-01-01

We calculate whether deviations of Lambert-Beer???s law, which regulates depth ablation during corneal ablation, significantly influence corneal refractive parameters after refractive surgery and whether they influence visual performance. For this, we compute a point-to-point correction on the cornea while assuming a non-linear (including a quadratic term) fit for depth ablation. Post-surgical equations for refractive parameters using a non-linear fit show significant differences with respect...

Questionnaires for Measuring Refractive Surgery Outcomes.

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Kandel, Himal; Khadka, Jyoti; Lundström, Mats; Goggin, Michael; Pesudovs, Konrad

2017-06-01

To identify the questionnaires used to assess refractive surgery outcomes, assess the available questionnaires in regard to their psychometric properties, validity, and reliability, and evaluate the performance of the available questionnaires in measuring refractive surgery outcomes. An extensive literature search was done on PubMed, MEDLINE, Scopus, CINAHL, Cochrane, and Web of Science databases to identify articles that described or used at least one questionnaire to assess refractive surgery outcomes. The information on content quality, validity, reliability, responsiveness, and psychometric properties was extracted and analyzed based on an extensive set of quality criteria. Eighty-one articles describing 27 questionnaires (12 refractive error-specific, including 4 refractive surgery-specific, 7 vision-but-non-refractive, and 8 generic) were included in the review. Most articles (56, 69.1%) described refractive error-specific questionnaires. The Quality of Life Impact of Refractive Correction (QIRC), the Quality of Vision (QoV), and the Near Activity Visual Questionnaire (NAVQ) were originally constructed using Rasch analysis; others were developed using the Classical Test Theory. The National Eye Institute Refractive Quality of Life questionnaire was the most frequently used questionnaire, but it does not provide a valid measurement. The QoV, QIRC, and NAVQ are the three best existing questionnaires to assess visual symptoms, quality of life, and activity limitations, respectively. This review identified three superior quality questionnaires for measuring different aspects of quality of life in refractive surgery. Clinicians and researchers should choose a questionnaire based on the concept being measured with superior psychometric properties. [J Refract Surg. 2017;33(6):416-424.]. Copyright 2017, SLACK Incorporated.

Influence of refraction index strength on the light propagation in dielectrics material with periodic refraction index

International Nuclear Information System (INIS)

Hidayat, Arif; Latifah, Eny; Kurniati, Diana; Wisodo, Hari

2016-01-01

This study investigated the influence of refraction index strength on the light propagation in refraction index-varied dielectric material. This dielectric material served as photonic lattice. The behavior of light propagation influenced by variation of refraction index in photonic lattice was investigated. Modes of the guiding light were determined numerically using squared-operator iteration method. It was found that the greater the strength of refraction index, the smaller the guiding modes.

Correction of refractive errors

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Vladimir Pfeifer

2005-10-01

Full Text Available Background: Spectacles and contact lenses are the most frequently used, the safest and the cheapest way to correct refractive errors. The development of keratorefractive surgery has brought new opportunities for correction of refractive errors in patients who have the need to be less dependent of spectacles or contact lenses. Until recently, RK was the most commonly performed refractive procedure for nearsighted patients.Conclusions: The introduction of excimer laser in refractive surgery has given the new opportunities of remodelling the cornea. The laser energy can be delivered on the stromal surface like in PRK or deeper on the corneal stroma by means of lamellar surgery. In LASIK flap is created with microkeratome in LASEK with ethanol and in epi-LASIK the ultra thin flap is created mechanically.

Parsimonious Refraction Interferometry and Tomography

KAUST Repository

Hanafy, Sherif

2017-02-04

We present parsimonious refraction interferometry and tomography where a densely populated refraction data set can be obtained from two reciprocal and several infill shot gathers. The assumptions are that the refraction arrivals are head waves, and a pair of reciprocal shot gathers and several infill shot gathers are recorded over the line of interest. Refraction traveltimes from these shot gathers are picked and spawned into O(N2) virtual refraction traveltimes generated by N virtual sources, where N is the number of geophones in the 2D survey. The virtual traveltimes can be inverted to give the velocity tomogram. This enormous increase in the number of traveltime picks and associated rays, compared to the many fewer traveltimes from the reciprocal and infill shot gathers, allows for increased model resolution and a better condition number with the system of normal equations. A significant benefit is that the parsimonious survey and the associated traveltime picking is far less time consuming than that for a standard refraction survey with a dense distribution of sources.

Refractive errors in students from Middle Eastern backgrounds living and undertaking schooling in Australia.

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Azizoglu, Serap; Junghans, Barbara M; Barutchu, Ayla; Crewther, Sheila G

2011-01-01

  Environmental factors associated with schooling systems in various countries have been implicated in the rising prevalence of myopia, making the comparison of prevalence of refractive errors in migrant populations of interest. This study aims to determine the prevalence of refractive errors in children of Middle Eastern descent, raised and living in urban Australia but actively maintaining strong ties to their ethnic culture, and to compare them with those in the Middle East where myopia prevalence is generally low.   A total of 354 out of a possible 384 late primary/early secondary schoolchildren attending a private school attracting children of Middle Eastern background in Melbourne were assessed for refractive error and visual acuity. A Shin Nippon open-field NVision-K5001 autorefractor was used to carry out non-cycloplegic autorefraction while viewing a distant target. For statistical analyses students were divided into three age groups: 10-11 years (n = 93); 12-13 years (n = 158); and 14-15 years (n = 102).   All children were bilingual and classified as of Middle Eastern (96.3 per cent) or Egyptian (3.7 per cent) origin. Ages ranged from 10 to 15 years, with a mean of 13.17 ± 0.8 (SEM) years. Mean spherical equivalent refraction (SER) for the right eye was +0.09 ± 0.07 D (SEM) with a range from -7.77 D to +5.85 D. The prevalence of myopia, defined as a spherical equivalent refraction 0.50 D or more of myopia, was 14.7 per cent. The prevalence of hyperopia, defined as a spherical equivalent refraction of +0.75 D or greater, was 16.4 per cent, while hyperopia of +1.50 D or greater was 5.4 per cent. A significant difference in SER was seen as a function of age; however, no significant gender difference was seen.   This is the first study to report the prevalence of refractive errors for second-generation Australian schoolchildren coming from a predominantly Lebanese Middle Eastern Arabic background, who endeavour to maintain their ethnic ties. The

Peripheral refraction in normal infant rhesus monkeys

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Hung, Li-Fang; Ramamirtham, Ramkumar; Huang, Juan; Qiao-Grider, Ying; Smith, Earl L.

2008-01-01

Purpose To characterize peripheral refractions in infant monkeys. Methods Cross-sectional data for horizontal refractions were obtained from 58 normal rhesus monkeys at 3 weeks of age. Longitudinal data were obtained for both the vertical and horizontal meridians from 17 monkeys. Refractive errors were measured by retinoscopy along the pupillary axis and at eccentricities of 15, 30, and 45 degrees. Axial dimensions and corneal power were measured by ultrasonography and keratometry, respectively. Results In infant monkeys, the degree of radial astigmatism increased symmetrically with eccentricity in all meridians. There were, however, initial nasal-temporal and superior-inferior asymmetries in the spherical-equivalent refractive errors. Specifically, the refractions in the temporal and superior fields were similar to the central ametropia, but the refractions in the nasal and inferior fields were more myopic than the central ametropia and the relative nasal field myopia increased with the degree of central hyperopia. With age, the degree of radial astigmatism decreased in all meridians and the refractions became more symmetrical along both the horizontal and vertical meridians; small degrees of relative myopia were evident in all fields. Conclusions As in adult humans, refractive error varied as a function of eccentricity in infant monkeys and the pattern of peripheral refraction varied with the central refractive error. With age, emmetropization occurred for both central and peripheral refractive errors resulting in similar refractions across the central 45 degrees of the visual field, which may reflect the actions of vision-dependent, growth-control mechanisms operating over a wide area of the posterior globe. PMID:18487366

Validity of automated refraction after segmented refractive multifocal intraocular lens implantation.

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Albarrán-Diego, César; Muñoz, Gonzalo; Rohrweck, Stephanie; García-Lázaro, Santiago; Albero, José Ricardo

2017-01-01

To evaluate the clinical utility of automated refraction (AR) and keratometry (KR) compared with subjective or manifest refraction (MR) after cataract or refractive lens exchange surgery with implantation of Lentis Mplus X (Oculentis GmbH) refractive multifocal intraocular lens (IOL). Eighty-six eyes implanted with the Lentis Mplus X multifocal IOL were included. MR was performed in all patients followed by three consecutive AR measurements using the Topcon KR-8000 autorefractor. Assessment of repeatability of consecutive AR before and after dilation with phenylephrine 10%, and comparison of the AR and KR with MR using vector analysis were performed at 3mo follow-up. Analysis showed excellent repeatability of the AR measurements. Linear regression of AR versus MR showed good correlation for sphere and spherical equivalent, whereas the correlation for astigmatism was low. The mean difference AR-MR was -1.28±0.29 diopters (D) for sphere. Astigmatism showed better correlation between KR and MR. We suggest AR sphere plus 1.25 D and the KR cylinder as the starting point for MR in eyes with a Lentis Mplus X multifocal IOL. If AR measurements are equal to MR, decentration of the IOL should be suspected.

Identifying Children at Risk of High Myopia Using Population Centile Curves of Refraction.

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Yanxian Chen

Full Text Available To construct reference centile curves of refraction based on population-based data as an age-specific severity scale to evaluate their efficacy as a tool for identifying children at risk of developing high myopia in a longitudinal study.Data of 4218 children aged 5-15 years from the Guangzhou Refractive Error Study in Children (RESC study, and 354 first-born twins from the Guangzhou Twin Eye Study (GTES with annual visit were included in the analysis. Reference centile curves for refraction were constructed using a quantile regression model based on the cycloplegic refraction data from the RESC. The risk of developing high myopia (spherical equivalent ≤ -6 diopters [D] was evaluated as a diagnostic test using the twin follow-up data.The centile curves suggested that the 3rd, 5th, and 10th percentile decreased from -0.25 D, 0.00 D and 0.25 D in 5 year-olds to -6.00 D, -5.65D and -4.63 D in 15 year-olds in the population-based data from RESC. In the GTES cohort, the 5th centile showed the most effective diagnostic value with a sensitivity of 92.9%, a specificity of 97.9% and a positive predictive value (PPV of 65.0% in predicting high myopia onset (≤-6.00D before the age of 15 years. The PPV was highest (87.5% in 3rd centile but with only 50.0% sensitivity. The Mathew's correlation coefficient of 5th centile in predicting myopia of -6.0D/-5.0D/-4.0D by age of 15 was 0.77/0.51/0.30 respectively.Reference centile curves provide an age-specific estimation on a severity scale of refractive error in school-aged children. Children located under lower percentiles at young age were more likely to have high myopia at 15 years or probably in adulthood.

Emmetropisation and the aetiology of refractive errors

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Flitcroft, D I

2014-01-01

The distribution of human refractive errors displays features that are not commonly seen in other biological variables. Compared with the more typical Gaussian distribution, adult refraction within a population typically has a negative skew and increased kurtosis (ie is leptokurtotic). This distribution arises from two apparently conflicting tendencies, first, the existence of a mechanism to control eye growth during infancy so as to bring refraction towards emmetropia/low hyperopia (ie emmetropisation) and second, the tendency of many human populations to develop myopia during later childhood and into adulthood. The distribution of refraction therefore changes significantly with age. Analysis of the processes involved in shaping refractive development allows for the creation of a life course model of refractive development. Monte Carlo simulations based on such a model can recreate the variation of refractive distributions seen from birth to adulthood and the impact of increasing myopia prevalence on refractive error distributions in Asia. PMID:24406411

Atmospheric refraction : a history

NARCIS (Netherlands)

Lehn, WH; van der Werf, S

2005-01-01

We trace the history of atmospheric refraction from the ancient Greeks up to the time of Kepler. The concept that the atmosphere could refract light entered Western science in the second century B.C. Ptolemy, 300 years later, produced the first clearly defined atmospheric model, containing air of

Validity of automated refraction after segmented refractive multifocal intraocular lens implantation

Directory of Open Access Journals (Sweden)

César Albarrán-Diego

2017-11-01

Full Text Available AIM: To evaluate the clinical utility of automated refraction (AR and keratometry (KR compared with subjective or manifest refraction (MR after cataract or refractive lens exchange surgery with implantation of Lentis Mplus X (Oculentis GmbH refractive multifocal intraocular lens (IOL. METHODS: Eighty-six eyes implanted with the Lentis Mplus X multifocal IOL were included. MR was performed in all patients followed by three consecutive AR measurements using the Topcon KR-8000 autorefractor. Assessment of repeatability of consecutive AR before and after dilation with phenylephrine 10%, and comparison of the AR and KR with MR using vector analysis were performed at 3mo follow-up. RESULTS: Analysis showed excellent repeatability of the AR measurements. Linear regression of AR versus MR showed good correlation for sphere and spherical equivalent, whereas the correlation for astigmatism was low. The mean difference AR-MR was -1.28±0.29 diopters (D for sphere. Astigmatism showed better correlation between KR and MR. CONCLUSION: We suggest AR sphere plus 1.25 D and the KR cylinder as the starting point for MR in eyes with a Lentis Mplus X multifocal IOL. If AR measurements are equal to MR, decentration of the IOL should be suspected.

Prevalence and associations of anisometropia with spherical ametropia, cylindrical power, age, and sex in refractive surgery candidates.

Science.gov (United States)

Linke, Stephan J; Richard, Gisbert; Katz, Toam

2011-09-29

To analyze the prevalence and associations of anisometropia with spherical ametropia, astigmatism, age, and sex in a refractive surgery population. Medical records of 27,070 eyes of 13,535 refractive surgery candidates were reviewed. Anisometropia, defined as the absolute difference in mean spherical equivalent powers between right and left eyes, was analyzed for subjective (A(subj)) and cycloplegic refraction (A(cycl)). Correlations between anisometropia (>1 diopter) and spherical ametropia, cylindrical power, age, and sex, were analyzed using χ² and nonparametric Kruskal-Wallis or Mann-Whitney tests and binomial logistic regression analyses. Power vector analysis was applied for further analysis of cylindrical power. Prevalence of A(subj) was 18.5% and of A(cycl) was 19.3%. In hyperopes, logistic regression analysis revealed that only spherical refractive error (odds ratio [OR], 0.72) and age (OR, 0.97) were independently associated with anisometropia. A(subj) decreased with increasing spherical ametropia and advancing age. Cylindrical power and sex did not significantly affect A(subj). In myopes all explanatory variables (spherical power OR, 0.93; cylindrical power OR, 0.75; age OR, 1.02; sex OR, 0.8) were independently associated with anisometropia. Cylindrical power was most strongly associated with anisometropia. Advancing age and increasing spherical/cylindrical power correlated positively with increasing anisometropia in myopic subjects. Female sex was more closely associated with anisometropia. This large-scale retrospective analysis confirmed an independent association between anisometropia and both spherical ametropia and age in refractive surgery candidates. Notably, an inverse relationship between these parameters in hyperopes was observed. Cylindrical power and female sex were independently associated with anisometropia in myopes.

The uncorrected refractive error challenge

Directory of Open Access Journals (Sweden)

Kovin Naidoo

2016-11-01

Full Text Available Refractive error affects people of all ages, socio-economic status and ethnic groups. The most recent statistics estimate that, worldwide, 32.4 million people are blind and 191 million people have vision impairment. Vision impairment has been defined based on distance visual acuity only, and uncorrected distance refractive error (mainly myopia is the single biggest cause of worldwide vision impairment. However, when we also consider near visual impairment, it is clear that even more people are affected. From research it was estimated that the number of people with vision impairment due to uncorrected distance refractive error was 107.8 million,1 and the number of people affected by uncorrected near refractive error was 517 million, giving a total of 624.8 million people.

EDITORIAL: Sensitive structures: refractive indices in nanotechnology Sensitive structures: refractive indices in nanotechnology

Science.gov (United States)

Demming, Anna

2012-12-01

Refractive index effects using nanoscale systems are frequently applied in new imaging, sensing and even visibility cloaking technology. In this issue, researchers in Japan use simulations and experiments to describe the confinement of optical vortices in nanoscale fin structures and the sensitivity of these systems to the refractive index of the surrounding media [1]. The effects of refraction as light rays pass between different media were recorded as long ago as the first century AD, by Ptolemy [2]. Over the following centuries the phenomena inspired Ibn Sahl in 984 [3], Thomas Harriot in 1602 [4], Willebrord Snellius in 1621 [5] and Rene Descartes in 1637 [6] to independently derive the more accurate and elegant equation for refraction so familiar to us today. Recent studies of the interactions between light and matter continue to reveal a wealth of phenomena that originate in the effects of the refractive indices of materials. Nanostructures can be used to manipulate conditions that affect the refractive indices of materials, such as temperature. A E Aliev et al at the University of Texas reported a striking demonstration of temperature-dependent refractive index effects using a free-standing, highly aligned carbon nanotube aerogel sheet [7]. They used the extremely low thermal capacitance and high heat transfer ability of transparent carbon nanotube sheets to enable high-frequency modulation of the sheet temperature over an enormous temperature range. The resulting sharp, rapidly changing gradient of the refractive index in the surrounding liquid or gas makes objects seem to disappear and can be used for visibility cloaking. Light-matter interaction resonances, where light is confined at the nanoscale, can be extremely sensitive to changes in the refractive index of the surrounding media [8], even allowing single-molecule detection [9]. Plasmons, the collective oscillations of electrons in response to incident light, are a typical example. Researchers at Rice

Assessment of multifocal contact lens over-refraction using an infrared, open-field autorefractor: A preliminary study.

Science.gov (United States)

Giner, Anna; Aldaba, Mikel; Arjona, Montserrat; Vilaseca, Meritxell; Pujol, Jaume

2015-10-01

To evaluate the usefulness of an infrared open-field autorefractor as a predictor of the refractive error when fitting multifocal contact lenses (MCL). Objective and subjective measurements of the non-cycloplegic distance refractive error were compared in patients wearing MCL. We used the Grand Seiko WAM-5500 autorefractor for the objective measurements. Three commercially available MCL were tested. Twenty-one eyes of sixteen healthy adults were included in the study. Over-refraction was evaluated in terms of spherical equivalent (SE) and astigmatic vectors (J0 and J45). The mean difference±SD of each parameter was calculated. The Kolmogorov-Smirnov test was used to verify the normal distribution. Pearson's correlation, Bland and Altman plot and paired sample t test were used to compare the results obtained with both methods. The mean difference between objective and subjective results of the SE over-refraction was 0.13±0.42D; for astigmatic vectors J0 and J45 were 0.03±0.32D and -0.00±0.17D, respectively. The Kolmogorov-Smirnov test showed a normal distribution for all parameters. The highest Pearson's correlation coefficients were obtained for the SE with values of 0.98 without MCL and 0.97 with MCL. The lowest were obtained for J45 with values of 0.65 without MCL and 0.75 with MCL. Significant correlations were obtained for each parameter. The paired sample t test failed to show significant differences in analyzed parameters except for J0 without MCL. The Grand Seiko WAM-5500 can be used as a screening method of over-refraction in the clinical fitting of MCL. Copyright © 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

Investigating the relationship between foveal morphology and refractive error in a population with infantile nystagmus syndrome.

Science.gov (United States)

Healey, Natasha; McLoone, Eibhlin; Mahon, Gerald; Jackson, A Jonathan; Saunders, Kathryn J; McClelland, Julie F

2013-04-26

We explored associations between refractive error and foveal hypoplasia in infantile nystagmus syndrome (INS). We recruited 50 participants with INS (albinism n = 33, nonalbinism infantile nystagmus [NAIN] n = 17) aged 4 to 48 years. Cycloplegic refractive error and logMAR acuity were obtained. Spherical equivalent (SER), most ametropic meridian (MAM) refractive error, and better eye acuity (VA) were used for analyses. High resolution spectral-domain optical coherence tomography (SD-OCT) was used to obtain foveal scans, which were graded using the Foveal Hypoplasia Grading Scale. Associations between grades of severity of foveal hypoplasia, and refractive error and VA were explored. Participants with more severe foveal hypoplasia had significantly higher MAMs and SERs (Kruskal-Wallis H test P = 0.005 and P = 0.008, respectively). There were no statistically significant associations between foveal hypoplasia and cylindrical refractive error (Kruskal-Wallis H test P = 0.144). Analyses demonstrated significant differences between participants with albinism or NAIN in terms of SER and MAM (Mann-Whitney U test P = 0.001). There were no statistically significant differences between astigmatic errors between participants with albinism and NAIN. Controlling for the effects of albinism, results demonstrated no significant associations between SER, and MAM and foveal hypoplasia (partial correlation P > 0.05). Poorer visual acuity was associated statistically significantly with more severe foveal hypoplasia (Kruskal-Wallis H test P = 0.001) and with a diagnosis of albinism (Mann-Whitney U test P = 0.001). Increasing severity of foveal hypoplasia is associated with poorer VA, reflecting reduced cone density in INS. Individuals with INS also demonstrate a significant association between more severe foveal hypoplasia and increasing hyperopia. However, in the absence of albinism, there is no significant relation between refractive outcome and degree of foveal hypoplasia

Negative refraction angular characterization in one-dimensional photonic crystals.

Directory of Open Access Journals (Sweden)

Jesus Eduardo Lugo

2011-04-01

Full Text Available Photonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity developed here. We also analytically derived the negative refraction correctness condition that gives the angular region where negative refraction occurs.By using standard photonic techniques we experimentally determined the relationship between incidence and negative refraction angles and found the negative refraction range by applying the correctness condition. In order to compare both theories with experimental results an output refraction correction was utilized. The correction uses Snell's law and an effective refractive index based on two effective dielectric constants. We found good agreement between experiment and both theories in the negative refraction zone.Since both theories and the experimental observations agreed well in the negative refraction region, we can use both negative refraction theories plus the output correction to predict negative refraction angles. This can be very useful from a practical point of view for space filtering applications such as a photonic demultiplexer or for sensing applications.

Negative refraction angular characterization in one-dimensional photonic crystals.

Science.gov (United States)

Lugo, Jesus Eduardo; Doti, Rafael; Faubert, Jocelyn

2011-04-06

Photonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity developed here. We also analytically derived the negative refraction correctness condition that gives the angular region where negative refraction occurs. By using standard photonic techniques we experimentally determined the relationship between incidence and negative refraction angles and found the negative refraction range by applying the correctness condition. In order to compare both theories with experimental results an output refraction correction was utilized. The correction uses Snell's law and an effective refractive index based on two effective dielectric constants. We found good agreement between experiment and both theories in the negative refraction zone. Since both theories and the experimental observations agreed well in the negative refraction region, we can use both negative refraction theories plus the output correction to predict negative refraction angles. This can be very useful from a practical point of view for space filtering applications such as a photonic demultiplexer or for sensing applications.

Wave-vector and polarization dependence of conical refraction.

Science.gov (United States)

Turpin, A; Loiko, Yu V; Kalkandjiev, T K; Tomizawa, H; Mompart, J

2013-02-25

We experimentally address the wave-vector and polarization dependence of the internal conical refraction phenomenon by demonstrating that an input light beam of elliptical transverse profile refracts into two beams after passing along one of the optic axes of a biaxial crystal, i.e. it exhibits double refraction instead of refracting conically. Such double refraction is investigated by the independent rotation of a linear polarizer and a cylindrical lens. Expressions to describe the position and the intensity pattern of the refracted beams are presented and applied to predict the intensity pattern for an axicon beam propagating along the optic axis of a biaxial crystal.

Past and present of corneal refractive surgery

DEFF Research Database (Denmark)

Vestergaard, Anders Højslet

Surgical correction of refractive errors is becoming increasingly popular. In the 1990s, the excimer laser revolutionized the field of corneal refractive surgery with PRK and LASIK, and lately refractive lenticule extraction (ReLEx) of intracorneal tissue, using only a femtosecond laser, has become...

Visual disability, visual function, and myopia among rural chinese secondary school children: the Xichang Pediatric Refractive Error Study (X-PRES)--report 1.

Science.gov (United States)

Congdon, Nathan; Wang, Yunfei; Song, Yue; Choi, Kai; Zhang, Mingzhi; Zhou, Zhongxia; Xie, Zhenling; Li, Liping; Liu, Xueyu; Sharma, Abhishek; Wu, Bin; Lam, Dennis S C

2008-07-01

To evaluate visual acuity, visual function, and prevalence of refractive error among Chinese secondary-school children in a cross-sectional school-based study. Uncorrected, presenting, and best corrected visual acuity, cycloplegic autorefraction with refinement, and self-reported visual function were assessed in a random, cluster sample of rural secondary school students in Xichang, China. Among the 1892 subjects (97.3% of the consenting children, 84.7% of the total sample), mean age was 14.7 +/- 0.8 years, 51.2% were female, and 26.4% were wearing glasses. The proportion of children with uncorrected, presenting, and corrected visual disability (visual disability when tested without correction, 98.7% was due to refractive error, while only 53.8% (414/770) of these children had appropriate correction. The girls had significantly (P visual disability and myopia visual function (ANOVA trend test, P Visual disability in this population was common, highly correctable, and frequently uncorrected. The impact of refractive error on self-reported visual function was significant. Strategies and studies to understand and remove barriers to spectacle wear are needed.

Human resources for refraction services in Central Nepal.

Science.gov (United States)

Kandel, Himal; Murthy, G V S; Bascaran, Covadonga

2015-07-01

Uncorrected refractive error is a public health problem globally and in Nepal. Planning of refraction services is hampered by a paucity of data. This study was conducted to determine availability and distribution of human resources for refraction, their efficiency, the type and extent of their training; the current service provision of refraction services and the unmet need in human resources for refraction in Central Nepal. This was a descriptive cross-sectional study. All refraction facilities in the Central Region were identified through an Internet search and interviews of key informants from the professional bodies and parent organisations of primary eye centres. A stratified simple random sampling technique was used to select 50 per cent of refraction facilities. The selected facilities were visited for primary data collection. Face-to-face interviews were conducted with the managers and the refractionists available in the facilities using a semi-structured questionnaire. Data was collected in 29 centres. All the managers (n=29; response rate 100 per cent) and 50 refractionists (Response rate 65.8 per cent) were interviewed. Optometrists and ophthalmic assistants were the main providers of refraction services (n=70, 92.11 per cent). They were unevenly distributed across the region, highly concentrated around urban areas. The median number of refractions per refractionist per year was 3,600 (IQR: 2,400 - 6,000). Interviewed refractionists stated that clients' knowledge, attitude and practice related factors such as lack of awareness of the need for refraction services and/or availability of existing services were the major barriers to the output of refraction services. The total number of refractions carried out in the Central Region per year was 653,176. An additional 170 refractionists would be needed to meet the unmet need of 1,323,234 refractions. The study findings demand a major effort to develop appropriately trained personnel when planning

Fully 3D refraction correction dosimetry system

International Nuclear Information System (INIS)

Manjappa, Rakesh; Makki, S Sharath; Kanhirodan, Rajan; Kumar, Rajesh; Vasu, Ram Mohan

2016-01-01

The irradiation of selective regions in a polymer gel dosimeter results in an increase in optical density and refractive index (RI) at those regions. An optical tomography-based dosimeter depends on rayline path through the dosimeter to estimate and reconstruct the dose distribution. The refraction of light passing through a dose region results in artefacts in the reconstructed images. These refraction errors are dependant on the scanning geometry and collection optics. We developed a fully 3D image reconstruction algorithm, algebraic reconstruction technique-refraction correction (ART-rc) that corrects for the refractive index mismatches present in a gel dosimeter scanner not only at the boundary, but also for any rayline refraction due to multiple dose regions inside the dosimeter. In this study, simulation and experimental studies have been carried out to reconstruct a 3D dose volume using 2D CCD measurements taken for various views. The study also focuses on the effectiveness of using different refractive-index matching media surrounding the gel dosimeter. Since the optical density is assumed to be low for a dosimeter, the filtered backprojection is routinely used for reconstruction. We carry out the reconstructions using conventional algebraic reconstruction (ART) and refractive index corrected ART (ART-rc) algorithms. The reconstructions based on FDK algorithm for cone-beam tomography has also been carried out for comparison. Line scanners and point detectors, are used to obtain reconstructions plane by plane. The rays passing through dose region with a RI mismatch does not reach the detector in the same plane depending on the angle of incidence and RI. In the fully 3D scanning setup using 2D array detectors, light rays that undergo refraction are still collected and hence can still be accounted for in the reconstruction algorithm. It is found that, for the central region of the dosimeter, the usable radius using ART-rc algorithm with water as RI matched

Fully 3D refraction correction dosimetry system.

Science.gov (United States)

Manjappa, Rakesh; Makki, S Sharath; Kumar, Rajesh; Vasu, Ram Mohan; Kanhirodan, Rajan

2016-02-21

The irradiation of selective regions in a polymer gel dosimeter results in an increase in optical density and refractive index (RI) at those regions. An optical tomography-based dosimeter depends on rayline path through the dosimeter to estimate and reconstruct the dose distribution. The refraction of light passing through a dose region results in artefacts in the reconstructed images. These refraction errors are dependant on the scanning geometry and collection optics. We developed a fully 3D image reconstruction algorithm, algebraic reconstruction technique-refraction correction (ART-rc) that corrects for the refractive index mismatches present in a gel dosimeter scanner not only at the boundary, but also for any rayline refraction due to multiple dose regions inside the dosimeter. In this study, simulation and experimental studies have been carried out to reconstruct a 3D dose volume using 2D CCD measurements taken for various views. The study also focuses on the effectiveness of using different refractive-index matching media surrounding the gel dosimeter. Since the optical density is assumed to be low for a dosimeter, the filtered backprojection is routinely used for reconstruction. We carry out the reconstructions using conventional algebraic reconstruction (ART) and refractive index corrected ART (ART-rc) algorithms. The reconstructions based on FDK algorithm for cone-beam tomography has also been carried out for comparison. Line scanners and point detectors, are used to obtain reconstructions plane by plane. The rays passing through dose region with a RI mismatch does not reach the detector in the same plane depending on the angle of incidence and RI. In the fully 3D scanning setup using 2D array detectors, light rays that undergo refraction are still collected and hence can still be accounted for in the reconstruction algorithm. It is found that, for the central region of the dosimeter, the usable radius using ART-rc algorithm with water as RI matched

Can the Bruckner test be used as a rapid screening test to detect significant refractive errors in children?

Directory of Open Access Journals (Sweden)

Kothari Mihir

2007-01-01

Full Text Available Purpose: To assess the suitability of Brückner test as a screening test to detect significant refractive errors in children. Materials and Methods: A pediatric ophthalmologist prospectively observed the size and location of pupillary crescent on Brückner test as hyperopic, myopic or astigmatic. This was compared with the cycloplegic refraction. Detailed ophthalmic examination was done for all. Sensitivity, specificity, positive predictive value and negative predictive value of Brückner test were determined for the defined cutoff levels of ametropia. Results: Ninety-six subjects were examined. Mean age was 8.6 years (range 1 to 16 years. Brückner test could be completed for all; the time taken to complete this test was 10 seconds per subject. The ophthalmologist identified 131 eyes as ametropic, 61 as emmetropic. The Brückner test had sensitivity 91%, specificity 72.8%, positive predictive value 85.5% and negative predictive value 83.6%. Of 10 false negatives four had compound hypermetropic astigmatism and three had myopia. Conclusions: Brückner test can be used to rapidly screen the children for significant refractive errors. The potential benefits from such use may be maximized if programs use the test with lower crescent measurement cutoffs, a crescent measurement ruler and a distance fixation target.

Refractive and Biometric Outcomes in Patients with Retinopathy of Prematurity Treated with Intravitreal Injection of Ranibizumab as Compared with Bevacizumab: A Clinical Study of Correction at Three Years of Age.

Science.gov (United States)

Chen, Yen-Chih; Chen, San-Ni; Yang, Benjamin Chi-Lan; Lee, Kun-Hsien; Chuang, Chih-Chun; Cheng, Chieh-Yin

2018-01-01

To compare refractive and biometric outcomes in patients with type 1 retinopathy of prematurity (ROP) treated with intravitreal injection of ranibizumab (IVR) versus bevacizumab (IVB), at a corrected age of 3 years. A retrospective case series compared cycloplegic refractive statuses and biometric statuses in patients who received either IVR or IVB for type 1 ROP, from April 2011 to April 2014. A total of 62 eyes (33 patients) with type 1 ROP were evaluated (26 eyes in 13 IVR patients and 36 eyes in 20 IVB patients). There were no differences in birth statuses including gestational age and birth body weight between the two groups. The prevalence of refractive error greater than 1 D was higher in the IVB group ( p = 0.03), and there was a higher prevalence of high myopia (biometric finding showed that IVB patients had shallower anterior chamber depth ( p = 0.01). Both IVR and IVB showed low refractive errors, even followed at the corrected age of 3 years. No difference was noted between the two groups in refractive statuses. However, IVB was associated with shallower anterior chamber and higher prevalence of refractive error at the corrected age of 3 years. This trial is registered with NCT03334513.

Dark refraction shift with allowance for astigmatism

Directory of Open Access Journals (Sweden)

W.D.H. Gillan

2005-12-01

Full Text Available Purpose: To show that the dark refraction shift (dark focus is a more complicated phenomenon than implied when presented as spherical. Methods: Fifty autorefractor measurements of refractive state of the right eye were obtained in light  and  dark  conditions.  Multivariate  methods were used to analyze the data and stereo-pair scat-ter plots, polar meridional profiles and other means of presenting results are used to show important characteristics of the dark refraction shift. Results: The complexity of the dark refrac-tion shift is indicated by stereo-pair scatter plots showing the amount of stigmatic and antistigmatic variation that occurs in light and dark conditions. The mean dark refraction shift is presented in a complete manner including all three components of refractive state. The greater variance and covari-ance under dark conditions is clearly shown by the term-by-term dark-light variance-covariance ratio and polar profiles  of variance and covariance.Conclusions: The  dark  refraction  shift  is  a more complicated phenomenon than implied by representations as purely spherical in nature.

Super-Virtual Refraction Interferometric Redatuming: Enhancing the Refracted Energy

KAUST Repository

Aldawood, Ali

2012-02-26

onshore seismic data processing. Refraction tomography is becoming a common way to estimate an accurate near surface velocity model. One of the problems with refraction tomography is the low signal to noise ration in far offset data. To improve, we propose using super-virtual refraction interferometry to enhance the weak energy at far offsets. We use Interferometric Green\\'s functions to redatum sources by cross-correlating two traces recorded at receiver stations, A and B, from a source at location W. The result is a redatumed trace with a virtual source at A and a receiver at B, which can also be obtained by correlating two traces recorded at A and B from different shots. Stacking them would enhance the signal-to-noise ratio of this "virtual" trace. We next augment redatuming with convolution and stacking. The trace recorded at B from a virtual source at A is convolved with the original trace recorded at A from a source at W. The result is a "super-virtual" trace at B in the far-offset from a source at W. Stacking N traces gives a vN-improvement. We applied our method to noisy synthetic and field data recorded over a complex near-surface and we could pick more traces at far offsets. It was possible to accommodate more picks resulting in a better subsurface coverage

Super-Virtual Refraction Interferometric Redatuming: Enhancing the Refracted Energy

KAUST Repository

Aldawood, Ali; Alshuhail, Abdulrahman Abdullatif Abdulrahman; Hanafy, Sherif

2012-01-01

onshore seismic data processing. Refraction tomography is becoming a common way to estimate an accurate near surface velocity model. One of the problems with refraction tomography is the low signal to noise ration in far offset data. To improve, we propose using super-virtual refraction interferometry to enhance the weak energy at far offsets. We use Interferometric Green's functions to redatum sources by cross-correlating two traces recorded at receiver stations, A and B, from a source at location W. The result is a redatumed trace with a virtual source at A and a receiver at B, which can also be obtained by correlating two traces recorded at A and B from different shots. Stacking them would enhance the signal-to-noise ratio of this "virtual" trace. We next augment redatuming with convolution and stacking. The trace recorded at B from a virtual source at A is convolved with the original trace recorded at A from a source at W. The result is a "super-virtual" trace at B in the far-offset from a source at W. Stacking N traces gives a vN-improvement. We applied our method to noisy synthetic and field data recorded over a complex near-surface and we could pick more traces at far offsets. It was possible to accommodate more picks resulting in a better subsurface coverage

Refractive regression after laser in situ keratomileusis.

Science.gov (United States)

Yan, Mabel K; Chang, John Sm; Chan, Tommy Cy

2018-04-26

Uncorrected refractive errors are a leading cause of visual impairment across the world. In today's society, laser in situ keratomileusis (LASIK) has become the most commonly performed surgical procedure to correct refractive errors. However, regression of the initially achieved refractive correction has been a widely observed phenomenon following LASIK since its inception more than two decades ago. Despite technological advances in laser refractive surgery and various proposed management strategies, post-LASIK regression is still frequently observed and has significant implications for the long-term visual performance and quality of life of patients. This review explores the mechanism of refractive regression after both myopic and hyperopic LASIK, predisposing risk factors and its clinical course. In addition, current preventative strategies and therapies are also reviewed. © 2018 Royal Australian and New Zealand College of Ophthalmologists.

Refracting surface plasmon polaritons with nanoparticle arrays

DEFF Research Database (Denmark)

Radko, I.P.; Evlyukhin, A.B.; Boltasseva, Alexandra

2008-01-01

Refraction of surface plasmon polaritons (SPPs) by various structures formed by a 100-nm-period square lattice of gold nanoparticles on top of a gold film is studied by leakage radiation microscopy. SPP refraction by a triangular-shaped nanoparticle array indicates that the SPP effective refractive...... to design nanoparticle arrays for specific applications requiring in-plane SPP manipulation....

Measurement of the effective refractive index of a turbid colloidal suspension using light refraction

International Nuclear Information System (INIS)

Reyes-Coronado, A; Garcia-Valenzuela, A; Sanchez-Perez, C; Barrera, R G

2005-01-01

We propose and analyse a simple method to measure simultaneously the real and imaginary parts of the effective refractive index of a turbid suspension of particles. The method is based on measurements of the angle of refraction and transmittance of a laser beam that traverses a hollow glass prism filled with a colloidal suspension. We provide a comprehensive assessment of the method. It can offer high sensitivity while still being simple to interpret. We present results of experiments using an optically turbid suspension of polystyrene particles and compare them with theoretical predictions. We also report experimental evidence showing that the refractive behaviour of the diffuse component of light coming from a suspension depends on the volume fraction of the colloidal particles

Compound refractive X-ray lens

International Nuclear Information System (INIS)

Nygren, D.R.; Cahn, R.; Cederstrom, B.; Danielsson, M.; Vestlund, J.

2000-01-01

An apparatus and method are disclosed for focusing X-rays. In one embodiment, his invention is a commercial-grade compound refractive X-ray lens. The commercial-grade compound refractive X-ray lens includes a volume of low-Z material. The volume of low-Z material has a first surface which is adapted to receive X-rays of commercially-applicable power emitted from a commercial-grade X-ray source. The volume of low-Z material also has a second surface from which emerge the X-rays of commercially-applicable power which were received at the first surface. Additionally, the commercial-grade compound refractive X-ray lens includes a plurality of openings which are disposed between the first surface and the second surface. The plurality of openings are oriented such that the X-rays of commercially-applicable power which are received at the first surface, pass through the volume of low-Z material and through the plurality openings. In so doing, the X-rays which emerge from the second surface are refracted to a focal point

Compound refractive X-ray lens

Science.gov (United States)

Nygren, David R.; Cahn, Robert; Cederstrom, Bjorn; Danielsson, Mats; Vestlund, Jonas

2000-01-01

An apparatus and method for focusing X-rays. In one embodiment, his invention is a commercial-grade compound refractive X-ray lens. The commercial-grade compound refractive X-ray lens includes a volume of low-Z material. The volume of low-Z material has a first surface which is adapted to receive X-rays of commercially-applicable power emitted from a commercial-grade X-ray source. The volume of low-Z material also has a second surface from which emerge the X-rays of commercially-applicable power which were received at the first surface. Additionally, the commercial-grade compound refractive X-ray lens includes a plurality of openings which are disposed between the first surface and the second surface. The plurality of openings are oriented such that the X-rays of commercially-applicable power which are received at the first surface, pass through the volume of low-Z material and through the plurality openings. In so doing, the X-rays which emerge from the second surface are refracted to a focal point.

The generalized vectorial laws of reflection and refraction

International Nuclear Information System (INIS)

Bhattacharjee, Pramode Ranjan

2005-01-01

This paper discloses two important discoveries. These are: (i) discovery of ambiguity in the well-established laws of reflection and refraction of light which have been in regular use for many years, and (ii) discovery of generalized vectorial laws of reflection and refraction of light. The existing definitions of angle of incidence, angle of reflection and angle of refraction are considered first. Each of these definitions is found to be ambiguous, not in compliance with the fundamental definition of angle in geometry. Two typical questions (one in the case of reflection and the other for refraction) have been addressed, which cannot be dealt with by using the existing laws of reflection and refraction of light. Thus, the existing laws of reflection and refraction of light seem to be ambiguous in respect of generality and their validity in a broad sense is questionable. With a view to removing the ambiguities, proper definitions of the above three angles are given first and then the statement of the generalized vectorial law of reflection (as well as that of refraction) has been offered

Physics of negative refractive index materials

International Nuclear Information System (INIS)

Ramakrishna, S Anantha

2005-01-01

In the past few years, new developments in structured electromagnetic materials have given rise to negative refractive index materials which have both negative dielectric permittivity and negative magnetic permeability in some frequency ranges. The idea of a negative refractive index opens up new conceptual frontiers in photonics. One much-debated example is the concept of a perfect lens that enables imaging with sub-wavelength image resolution. Here we review the fundamental concepts and ideas of negative refractive index materials. First we present the ideas of structured materials or meta-materials that enable the design of new materials with a negative dielectric permittivity, negative magnetic permeability and negative refractive index. We discuss how a variety of resonance phenomena can be utilized to obtain these materials in various frequency ranges over the electromagnetic spectrum. The choice of the wave-vector in negative refractive index materials and the issues of dispersion, causality and energy transport are analysed. Various issues of wave propagation including nonlinear effects and surface modes in negative refractive materials (NRMs) are discussed. In the latter part of the review, we discuss the concept of a perfect lens consisting of a slab of a NRM. This perfect lens can image the far-field radiative components as well as the near-field evanescent components, and is not subject to the traditional diffraction limit. Different aspects of this lens such as the surface modes acting as the mechanism for the imaging of the evanescent waves, the limitations imposed by dissipation and dispersion in the negative refractive media, the generalization of this lens to optically complementary media and the possibility of magnification of the near-field images are discussed. Recent experimental developments verifying these ideas are briefly covered

Refractive Lens Exchange with Multifocal Intraocular Lens for Treatment of Chronic Intermittent Spasm of the Near Reflex

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Guy Sallet

2017-12-01

Full Text Available We report the case of an emmetropic 32-year-old female with decreased uncorrected visual acuity and diplopia due to intermittent episodes of spasm of the near reflex. Neurologic, general, and ophthalmic examination could not find an organic cause. Attempts at spontaneous recovery, psychogenic therapy, and cycloplegic therapy were unsuccessful and the symptoms persisted for almost 5 years, leading to psychogenic distress. Final treatment with refractive lens exchange and implantation of a toric trifocal intraocular lens resolved the spasm of the near reflex, resulting in an uncorrected distance and near visual acuity of 20/20.

Refractive accuracy with light-adjustable intraocular lenses.

Science.gov (United States)

Villegas, Eloy A; Alcon, Encarna; Rubio, Elena; Marín, José M; Artal, Pablo

2014-07-01

To evaluate efficacy, predictability, and stability of refractive treatments using light-adjustable intraocular lenses (IOLs). University Hospital Virgen de la Arrixaca, Murcia, Spain. Prospective nonrandomized clinical trial. Eyes with a light-adjustable IOL (LAL) were treated with spatial intensity profiles to correct refractive errors. The effective changes in refraction in the light-adjustable IOL after every treatment were estimated by subtracting those in the whole eye and the cornea, which were measured with a Hartmann-Shack sensor and a corneal topographer, respectively. The refractive changes in the whole eye and light-adjustable IOL, manifest refraction, and visual acuity were obtained after every light treatment and at the 3-, 6-, and 12-month follow-ups. The study enrolled 53 eyes (49 patients). Each tested light spatial pattern (5 spherical; 3 astigmatic) produced a different refractive change (Plight adjustments induced a maximum change in spherical power of the light-adjustable IOL of between -1.98 diopters (D) and +2.30 D and in astigmatism of up to -2.68 D with axis errors below 9 degrees. Intersubject variability (standard deviation) ranged between 0.10 D and 0.40 D. The 2 required lock-in procedures induced a small myopic shift (range +0.01 to +0.57 D) that depended on previous adjustments. Light-adjustable IOL implantation achieved accurate refractive outcomes (around emmetropia) with good uncorrected distance visual acuity, which remained stable over time. Further refinements in nomograms and in the treatment's protocol would improve the predictability of refractive and visual outcomes with these IOLs. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Refractive index contrast in porous silicon multilayers

Energy Technology Data Exchange (ETDEWEB)

Nava, R.; Mora, M.B. de la; Tagueena-Martinez, J. [Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Temixco, Morelos (Mexico); Rio, J.A. del [Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Temixco, Morelos (Mexico); Centro Morelense de Innovacion y Transferencia Tecnologica, Consejo de Ciencia y Tecnologia del Estado de Morelos (Mexico)

2009-07-15

Two of the most important properties of a porous silicon multilayer for photonic applications are flat interfaces and a relative large refractive index contrast between layers in the optical wavelength range. In this work, we studied the effect of the current density and HF electrolyte concentration on the refractive index of porous silicon. With the purpose of increasing the refractive index contrast in a multilayer, the refractive index of porous silicon produced at low current was studied in detail. The current density applied to produce the low porosity layers was limited in order to keep the electrolyte flow through the multilayer structure and to avoid deformation of layer interfaces. We found that an electrolyte composed of hydrofluoric acid, ethanol and glycerin in a ratio of 3:7:1 gives a refractive index contrast around 1.3/2.8 at 600 nm. Several multilayer structures with this refractive index contrast were fabricated, such as dielectric Bragg mirrors and microcavities. Reflectance spectra of the structures show the photonic quality of porous silicon multilayers produced under these electrochemical conditions. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Development of a subjective refraction simulator

Science.gov (United States)

Perches, S.; Ares, J.; Collados, M. V.

2013-11-01

We have developed simulation software by Matlab (MathworksInc.) with a graphical interface designed for non-expert users. This simulator allows you to complete the process of subjective refraction starting from the aberrometry of the patients and analyse the influence of different factors during the exam. In addition to explain the graphical interface and its working, we show two examples about a complete process of subjective refraction with the influence of high order aberrations and without them showing the retinal image obtained in each step of the refraction process. When the Jackson Cross-Cylinder technique is made with this software, it becomes clear the difficulty of chosen between two images when high order aberrations are present. Therefore, the variability of response during the refraction can be a problem when the examiner has to reach an adequate optical prescription.

Isaac Newton and the astronomical refraction.

Science.gov (United States)

Lehn, Waldemar H

2008-12-01

In a short interval toward the end of 1694, Isaac Newton developed two mathematical models for the theory of the astronomical refraction and calculated two refraction tables, but did not publish his theory. Much effort has been expended, starting with Biot in 1836, in the attempt to identify the methods and equations that Newton used. In contrast to previous work, a closed form solution is identified for the refraction integral that reproduces the table for his first model (in which density decays linearly with elevation). The parameters of his second model, which includes the exponential variation of pressure in an isothermal atmosphere, have also been identified by reproducing his results. The implication is clear that in each case Newton had derived exactly the correct equations for the astronomical refraction; furthermore, he was the first to do so.

Refractive outcome of premature infants with or without retinopathy of prematurity at 2 years of age: A prospective controlled cohort study

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Ching-ju Hsieh

2012-04-01

Full Text Available This study evaluated the extent to which refractive morbidity is correlated to preterm birth or retinopathy of prematurity (ROP itself, or both, and examined the risk factors associated with refractive errors in a cohort of preterm infants with and without ROP compared with full-term infants. This longitudinal, prospective, controlled cohort study enrolled 109 infants, including 74 preterm and 35 full-term infants. Infants were divided into the following groups: no ROP, regressed ROP, laser-treated threshold ROP, and full-term. Cycloplegic refraction was determined at 6 and 24 months’ corrected age. Multiple regression models, analysis of variance (ANOVA with post hoc comparisons, paired t test, and the χ2 test were used for data analysis. ROP status was highly predictive of significant refractive errors in preterm infants. Eyes with laser-treated threshold ROP had significant myopia at both ages (mean spherical equivalent [MSE] in right eye at both refractions −0.72, −1.21 diopters [D], astigmatism (MSE −1.62, −1.80 D, and anisometropia (MSE 0.82, 1.02 D; ANOVA p  0.05. Thus, the persistent hyperopic status across ages in patients with regressed ROP and in patients without ROP differed significantly (paired t test p > 0.05 from that in the full-term infants, with a reduction in hypermetropia noted for the first 2 years of life (paired t test p < 0.05. The incidence and magnitude of significant refractive errors increased with severe ROP and with age. Although the emmetropization process of preterm birth, including regressed ROP and no ROP, differed from full-term birth in early infancy, we found no differences in the refractive status after 1 year in patients with regressed ROP and in patients without ROP, who were at risk of developing ametropia similar to that of full-term patients. Therefore, apart from laser-treated ROP, children with regressed ROP and without ROP can likely be observed with a verbal vision screening at 3�

Refração e seus componentes em anisometropia Refraction and its components in anisometropia

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David Tayah

2009-02-01

Full Text Available OBJETIVO: Em anisométropes comparar os valores médios individuais dos componentes oculares de ambos os olhos, correlacionar as diferenças dos componentes com as diferenças de refração; e identificar o menor número de fatores que contenham o mesmo grau de informações expressas no conjunto de variáveis que influenciam a diferença refrativa. MÉTODOS: Realizou-se estudo transversal analítico em população de 77 anisométropes de 2 D ou mais, atendida no ambulatório de Oftalmologia do Hospital Universitário da Faculdade de Medicina Nilton Lins, Manaus. RESULTADOS: Os anisométropes foram submetidos à refração estática objetiva e subjetiva, ceratometria e biometria ultrassônica A-scan. A análise dos dados foi feita por meio dos seguintes modelos estatísticos: análise univariada, multivariada, de regressão múltipla e fatorial. CONCLUSÕES: Não houve diferenças significativas na comparação dos valores médios individuais dos componentes oculares entre os olhos. Houve correlação negativa média entre a diferença refrativa e a diferença de comprimento axial (r= -0,64 (pPURPOSE: To compare the individual means of ocular components of both eyes in patients with anisometropia; to correlate the differences of the components with refractive differences; and to identify the smallest number of factors that contain the same level of information expressed in the set of variables that influence refractive difference. METHODS: An analytical transversal study was carried out in 77 patients with anisometropia of two or more dioptres seen at the Ophthalmologic Clinic, University Hospital, Nilton Lins Medical School, Manaus. RESULTS: All participants were submitted to ophthalmologic examination which included objective and subjective cycloplegic refractometry, keratometry and ultrasound biometry. Data analysis comprised the following statistical models: univariate, multivariate, multiple and factorial regression analyses. CONCLUSIONS

3D super-virtual refraction interferometry

KAUST Repository

Lu, Kai; AlTheyab, Abdullah; Schuster, Gerard T.

2014-01-01

Super-virtual refraction interferometry enhances the signal-to-noise ratio of far-offset refractions. However, when applied to 3D cases, traditional 2D SVI suffers because the stationary positions of the source-receiver pairs might be any place

Pediatric PRK (PhotoRefractive Keratectomy) with Mitomycin C (MCC) for Persistent Anisometropic Amblyopia. A Case Report.

Science.gov (United States)

Crawford, Courtney M; Frazier, Travis C; Torres, Mark F; Arnold, Robert W; Mazzoli, Robert A; Raymond, William R

2012-01-01

To evaluate the safety and efficacy of photorefractive keratectomy (PRK) with Mitomycin C (MMC) for the treatment of severe pediatric anisometropia and amblyopia resistant to more conservative treatment modalities. A 3 year-old-child, who at 18 months old underwent unilateral diode laser treatment for threshold ROP, developed 11 diopters of anisometropic myopia and secondary dense amblyopia of the Right Eye. Only after all conservative treatment options failed was he treated with PRK and MMC. Principal outcome measures included cycloplegic refraction, the amount of refractive correction, degree of corneal haze and change in visual acuity. On presentation: BCVA: 20/CF OD; 20/30 OS. CRNS: -11.50 diopters sphere OD; -0.50 diopters sphere OS. Unilateral PRK followed by application of MMC (0.2 mg/ml) for 1 min was performed under general anesthesia. Three-month postoperative findings include: VA: 20/30 OD; 20/25 OS. CRNS: +0.25 diopters sphere OD. At one year, the BCVA remained equal at the 20/30 level despite mild myopic regression OD. CRNS OD at one year was -1.25 +050 x 116. No corneal haze was appreciated. In this child, treatment with PRK and MMC safely reduced the anisometropia thus facilitating his visual rehabilitation. While encouraging, further study is required to verify the longer term results of this single case. To evaluate the safety and efficacy of photorefractive keratectomy (PRK) with Mitomycin C (MMC) for the treatment of severe pediatric anisometropia and amblyopia resistant to more conservative treatment modalities. A 3 year-old-child, who at 18 months old underwent unilateral diode laser treatment for threshold ROP, developed 11 diopters of anisometropic myopia and secondary dense amblyopia of the Right Eye. Only after all conservative treatment options failed was he treated with PRK and MMC. Principal outcome measures included cycloplegic refraction, the amount of refractive correction, degree of corneal haze and change in visual acuity. On

Exceptionally low prevalence of refractive error and visual impairment in schoolchildren from Lao People's Democratic Republic.

Science.gov (United States)

Casson, Robert J; Kahawita, Shyalle; Kong, Aimee; Muecke, James; Sisaleumsak, Siphetthavong; Visonnavong, Vithoune

2012-10-01

Vientiane Province is an urbanizing region in Southeast Asia. We aimed to determine the prevalence of refractive error and visual impairment in primary school-aged children in this region. Prospective, cross-sectional survey. A total of 2899 schoolchildren from Vientiane Province, Lao People's Democratic Republic (Lao PDR). Ten districts from Vientiane were randomly selected and 2 primary schools were randomly selected from each district. All children aged 6 to 11 years at selected schools were eligible to participate. The examination included visual acuity (VA) testing, cycloplegic retinoscopy with subjective refinement if indicated, ocular motility testing, and anterior segment and fundus examinations in visually impaired children. Cycloplegic refraction and VA. There was an estimated total of 3330 children who were eligible to participate, and data were recorded from 2899 (87%) of these children. Complete refractive data were available on 2842 children (85% of eligible population). The mean spherical equivalent (SE) in the right eyes was +0.60 diopter (D) (95% confidence interval [CI], 0.49-0.72), and the mean SE in the left eyes was +0.59 (95% CI, 0.50-0.68). The prevalence of hyperopia was 2.8% (95% CI, 1.9-3.7; 88 subjects), and the prevalence of myopia was 0.8% (95% CI, 0.3-1.4; 24 subjects). The majority of children (98%; 95% CI, 97.0-99.0) had normal unaided binocular VA (at least 20/32 in their better eye). The overall prevalence of any visual impairment (presenting VA <20/32 in the better eye) was 1.9% (95% CI, 1.0-2.9; 55 subjects). In multivariate logistic regression analysis, age (P = 0.001) was a significant predictor, and female gender (P = 0.08) and Yao ethnicity (P = 0.09) were borderline significant predictors of the presence of any visual impairment. Visual impairment is not a public health concern in this primary school-aged population; however, visually impaired children in the community were not studied. From this baseline, future surveys

Differences between wavefront and subjective refraction for infrared light.

Science.gov (United States)

Teel, Danielle F W; Jacobs, Robert J; Copland, James; Neal, Daniel R; Thibos, Larry N

2014-10-01

To determine the accuracy of objective wavefront refractions for predicting subjective refractions for monochromatic infrared light. Objective refractions were obtained with a commercial wavefront aberrometer (COAS, Wavefront Sciences). Subjective refractions were obtained for 30 subjects with a speckle optometer validated against objective Zernike wavefront refractions on a physical model eye (Teel et al., Design and validation of an infrared Badal optometer for laser speckle, Optom Vis Sci 2008;85:834-42). Both instruments used near-infrared (NIR) radiation (835 nm for COAS, 820 nm for the speckle optometer) to avoid correction for ocular chromatic aberration. A 3-mm artificial pupil was used to reduce complications attributed to higher-order ocular aberrations. For comparison with paraxial (Seidel) and minimum root-mean-square (Zernike) wavefront refractions, objective refractions were also determined for a battery of 29 image quality metrics by computing the correcting lens that optimizes retinal image quality. Objective Zernike refractions were more myopic than subjective refractions for 29 of 30 subjects. The population mean discrepancy was -0.26 diopters (D) (SEM = 0.03 D). Paraxial (Seidel) objective refractions tended to be hyperopically biased (mean discrepancy = +0.20 D, SEM = 0.06 D). Refractions based on retinal image quality were myopically biased for 28 of 29 metrics. The mean bias across all 31 measures was -0.24 D (SEM = 0.03). Myopic bias of objective refractions was greater for eyes with brown irises compared with eyes with blue irises. Our experimental results are consistent with the hypothesis that reflected NIR light captured by the aberrometer originates from scattering sources located posterior to the entrance apertures of cone photoreceptors, near the retinal pigment epithelium. The larger myopic bias for brown eyes suggests that a greater fraction of NIR light is reflected from choroidal melanin in brown eyes compared with blue eyes.

The refractive index of relic gravitons

CERN Document Server

Giovannini, Massimo

2016-01-01

The dynamical evolution of the refractive index of the tensor modes of the geometry produces a specific class of power spectra characterized by a blue (i.e. slightly increasing) slope which is directly determined by the competition of the slow-roll parameter and of the rate of variation of the refractive index. Throughout the conventional stages of the inflationary and post-inflationary evolution, the microwave background anisotropies measurements, the pulsar timing limits and the big-bang nucleosythesis constraints set stringent bounds on the refractive index and on its rate of variation. Within the physically allowed region of the parameter space the cosmic background of relic gravitons leads to a potentially large signal for the ground based detectors (in their advanced version) and for the proposed space-borne interferometers. Conversely, the lack of direct detection of the signal will set a qualitatively new bound on the dynamical variation of the refractive index.

Intelligent Planning for Laser Refractive Surgeries

Science.gov (United States)

Wang, Wei; Yue, Yong; Elsheikh, Ahmed; Bao, Fangjun

2018-02-01

Refractive error is one of leading ophthalmic diseases for both genders all over the world. Laser refractive correction surgery, e.g., laser in-situ keratomileusis (LASIK), has been commonly used worldwide. The prediction of surgical parameters, e.g., corneal ablation depth, depends on the doctor’s experience, theoretical formula and surgery reference manual in the preoperative diagnosis. The error of prediction may present a potential surgical risk and complication. Being aware of the surgery parameters is important because these can be used to estimate a patient’s post-operative visual quality and help the surgeon plan a suitable treatment. Therefore, in this paper we discuss data mining techniques that can be utilized for the prediction of laser refractive correction surgery parameters. It can provide the surgeon with a reference for possible surgical parameters and outcomes of the patient before the laser refractive correction surgery.

Peripheral refractive correction and automated perimetric profiles.

Science.gov (United States)

Wild, J M; Wood, J M; Crews, S J

1988-06-01

The effect of peripheral refractive error correction on the automated perimetric sensitivity profile was investigated on a sample of 10 clinically normal, experienced observers. Peripheral refractive error was determined at eccentricities of 0 degree, 20 degrees and 40 degrees along the temporal meridian of the right eye using the Canon Autoref R-1, an infra-red automated refractor, under the parametric conditions of the Octopus automated perimeter. Perimetric sensitivity was then undertaken at these eccentricities (stimulus sizes 0 and III) with and without the appropriate peripheral refractive correction using the Octopus 201 automated perimeter. Within the measurement limits of the experimental procedures employed, perimetric sensitivity was not influenced by peripheral refractive correction.

Reflective and refractive objects for mixed reality.

Science.gov (United States)

Knecht, Martin; Traxler, Christoph; Winklhofer, Christoph; Wimmer, Michael

2013-04-01

In this paper, we present a novel rendering method which integrates reflective or refractive objects into a differential instant radiosity (DIR) framework usable for mixed-reality (MR) applications. This kind of objects are very special from the light interaction point of view, as they reflect and refract incident rays. Therefore they may cause high-frequency lighting effects known as caustics. Using instant-radiosity (IR) methods to approximate these high-frequency lighting effects would require a large amount of virtual point lights (VPLs) and is therefore not desirable due to real-time constraints. Instead, our approach combines differential instant radiosity with three other methods. One method handles more accurate reflections compared to simple cubemaps by using impostors. Another method is able to calculate two refractions in real-time, and the third method uses small quads to create caustic effects. Our proposed method replaces parts in light paths that belong to reflective or refractive objects using these three methods and thus tightly integrates into DIR. In contrast to previous methods which introduce reflective or refractive objects into MR scenarios, our method produces caustics that also emit additional indirect light. The method runs at real-time frame rates, and the results show that reflective and refractive objects with caustics improve the overall impression for MR scenarios.

Refractive error magnitude and variability: Relation to age.

Science.gov (United States)

Irving, Elizabeth L; Machan, Carolyn M; Lam, Sharon; Hrynchak, Patricia K; Lillakas, Linda

2018-03-19

To investigate mean ocular refraction (MOR) and astigmatism, over the human age range and compare severity of refractive error to earlier studies from clinical populations having large age ranges. For this descriptive study patient age, refractive error and history of surgery affecting refraction were abstracted from the Waterloo Eye Study database (WatES). Average MOR, standard deviation of MOR and astigmatism were assessed in relation to age. Refractive distributions for developmental age groups were determined. MOR standard deviation relative to average MOR was evaluated. Data from earlier clinically based studies with similar age ranges were compared to WatES. Right eye refractive errors were available for 5933 patients with no history of surgery affecting refraction. Average MOR varied with age. Children <1 yr of age were the most hyperopic (+1.79D) and the highest magnitude of myopia was found at 27yrs (-2.86D). MOR distributions were leptokurtic, and negatively skewed. The mode varied with age group. MOR variability increased with increasing myopia. Average astigmatism increased gradually to age 60 after which it increased at a faster rate. By 85+ years it was 1.25D. J 0 power vector became increasingly negative with age. J 45 power vector values remained close to zero but variability increased at approximately 70 years. In relation to comparable earlier studies, WatES data were most myopic. Mean ocular refraction and refractive error distribution vary with age. The highest magnitude of myopia is found in young adults. Similar to prevalence, the severity of myopia also appears to have increased since 1931. Copyright © 2018 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.

Distribution of Binocular Vision Anomalies and Refractive Errors in Iranian Children With Learning Disabilities

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Yekta

2015-11-01

Full Text Available Background Visual problems in children contribute to learning disorders, which are one of the most influential factors in learning. Objectives The aim of the present study was to determine the prevalence of refractive and binocular vision errors in children with learning disorders. Patients and Methods In this cross-sectional study, 406 children with learning disorders with a mean age of 8.56 ± 2.4 years were evaluated. Examinations included the determination of refractive errors with an auto-refractometer and static retinoscopy, measurement of visual acuity with a Snellen chart, evaluation of ocular deviation, and measurement of stereopsis, amplitude of accommodation, and near point of convergence. Results Of the 406 participants, 319 (78.6% were emmetropic in the right eye, 14.5% had myopia, and 6.9% had hyperopia according to cycloplegic refraction. Astigmatism was detected in 75 (18.5% children. In our study, 89.9% of the children had no deviation, 1.0% had esophoria, and 6.4% had exophoria . In addition, 2.2% of the children had suppression. The near point of convergence ranged from 3 to 18 cm, with a mean of 10.12 ± 3.274 cm. Moreover, 98.5 and 98.0% of the participants achieved complete vision with the best correction in the right and left eye, respectively. The best corrected visual acuity in the right and left eye was achieved in 98.5 and 98.0% of the children, respectively. Conclusions The pattern of visual impairment in learning-impaired children is not much different from that in normal children; however, because these children may not be able to express themselves clearly, lack of correct diagnosis and appropriate treatment has resulted in a marked defect in recognizing visual disorders in these children. Therefore, gaining knowledge of the prevalence of refractive errors in children with learning disorders can be considered the first step in their treatment.

Parsimonious wave-equation travel-time inversion for refraction waves

KAUST Repository

Fu, Lei

2017-02-14

We present a parsimonious wave-equation travel-time inversion technique for refraction waves. A dense virtual refraction dataset can be generated from just two reciprocal shot gathers for the sources at the endpoints of the survey line, with N geophones evenly deployed along the line. These two reciprocal shots contain approximately 2N refraction travel times, which can be spawned into O(N2) refraction travel times by an interferometric transformation. Then, these virtual refraction travel times are used with a source wavelet to create N virtual refraction shot gathers, which are the input data for wave-equation travel-time inversion. Numerical results show that the parsimonious wave-equation travel-time tomogram has about the same accuracy as the tomogram computed by standard wave-equation travel-time inversion. The most significant benefit is that a reciprocal survey is far less time consuming than the standard refraction survey where a source is excited at each geophone location.

Microstructured optical fiber refractive index sensor

DEFF Research Database (Denmark)

Town, Graham E.; McCosker, Ravi; Yuan, Scott Wu

2010-01-01

We describe a dual-core microstructured optical fiber designed for refractive index sensing of fluids. We show that by using the exponential dependence of intercore coupling on analyte refractive index, both large range and high sensitivity can be achieved in the one device. We also show...

Refraction in the lower troposphere: Higher order image distortion effects due to refractive profile curvature

Science.gov (United States)

Short, Daniel J.

There are many applications that rely on the propagation of light through the atmosphere - all of which are subject to atmospheric conditions. While there are obvious processes such as scattering due to particulates like clouds and dust that affect the received intensity of the radiation, the clear atmosphere can also cause significant effects. Refraction is a clear air effect that can cause a variety of phenomena such as apparent relocation, stretching and compression of objects when viewed through the atmosphere. Recently, there has been significant interest in studying the refractive effects for low angle paths within the troposphere, and in particular, near-horizontal paths in the Earth's boundary layer, which is adjacent to the ground. Refractive effects in this case become problematic for many terrestrial optical applications. For example, the pointing of a free space optical communication or a remote sensing system can suffer wandering effects, high-resolution imagery can present distorted and/or dislocated targets, optical tracking of targets can be inaccurate, and optical geodetic surveying accuracy is also very sensitive to the effects of refraction. The work in this dissertation was inspired by data from a time-lapse camera system that collects images of distant targets over a near-horizontal path along the ground. This system was used previously to study apparent diurnal image displacement and this dissertation extends that work by exploring the higher order effects that result from curvature in the vertical refractive index profile of the atmosphere. There are surprisingly few experiments involving atmospheric refractive effects that carefully correlate field data to analytical expressions and other factors such as meteorological data. In working with the time-lapse data, which is comprised of sequences of hundreds or thousands of images collected over durations of weeks or months, it is important to develop straightforward analysis techniques that can

[Refractive errors among schoolchildren in the central region of Togo].

Science.gov (United States)

Nonon Saa, K B; Atobian, K; Banla, M; Rédah, T; Maneh, N; Walser, A

2013-11-01

Untreated refractive errors represent the main visual impairment in the world but also the easiest to avoid. The goal of this survey is to use clinical and epidemiological data to efficiently plan distribution of corrective glasses in a project supported by the Swiss Red Cross in the central region of Togo. To achieve this goal, 66 primary schools were identified randomly in the catchment area of the project. The teachers at these schools were previously trained to test visual acuity (VA). The schoolchildren referred by these teachers were examined by eye care professionals. The schoolchildren with ametropia (VA≤7/10 in at least one eye) underwent cycloplegic autorefraction. Of a total of 19,252 registered schoolchildren, 13,039 underwent VA testing by the teachers (participation rate=68%). Among them, 366 cases of ametropia were identified (prevalence about 3%). The average age of the schoolchildren examined was 10.7±2.3years, with a sex ratio of 1.06. Autorefraction, which was performed for 37% of the schoolchildren with ametropia allowed them to be classified into three groups: hyperopia (4%), myopia (5%) and astigmatism of all types (91%). Regardless of the type of ametropia, the degree of severity was mild in 88%. The results of this survey have highlighted the importance of the teachers' contribution to eye care education in the struggle against refractive errors within the school environment, as well as helping to efficiently plan actions against ametropia. Copyright © 2013 Elsevier Masson SAS. All rights reserved.

Age-Specific Prevalence of Visual Impairment and Refractive Error in Children Aged 3-10 Years in Shanghai, China.

Science.gov (United States)

Ma, Yingyan; Qu, Xiaomei; Zhu, Xiaofeng; Xu, Xun; Zhu, Jianfeng; Sankaridurg, Padmaja; Lin, Senlin; Lu, Lina; Zhao, Rong; Wang, Ling; Shi, Huijing; Tan, Hui; You, Xiaofang; Yuan, Hong; Sun, Sifei; Wang, Mingjin; He, Xiangui; Zou, Haidong; Congdon, Nathan

2016-11-01

We assessed changes in age-specific prevalence of refractive error at the time of starting school, by comparing preschool and school age cohorts in Shanghai, China. A cross-sectional study was done in Jiading District, Shanghai during November and December 2013. We randomly selected 7 kindergartens and 7 primary schools, with probability proportionate to size. Chinese children (n = 8398) aged 3 to 10 years were enumerated, and 8267 (98.4%) were included. Children underwent distance visual acuity assessment and refraction measurement by cycloplegic autorefraction and subjective refraction. The prevalence of uncorrected visual acuity (UCVA), presenting visual acuity, and best-corrected visual acuity in the better eye of ≤20/40 was 19.8%, 15.5%, and 1.7%, respectively. Among those with UCVA ≤ 20/40, 93.2% could achieve visual acuity of ≥20/32 with refraction. Only 28.7% (n = 465) of children with UCVA in the better eye of ≤20/40 wore glasses. Prevalence of myopia (spherical equivalent ≤-0.5 diopters [D] in at least one eye) increased from 1.78% in 3-year-olds to 52.2% in 10-year-olds, while prevalence of hyperopia (spherical equivalent ≥+2.0 D) decreased from 17.8% among 3-year-olds to 2.6% by 10 years of age. After adjusting for age, attending elite "high-level" school was statistically associated with greater myopia prevalence. The prevalence of myopia was lower or comparable to that reported in other populations from age 3 to 5 years, but increased dramatically after 6 years, consistent with a strong environmental role of schooling on myopia development.

The refractive index of human hemoglobin in the visible range

International Nuclear Information System (INIS)

Zhernovaya, O; Tuchin, V; Sydoruk, O; Douplik, A

2011-01-01

Because the refractive index of hemoglobin in the visible range is sensitive to the hemoglobin concentration, optical investigations of hemoglobin are important for medical diagnostics and treatment. Direct measurements of the refractive index are, however, challenging; few such measurements have previously been reported, especially in a wide wavelength range. We directly measured the refractive index of human deoxygenated and oxygenated hemoglobin for nine wavelengths between 400 and 700 nm for the hemoglobin concentrations up to 140 g l -1 . This paper analyzes the results and suggests a set of model functions to calculate the refractive index depending on the concentration. At all wavelengths, the measured values of the refractive index depended on the concentration linearly. Analyzing the slope of the lines, we determined the specific refraction increments, derived a set of model functions for the refractive index depending on the concentration, and compared our results with those available in the literature. Based on the model functions, we further calculated the refractive index at the physiological concentration within the erythrocytes of 320 g l -1 . The results can be used to calculate the refractive index in the visible range for arbitrary concentrations provided that the refractive indices depend on the concentration linearly.

Negative Refraction Angular Characterization in One-Dimensional Photonic Crystals

OpenAIRE

Lugo, Jesus Eduardo; Doti, Rafael; Faubert, Jocelyn

2011-01-01

Background Photonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity de...

Experimental Determination of Refractive Index of Gas Hydrates

DEFF Research Database (Denmark)

Bylov, Martin; Rasmussen, Peter

1997-01-01

. For methane hydrate (structure I) the refractive index was found to be 1.346 and for natural gas hydrate (structure II) it was found to be 1.350. The measurements further suggest that the gas hydrate growth rate increases if the water has formed hydrates before. The induction time, on the other hand, seems......The refractive indexes of methane hydrate and natural gas hydrate have been experimentally determined. The refractive indexes were determined in an indirect manner making use of the fact that two non-absorbing materials will have the same refractive index if they cannot be distinguished visually...

Characterizing conical refraction optical tweezers

Science.gov (United States)

McDonald, C.; McDougall, C.; Rafailov, E.; McGloin, D.

2014-12-01

Conical refraction occurs when a beam of light travels through an appropriately cut biaxial crystal. By focussing the conically refracted beam through a high numerical aperture microscope objective, conical refraction optical tweezers can be created, allowing for particle manipulation in both Raman spots and in the Lloyd/Poggendorff rings. We present a thorough quantification of the trapping properties of such a beam, focussing on the trap stiffness and how this varies with trap power and trapped particle location. We show that the lower Raman spot can be thought of as a single-beam optical gradient force trap, while radiation pressure dominates in the upper Raman spot, leading to optical levitation rather than trapping. Particles in the Lloyd/Poggendorff rings experience a lower trap stiffness than particles in the lower Raman spot but benefit from rotational control.

Macroeconomic landscape of refractive surgery in the United States.

Science.gov (United States)

Corcoran, Kevin J

2015-07-01

This review examines the economic history of refractive surgery and the decline of laser-assisted in-situ keratomileusis (LASIK) in the USA, and the emergence of refractive cataract surgery as an area of growth. Since it peaked in 2007 at 1.4 million procedures per year, LASIK has declined 50% in the USA, whereas refractive cataract surgery, including presbyopia-correcting intraocular lenses (IOLs), astigmatism-correcting IOLs, and femtosecond laser-assisted cataract surgery, has grown to 350 000 procedures per year, beginning in 2003. Patients are price-sensitive and responsive to publicity (good or bad) about refractive surgery and refractive cataract surgery. LASIK's decline has been partially offset by the emergence of refractive cataract surgery. About 11% of all cataract surgery in the USA involves presbyopia-correcting IOLs, astigmatism-correcting IOLs, or a femtosecond laser. From the surgeon's perspective, there are high barriers to entry into the marketplace for refractive surgery and refractive cataract surgery due to the high capital cost of excimer and femtosecond lasers, the high skill level required to deliver spectacular results to demanding patients who pay out of pocket, and the necessity to perform a high volume of surgeries to satisfy both of these requirements. Probably, less than 7% of US cataract surgeons can readily meet all of these requirements.

Refractive Errors Affect the Vividness of Visual Mental Images

Science.gov (United States)

Palermo, Liana; Nori, Raffaella; Piccardi, Laura; Zeri, Fabrizio; Babino, Antonio; Giusberti, Fiorella; Guariglia, Cecilia

2013-01-01

The hypothesis that visual perception and mental imagery are equivalent has never been explored in individuals with vision defects not preventing the visual perception of the world, such as refractive errors. Refractive error (i.e., myopia, hyperopia or astigmatism) is a condition where the refracting system of the eye fails to focus objects sharply on the retina. As a consequence refractive errors cause blurred vision. We subdivided 84 individuals according to their spherical equivalent refraction into Emmetropes (control individuals without refractive errors) and Ametropes (individuals with refractive errors). Participants performed a vividness task and completed a questionnaire that explored their cognitive style of thinking before their vision was checked by an ophthalmologist. Although results showed that Ametropes had less vivid mental images than Emmetropes this did not affect the development of their cognitive style of thinking; in fact, Ametropes were able to use both verbal and visual strategies to acquire and retrieve information. Present data are consistent with the hypothesis of equivalence between imagery and perception. PMID:23755186

Computational imaging using lightweight diffractive-refractive optics

KAUST Repository

Peng, Yifan

2015-11-23

Diffractive optical elements (DOE) show great promise for imaging optics that are thinner and more lightweight than conventional refractive lenses while preserving their light efficiency. Unfortunately, severe spectral dispersion currently limits the use of DOEs in consumer-level lens design. In this article, we jointly design lightweight diffractive-refractive optics and post-processing algorithms to enable imaging under white light illumination. Using the Fresnel lens as a general platform, we show three phase-plate designs, including a super-thin stacked plate design, a diffractive-refractive-hybrid lens, and a phase coded-aperture lens. Combined with cross-channel deconvolution algorithm, both spherical and chromatic aberrations are corrected. Experimental results indicate that using our computational imaging approach, diffractive-refractive optics is an alternative candidate to build light efficient and thin optics for white light imaging.

Computational imaging using lightweight diffractive-refractive optics

KAUST Repository

Peng, Yifan; Fu, Qiang; Amata, Hadi; Su, Shuochen; Heide, Felix; Heidrich, Wolfgang

2015-01-01

Diffractive optical elements (DOE) show great promise for imaging optics that are thinner and more lightweight than conventional refractive lenses while preserving their light efficiency. Unfortunately, severe spectral dispersion currently limits the use of DOEs in consumer-level lens design. In this article, we jointly design lightweight diffractive-refractive optics and post-processing algorithms to enable imaging under white light illumination. Using the Fresnel lens as a general platform, we show three phase-plate designs, including a super-thin stacked plate design, a diffractive-refractive-hybrid lens, and a phase coded-aperture lens. Combined with cross-channel deconvolution algorithm, both spherical and chromatic aberrations are corrected. Experimental results indicate that using our computational imaging approach, diffractive-refractive optics is an alternative candidate to build light efficient and thin optics for white light imaging.

Topography-modified refraction (TMR): adjustment of treated cylinder amount and axis to the topography versus standard clinical refraction in myopic topography-guided LASIK.

Science.gov (United States)

Kanellopoulos, Anastasios John

2016-01-01

To evaluate the safety, efficacy, and contralateral eye comparison of topography-guided myopic LASIK with two different refraction treatment strategies. Private clinical ophthalmology practice. A total of 100 eyes (50 patients) in consecutive cases of myopic topography-guided LASIK procedures with the same refractive platform (FS200 femtosecond and EX500 excimer lasers) were randomized for treatment as follows: one eye with the standard clinical refraction (group A) and the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction; group B). All cases were evaluated pre- and post-operatively for the following parameters: refractive error, best corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), topography (Placido-disk based) and tomography (Scheimpflug-image based), wavefront analysis, pupillometry, and contrast sensitivity. Follow-up visits were conducted for at least 12 months. Mean refractive error was -5.5 D of myopia and -1.75 D of astigmatism. In group A versus group B, respectively, the average UDVA improved from 20/200 to 20/20 versus 20/16; post-operative CDVA was 20/20 and 20/13.5; 1 line of vision gained was 27.8% and 55.6%; and 2 lines of vision gained was 5.6% and 11.1%. In group A, 27.8% of eyes had over -0.50 diopters of residual refractive astigmatism, in comparison to 11.7% in group B ( P Topography-modified refraction (TMR): topographic adjustment of the amount and axis of astigmatism treated, when different from the clinical refraction, may offer superior outcomes in topography-guided myopic LASIK. These findings may change the current clinical paradigm of the optimal subjective refraction utilized in laser vision correction.

Evidence for subwavelength imaging with positive refraction

Energy Technology Data Exchange (ETDEWEB)

Ma, Yun Gui [Temasek Laboratories, National University of Singapore, Singapore 119260 (Singapore); Sahebdivan, Sahar; Tyc, Tomas; Leonhardt, Ulf [School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom); Ong, C K, E-mail: ulf@st-andrews.ac.uk [Centre for Superconducting and Magnetic Materials, Department of Physics, National University of Singapore, Singapore 117542 (Singapore)

2011-03-15

The resolution of lenses is normally limited by the wave nature of light. Imaging with perfect resolution was believed to rely on negative refraction, but here we present experimental evidence for subwavelength imaging with positive refraction.

Evidence for subwavelength imaging with positive refraction

International Nuclear Information System (INIS)

Ma, Yun Gui; Sahebdivan, Sahar; Tyc, Tomas; Leonhardt, Ulf; Ong, C K

2011-01-01

The resolution of lenses is normally limited by the wave nature of light. Imaging with perfect resolution was believed to rely on negative refraction, but here we present experimental evidence for subwavelength imaging with positive refraction.

Prevalence of Visual Impairment and Refractive Errors in Children of South Sinai, Egypt.

Science.gov (United States)

Yamamah, Gamal Abdel Naser; Talaat Abdel Alim, Ahmed Ahmed; Mostafa, Yehia Salah El Din; Ahmed, Rania Ahmed Abdel Salam; Mohammed, Asmaa Mahmoud; Mahmoud, Asmaa Mohammed

2015-01-01

To assess the prevalence and causes of visual impairment in children of South Sinai, and to evaluate outcomes of rehabilitation programs. Population-based, cross-sectional analysis of 2070 healthy school children screened for visual impairment from 2009 through 2010 in cities of South Sinai and their surrounding Bedouin settlements. Visual acuity (VA) was tested using Snellen charts followed by cycloplegic autorefractometry for cases with presenting VA ≤ 6/9. Appropriate eyeglasses were prescribed and VA re-evaluated. This study included 1047 boys and 1023 girls, mean age 10.7 ± 3.1 years. Visual impairment (uncorrected VA ≤ 6/9) was detected in 29.4% of children, while 2.0% had moderate-severe visual impairment (uncorrected VA ≤ 6/24). There were statistically significant differences in prevalence of visual impairment between the studied cities (p visual impairment was significantly higher among girls (p children showed significantly lower prevalences of visual impairment. Only age was a reliable predictor of visual impairment (odds ratio 0.94, p children who received spectacles (p children had some form of visual impairment, 90.32% of which comprised refractive errors (mainly astigmatism) which were significantly corrected with eyeglasses. VA screening and correction of refractive errors are of the utmost importance for ensuring better visual outcomes and improved school performance.

Seismic refraction survey of the ANS preferred site

Energy Technology Data Exchange (ETDEWEB)

Davis, R.K. (Automated Sciences Group, Inc., Oak Ridge, TN (United States)); Hopkins, R.A. (Marrich, Inc., Knoxville, TN (United States)); Doll, W.E. (Oak Ridge National Lab., TN (United States))

1992-02-01

Between September 19, 1991 and October 8, 1991 personnel from Martin Marietta Energy Systems, Inc. (Energy Systems), Automated Sciences Group, Inc., and Marrich, Inc. performed a seismic refraction survey at the Advanced Neutron Source (ANS) preferred site. The purpose of this survey was to provide estimates of top-of-rock topography, based on seismic velocities, and to delineate variations in rock and soil velocities. Forty-four seismic refraction spreads were shot to determine top-of-rock depths at 42 locations. Nine of the seismic spreads were shot with long offsets to provide 216 top-of-rock depths for 4 seismic refraction profiles. The refraction spread locations were based on the grid for the ANS Phase I drilling program. Interpretation of the seismic refraction data supports the assumption that the top-of-rock surface generally follows the local topography. The shallow top-of-rock interface interpreted from the seismic refraction data is also supported by limited drill information at the site. Some zones of anomalous data are present that could be the result of locally variable weathering, a localized variation in shale content, or depth to top-of-rock greater than the site norm.

On the effective refractive index of blood

Science.gov (United States)

Nahmad-Rohen, Alexander; Contreras-Tello, Humberto; Morales-Luna, Gesuri; García-Valenzuela, Augusto

2016-01-01

We calculated the real and imaginary parts of the effective refractive index {n}{eff} of blood as functions of wavelength from 400 to 800 nm; we employed van de Hulst’s theory, together with the anomalous diffraction approximation, for the calculation. We modelled blood as a mixture of plasma and erythrocytes. Our results indicate that erythrocyte orientation has a strong effect on {n}{eff}, making blood an optically anisotropic medium except when the erythrocytes are randomly oriented. In the case in which their symmetry axis is perpendicular to the wave vector, {n}{eff} equals the refractive index of plasma at certain wavelengths. Furthermore, the erythrocytes’ shape affects their contribution to {n}{eff} in an important way, implying that studies on the effective refractive index of blood should avoid approximating them as spheres or spheroids. Finally, the effective refractive index of blood predicted by van de Hulst’s theory is different from what would be obtained by averaging the refractive indices of its constituents weighted by volume; such a volume-weighted average is appropriate only for haemolysed blood. We then measured the real part of the refractive index of various blood solutions using two different experimental setups. One of the most important results of our expriment is that {n}{eff} is measurable to a good degree of precision even for undiluted blood, although not all measuring apparatuses are appropriate. The experimental data is self-consistent and in reasonable agreement with our theoretical calculations.

Light rays in gravitating, refractive media

International Nuclear Information System (INIS)

Noonan, T.W.

1982-01-01

The field-to-particle method of H. P. Robertson is applied to the general-relativistic Maxwell equations in order to obtain the general-relativistic equation of motion for a photon in a refractive medium. For the special case of an uncharged, refractive, spherically symmetric mass, the exact first-order differential equation for the light-ray path is given

REFRACTIVE ERROR STATUS IN BAYELSA STATE, NIGERIA

African Journals Online (AJOL)

LIVINGSTON

deepening poverty because of their inability to see well” . In 2002, the .... all the refractions) and other health workers. During the period .... To the best of our knowledge, there is no ... 2020 and eliminate uncorrected refractive error within the ...

Evidence for subwavelength imaging with positive refraction

OpenAIRE

Ma, Yun Gui; Sahebdivan, Sahar; Ong, C. K.; Tyc, Tomas; Leonhardt, Ulf

2011-01-01

The resolution of lenses is normally limited by the wave nature of light. Imaging with perfect resolution was believed to rely on negative refraction, but here we present experimental evidence for subwavelength imaging with positive refraction. Publisher PDF Peer reviewed

Effect of refractive error on temperament and character properties

Institute of Scientific and Technical Information of China (English)

Emine; Kalkan; Akcay; Fatih; Canan; Huseyin; Simavli; Derya; Dal; Hacer; Yalniz; Nagihan; Ugurlu; Omer; Gecici; Nurullah; Cagil

2015-01-01

AIM: To determine the effect of refractive error on temperament and character properties using Cloninger’s psychobiological model of personality.METHODS: Using the Temperament and Character Inventory(TCI), the temperament and character profiles of 41 participants with refractive errors(17 with myopia,12 with hyperopia, and 12 with myopic astigmatism) were compared to those of 30 healthy control participants.Here, temperament comprised the traits of novelty seeking, harm-avoidance, and reward dependence, while character comprised traits of self-directedness,cooperativeness, and self-transcendence.RESULTS: Participants with refractive error showed significantly lower scores on purposefulness,cooperativeness, empathy, helpfulness, and compassion(P <0.05, P <0.01, P <0.05, P <0.05, and P <0.01,respectively).CONCLUSION: Refractive error might have a negative influence on some character traits, and different types of refractive error might have different temperament and character properties. These personality traits may be implicated in the onset and/or perpetuation of refractive errors and may be a productive focus for psychotherapy.

Perfect imaging without negative refraction

OpenAIRE

Leonhardt, Ulf

2009-01-01

Perfect imaging has been believed to rely on negative refraction, but here we show that an ordinary positively-refracting optical medium may form perfect images as well. In particular, we establish a mathematical proof that Maxwell's fish eye in two-dimensional integrated optics makes a perfect instrument with a resolution not limited by the wavelength of light. We also show how to modify the fish eye such that perfect imaging devices can be made in practice. Our method of perfect focusing ma...

Dispersion characteristics of negative refraction sonic crystals

International Nuclear Information System (INIS)

Wu, L.-Y.; Chen, L.-W.; Wang, R.C.-C.

2008-01-01

Dispersion characteristics of negative refraction sonic crystals are investigated. The plane wave expansion method is used to calculate the equifrequency surface; the dependences of refractive direction on frequencies and incident angles for triangular lattices are shown. There exist the positive and negative refractive waves which include k.V g ≥0 and k.V g ≤0 in the second band for the triangular system. We also use the finite element method to demonstrate that the relative intensity of the transmitted acoustic waves is dependent on incident frequencies and angles. The positions of the partial band gaps obtained by the plane wave expansion method are in good agreement with those obtained by the finite element method. The sonic crystals with negative effective index are shown to have higher transmission intensities. By using the negative refraction behavior, we can design a sonic crystal plane lens to focus a sonic wave

Refractive index inhomogeneity within an aerogel block

International Nuclear Information System (INIS)

Bellunato, T.; Calvi, M.; Da Silva Costa, C.F.; Matteuzzi, C.; Musy, M.; Perego, D.L.

2006-01-01

Evaluating local inhomogeneities of the refractive index inside aerogel blocks to be used as Cherenkov radiator is important for a high energy physics experiment where angular resolution is crucial. Two approaches are described and compared. The first one is based on the bending of a laser beam induced by refractive index gradients along directions normal to the unperturbed optical path. The second method exploits the Cherenkov effect itself by shooting an ultra-relativistic collimated electron beam through different points of the aerogel surface. Local refractive index variations result in sizable differences in the Cherenkov photons distribution

Cryogenic refractive index of Heraeus homosil glass

Science.gov (United States)

Miller, Kevin H.; Quijada, Manuel A.; Leviton, Douglas B.

2017-08-01

This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.34—3.16 μm and temperature range of 120—335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASA's Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a fieldwidened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitive performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dn/dT) and dispersion relation (dn/dλ) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in the literature.

Plasmon-negative refraction at the heterointerface of graphene sheet arrays.

Science.gov (United States)

Huang, He; Wang, Bing; Long, Hua; Wang, Kai; Lu, Peixiang

2014-10-15

We demonstrate negative refraction of surface plasmon polaritons (SPPs) at the heterointerface of two monolayer graphene sheet arrays (MGSAs) with different periods. The refraction angle is specifically related to the period ratio of the two MGSAs. By varying the incident Bloch momentum, the SPPs might be refracted in the direction normal to the heterointerface. Moreover, both positive and negative refraction could appear simultaneously. Because of the linear diffraction relation, the incident and refracted SPP beams experience diffraction-free propagation. The heterostructures composed of the MGSAs may find great applications in deep-subwavelength spatial light modulators, optical splitters, and switches.

Refractive index as materials property. Der Brechungsindex als Stoffeigenschaft

Energy Technology Data Exchange (ETDEWEB)

Zilian, U. (Ciba-Geigy AG, Basel (Switzerland))

1991-10-01

The investigation of the relationship between refractive index (n) and molecular structure of a series of gases, liquids, and solids led to the conclusion that the refractive index of a substance is an independent molecular property. Light is refracted by two types of electron pairs. a) Bonding Electron Pairs (BEP) and b) Response Electron Pairs (REP). - Paraffins exhibit only BEPs which can easily be counted. REP is a new term we introduce to quantify the effects of several nonbonding electrons. The inert gases, for example, refract solely with REPs. They can be determined, and the most important ones are herein tabulated or delineated in the text. For compounds with known formular weight (M) and density (d), the refractive index can be simply calculated using the following formula. (orig.).

Measurements of photoinduced refractive index changes in ...

Indian Academy of Sciences (India)

Abstract. We report the pump–probe measurements of nonlinear refractive index changes in photochromic bacteriorhodopsin films. The photoinduced absorption is caused by pump beam at 532 nm and the accompanying refractive index changes are studied using a probe beam at 633 nm. The proposed technique is ...

Refractive index inversion based on Mueller matrix method

Science.gov (United States)

Fan, Huaxi; Wu, Wenyuan; Huang, Yanhua; Li, Zhaozhao

2016-03-01

Based on Stokes vector and Jones vector, the correlation between Mueller matrix elements and refractive index was studied with the result simplified, and through Mueller matrix way, the expression of refractive index inversion was deduced. The Mueller matrix elements, under different incident angle, are simulated through the expression of specular reflection so as to analyze the influence of the angle of incidence and refractive index on it, which is verified through the measure of the Mueller matrix elements of polished metal surface. Research shows that, under the condition of specular reflection, the result of Mueller matrix inversion is consistent with the experiment and can be used as an index of refraction of inversion method, and it provides a new way for target detection and recognition technology.

Theoretical analyses of the refractive implications of transepithelial PRK ablations.

Science.gov (United States)

Arba Mosquera, Samuel; Awwad, Shady T

2013-07-01

To analyse the refractive implications of single-step, transepithelial photorefractive keratectomy (TransPRK) ablations. A simulation for quantifying the refractive implications of TransPRK ablations has been developed. The simulation includes a simple modelling of corneal epithelial profiles, epithelial ablation profiles as well as refractive ablation profiles, and allows the analytical quantification of the refractive implications of TransPRK in terms of wasted tissue, achieved optical zone (OZ) and induced refractive error. Wasted tissue occurs whenever the actual corneal epithelial profile is thinner than the applied epithelial ablation profile, achieved OZ is reduced whenever the actual corneal epithelial profile is thicker than the applied epithelial ablation profile and additional refractive errors are induced whenever the actual difference centre-to-periphery in the corneal epithelial profile deviates from the difference in the applied epithelial ablation profile. The refractive implications of TransPRK ablations can be quantified using simple theoretical simulations. These implications can be wasted tissue (∼14 µm, if the corneal epithelial profile is thinner than the ablated one), reduced OZ (if the corneal epithelial profile is thicker than ablated one, very severe for low corrections) and additional refractive errors (∼0.66 D, if the centre-to-periphery progression of the corneal epithelial profile deviates from the progression of the ablated one). When TransPRK profiles are applied to normal, not previously treated, non-pathologic corneas, no specific refractive implications associated to the transepithelial profile can be anticipated; TransPRK would provide refractive outcomes equal to those of standard PRK. Adjustments for the planned OZ and, in the event of retreatments, for the target sphere can be easily derived.

Influence of changes in an eye's optical system on refraction

Science.gov (United States)

Bartkowska, Janina

1998-10-01

The optical system of eye is composed of cornea, lens, anterior chamber, and vitreous body. In the standard schematic eye there are 6 refracting surfaces. The changes of the curvature radii, of the distances between them, of the refractive indices influence the ametropia, refractive power of the eye and retinal image size. The influence of these changes can be appreciated by ray tracing or by an analytical method. There are presented simplified formulae for the differentials of ametropia and refractive power of the eye with respect to the surfaces curvatures, refracting power of cornea and lens, refractive indices. The relations are valid too for bigger changes if ametropia is measured in the cornea vertex. The formulae for the differentials with respect to distances, lens translation, eye axis length are valid if ametropia is measured in the object focus of the eye.

Conical Refraction: new observations and a dual cone model.

Science.gov (United States)

Sokolovskii, G S; Carnegie, D J; Kalkandjiev, T K; Rafailov, E U

2013-05-06

We propose a paraxial dual-cone model of conical refraction involving the interference of two cones of light behind the exit face of the crystal. The supporting experiment is based on beam selecting elements breaking down the conically refracted beam into two separate hollow cones which are symmetrical with one another. The shape of these cones of light is a product of a 'competition' between the divergence caused by the conical refraction and the convergence due to the focusing by the lens. The developed mathematical description of the conical refraction demonstrates an excellent agreement with experiment.

Precision measurements of gas refractivity by means of a Fabry-Perot interferometer illustrated by the monitoring of radiator refractivity in the DELPHI RICH detectors

CERN Document Server

Filippas-Tassos, A; Fokitis, E; Maltezos, S; Patrinos, K

2002-01-01

With an updated, flexible, highly efficient and easily installed system we obtained accurate refractivity (n-1) values. This system is a refractometer based on a Fabry-Perot interferometer and was used to monitor the refractivity of DELPHI RICH Cherenkov radiators near the VUV region. By using a Pt-Ne spectral lamp and improved alignment and temperature control, the refractivities of C//5F//1//2 and C//4F//1 //0 have been monitored since 1996. With this light source, selected to have large coherence lengths, we can extract the refractivity at several wavelengths from one data set only. The estimated errors of the refractivity measurements are less than 1.2%, and depend on wavelength and the type of gas used. The various parameters affecting the accuracy of the refractometer are also discussed. Finally, results from special sample refractivity measurements of the liquid radiator (C//6F//1//4) in its gas phase, are presented.

Fermat's principle and the formal equivalence of local light-ray rotation and refraction at the interface between homogeneous media with a complex refractive index ratio.

Science.gov (United States)

Sundar, Bhuvanesh; Hamilton, Alasdair C; Courtial, Johannes

2009-02-01

We derive a formal description of local light-ray rotation in terms of complex refractive indices. We show that Fermat's principle holds, and we derive an extended Snell's law. The change in the angle of a light ray with respect to the normal of a refractive index interface is described by the modulus of the refractive index ratio; the rotation around the interface normal is described by the argument of the refractive index ratio.

Topography-modified refraction: adjustment of treated cylinder amount and axis to the topography versus standard clinical refraction in myopic topography-guided LASIK

OpenAIRE

Alpins, Noel

2017-01-01

Noel Alpins1,2 1NewVision Clinics, Melbourne, VIC, Australia; 2Department Ophthalmology, Melbourne University, Melbourne, VIC, Australia It is encouraging to see the results in the article by Kanellopoulos “Topography-modified refraction (TMR): adjustment of treated cylinder amount and axis to the topography versus standard clinical refraction in myopic topography-guided LASIK”,1 where the combination of refractive and corneal data in the treatment parameters pro...

Optical negative refraction by four-wave mixing in thin metallic nanostructures.

Science.gov (United States)

Palomba, Stefano; Zhang, Shuang; Park, Yongshik; Bartal, Guy; Yin, Xiaobo; Zhang, Xiang

2011-10-30

The law of refraction first derived by Snellius and later introduced as the Huygens-Fermat principle, states that the incidence and refracted angles of a light wave at the interface of two different materials are related to the ratio of the refractive indices in each medium. Whereas all natural materials have a positive refractive index and therefore exhibit refraction in the positive direction, artificially engineered negative index metamaterials have been shown capable of bending light waves negatively. Such a negative refractive index is the key to achieving a perfect lens that is capable of imaging well below the diffraction limit. However, negative index metamaterials are typically lossy, narrow band, and require complicated fabrication processes. Recently, an alternative approach to obtain negative refraction from a very thin nonlinear film has been proposed and experimentally demonstrated in the microwave region. However, such approaches use phase conjugation, which makes optical implementations difficult. Here, we report a simple but different scheme to demonstrate experimentally nonlinear negative refraction at optical frequencies using four-wave mixing in nanostructured metal films. The refractive index can be designed at will by simply tuning the wavelengths of the interacting waves, which could have potential impact on many important applications, such as superlens imaging.

[Incidence of refractive errors with corrective aids subsequent selection].

Science.gov (United States)

Benes, P; Synek, S; Petrová, S; Sokolová, Sidlová J; Forýtková, L; Holoubková, Z

2012-02-01

This study follows the occurrence of refractive errors in population and the possible selection of the appropriate type of corrective aids. Objective measurement and subsequent determination of the subjective refraction of the eye is on essential act in opotmetric practice. The file represented by 615 patients (1230 eyes) is divided according to the refractive error of myopia, hyperopia and as a control group are listed emetropic clients. The results of objective and subjective values of refraction are compared and statistically processed. The study included 615 respondents. To determine the objective refraction the autorefraktokeratometer with Placido disc was used and the values of spherical and astigmatic correction components, including the axis were recorded. These measurements were subsequently verified and tested subjectively using the trial lenses and the projection optotype to the normal investigative distance of 5 meters. After this the appropriate corrective aids were then recommended. Group I consists of 123 men and 195 women with myopia (n = 635) of clients with an average age 39 +/- 18,9 years. Objective refraction - sphere: -2,57 +/- 2,46 D, cylinder: -1,1 +/- 1,01 D, axis of: 100 degrees +/- 53,16 degrees. Subjective results are as follows--the value of sphere: -2,28 +/- 2,33 D, cylinder -0,63 +/- 0,80 D, axis of: 99,8 degrees +/- 56,64 degrees. Group II is represented hyperopic clients and consists of 67 men and 107 women (n = 348). The average age is 58,84 +/- 16,73 years. Objective refraction has values - sphere: +2,81 +/- 2,21 D, cylinder: -1,0 +/- 0,94 D; axis 95 degree +/- 45,4 degrees. Subsequent determination of subjective refraction has the following results - sphere: +2,28 +/- 2,06 D; cylinder: -0,49 +/- 0,85 D, axis of: 95,9 degrees +/- 46,4 degrees. Group III consists from emetropes whose final minimum viasual acuity was Vmin = 1,0 (5/5) or better. Overall, this control group is represented 52 males and 71 females (n = 247). The average

Acoustic metasurface for refracted wave manipulation

Science.gov (United States)

Han, Li-Xiang; Yao, Yuan-Wei; Zhang, Xin; Wu, Fu-Gen; Dong, Hua-Feng; Mu, Zhong-Fei; Li, Jing-bo

2018-02-01

Here we present a design of a transmitted acoustic metasurface based on a single row of Helmholtz resonators with varying geometric parameters. The proposed metasurface can not only steer an acoustic beam as expected from the generalized Snell's law of refraction, but also exhibits various interesting properties and potential applications such as insulation of two quasi-intersecting transmitted sound waves, ultrasonic Bessel beam generator, frequency broadening effect of anomalous refraction and focusing.

Crystalline lens and refractive development.

Science.gov (United States)

Iribarren, Rafael

2015-07-01

Individual refractive errors usually change along lifespan. Most children are hyperopic in early life. This hyperopia is usually lost during growth years, leading to emmetropia in adults, but myopia also develops in children during school years or during early adult life. Those subjects who remain emmetropic are prone to have hyperopic shifts in middle life. And even later, at older ages, myopic shifts are developed with nuclear cataract. The eye grows from 15 mm in premature newborns to approximately 24 mm in early adult years, but, in most cases, refractions are maintained stable in a clustered distribution. This growth in axial length would represent a refractive change of more than 40 diopters, which is compensated by changes in corneal and lens powers. The process which maintains the balance between the ocular components of refraction during growth is still under study. As the lens power cannot be measured in vivo, but can only be calculated based on the other ocular components, there have not been many studies of lens power in humans. Yet, recent studies have confirmed that the lens loses power during growth in children, and that hyperopic and myopic shifts in adulthood may be also produced by changes in the lens. These studies in children and adults give a picture of the changing power of the lens along lifespan. Other recent studies about the growth of the lens and the complexity of its internal structure give clues about how these changes in lens power are produced along life. Copyright © 2015 Elsevier Ltd. All rights reserved.

High temperature refractive indices of GaN

Energy Technology Data Exchange (ETDEWEB)

Liu, C.; Stepanov, S.; Gott, A.; Shields, P.A.; Zhirnov, E.; Wang, W.N. [Department of Physics, University of Bath, Bath, BA2 7AY (United Kingdom); Steimetz, E.; Zettler, J.T. [LayTec, Helmholtzstr. 13-14, 10587 Berlin (Germany)

2006-06-15

Undoped GaN (u-GaN) films were grown by low pressure metalorganic vapour phase epitaxy (LP-MOVPE) on sapphire substrates. In situ optical monitoring was applied to the growth process either using a LayTec EpiR-DA TT spectroscopic reflectometer or Filmetrics F30. Refractive indices of u-GaN films at 1060 C were obtained in a spectral range from 370-900 nm. A peak at 412{+-}5 nm in refractive index spectra was observed, which most likely corresponds to the band-gap of hexagonal GaN at a temperature of 1060 C. Refractive indices below this band-gap are fitted well to the first-order Sellmeier formula. As an example of the applications of the refractive indices, the effective film thicknesses of GaN during the resumption from 3 dimensional (3D) to 2 dimensional (2D) growth have been calculated from the spectra recorded by a LayTec system using the optical constants obtained. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Bioinspired adaptive gradient refractive index distribution lens

Science.gov (United States)

Yin, Kezhen; Lai, Chuan-Yar; Wang, Jia; Ji, Shanzuo; Aldridge, James; Feng, Jingxing; Olah, Andrew; Baer, Eric; Ponting, Michael

2018-02-01

Inspired by the soft, deformable human eye lens, a synthetic polymer gradient refractive index distribution (GRIN) lens with an adaptive geometry and focal power has been demonstrated via multilayer coextrusion and thermoforming of nanolayered elastomeric polymer films. A set of 30 polymer nanolayered films comprised of two thermoplastic polyurethanes having a refractive index difference of 0.05 were coextruded via forced-assembly technique. The set of 30 nanolayered polymer films exhibited transmission near 90% with each film varying in refractive index by 0.0017. An adaptive GRIN lens was fabricated from a laminated stack of the variable refractive index films with a 0.05 spherical GRIN. This lens was subsequently deformed by mechanical ring compression of the lens. Variation in the optical properties of the deformable GRIN lens was determined, including 20% variation in focal length and reduced spherical aberration. These properties were measured and compared to simulated results by placido-cone topography and ANSYS methods. The demonstration of a solid-state, dynamic focal length, GRIN lens with improved aberration correction was discussed relative to the potential future use in implantable devices.

Experimental refractive index determination of the optic fiber's core

International Nuclear Information System (INIS)

Oezelsoy, S.

2005-01-01

In this work, the Fresnel's fundamental Law was used to be able to obtain the refractive index of the fiber optic's core. The intensity of light reflected from the boundary between two mediums was measured by the optical powermeter (Melles Griot, Universal optical powermeter). In recent technology, the light that is illuminated from the light source can be transported to the boundary region and measured with minimum loss by using the optic fibers which make the measurement more sensitively. The liquid and the optic fiber's core whose refractive indices will be measured are the two mediums and the surface of the optic fiber's core is the boundary region. By dipping the fiber optic probe to the liquids, the reflected light intensities were measured with powermeter via Silicon Detector for single mode fiber and multimode fiber respectively to obtain the refractive index of the optic fiber's core. At this work, because of the using the diode laser with 661,4 nm (FWHM) and He-Ne laser with 632,8 nm (FWHM) the refractive indices were measured at this wavelengthes with the Refractometer (Abbe 60-70, Bellingham+Stanley). If the refractive indices of two mediums are equal, the light doesn't reflect from the boundary. The graphic is drawn depend upon the refractive index of the liquids versus the back reflected light energy and from the minimum point of the curve the effective refractive index of the fiber optic's core is calculated for 661,4 nm and 780 nm

Black and gray Helmholtz-Kerr soliton refraction

International Nuclear Information System (INIS)

Sanchez-Curto, Julio; Chamorro-Posada, Pedro; McDonald, Graham S.

2011-01-01

Refraction of black and gray solitons at boundaries separating different defocusing Kerr media is analyzed within a Helmholtz framework. A universal nonlinear Snell's law is derived that describes gray soliton refraction, in addition to capturing the behavior of bright and black Kerr solitons at interfaces. Key regimes, defined by beam and interface characteristics, are identified, and predictions are verified by full numerical simulations. The existence of a unique total nonrefraction angle for gray solitons is reported; both internal and external refraction at a single interface is shown possible (dependent only on incidence angle). This, in turn, leads to the proposal of positive or negative lensing operations on soliton arrays at planar boundaries.

THE OPTICS OF REFRACTIVE SUBSTRUCTURE

Energy Technology Data Exchange (ETDEWEB)

Johnson, Michael D.; Narayan, Ramesh, E-mail: mjohnson@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2016-08-01

Newly recognized effects of refractive scattering in the ionized interstellar medium have broad implications for very long baseline interferometry (VLBI) at extreme angular resolutions. Building upon work by Blandford and Narayan, we present a simplified, geometrical optics framework, which enables rapid, semi-analytic estimates of refractive scattering effects. We show that these estimates exactly reproduce previous results based on a more rigorous statistical formulation. We then derive new expressions for the scattering-induced fluctuations of VLBI observables such as closure phase, and we demonstrate how to calculate the fluctuations for arbitrary quantities of interest using a Monte Carlo technique.

Analytical models of optical refraction in the troposphere.

Science.gov (United States)

Nener, Brett D; Fowkes, Neville; Borredon, Laurent

2003-05-01

An extremely accurate but simple asymptotic description (with known error) is obtained for the path of a ray propagating over a curved Earth with radial variations in refractive index. The result is sufficiently simple that analytic solutions for the path can be obtained for linear and quadratic index profiles. As well as rendering the inverse problem trivial for these profiles, this formulation shows that images are uniformly magnified in the vertical direction when viewed through a quadratic refractive-index profile. Nonuniform vertical distortions occur for higher-order refractive-index profiles.

Ultraviolet light induced refractive index structures in germanosilica

DEFF Research Database (Denmark)

Svalgaard, Mikael

1997-01-01

The focus of the research presented in this ph.d. thesis is refractive index structures photoinduced in germanonsilica waveguides with ultra-violet (UV) radiation. The physical mechanisms involved in photosensitivity and applications of a wide range of UV induced refractive index structures in both...... application of a scanning near-field optical microscope to obtain high resolution images of UV induced refractive index structures and by monitoring the dynamics of UV induced index changes and luminescence. During part of my ph.d. project I have worked at the National Institute of Standards and Technolgy...

refractive errors among secondary school students in Isuikwuato

African Journals Online (AJOL)

Eyamba

STUDENTS IN ISUIKWUATO LOCAL GOVERNMENT AREA OF ... the prevalence and types of refractive errors among secondary school students ... KEYWORDS: Refractive error, Secondary School students, ametropia, .... interviews of the teachers as regards the general performance of those students with obvious visual.

Refractive Lenticule Implantation for Correction of Ametropia: Case Reports and Literature Review.

Science.gov (United States)

Lazaridis, A; Messerschmidt-Roth, A; Sekundo, W; Schulze, S

2017-01-01

The ReLEx® technique allows correction of refractive errors through the creation and extraction of refractive stromal lenticules. Contrary to excimer laser corneal refractive procedures, where the stromal tissue is photoablated, the extracted lenticules obtained with ReLEx® can be preserved. Recent studies and case reports have described autologous re-implantation and allogeneic implantation of refractive lenticules into femtosecond-laser created stromal pockets in order to reverse the refractive outcome of a myopic corneal refractive procedure, correct hyperopia, aphakia, presbyopia and treat keratoconus. The use of stromal lenticules has also been described for therapeutic purposes, with an allogenic lenticule being transplanted under a LASIK flap in order to restore corneal volume and reduce the refractive error in a case of excessive stromal tissue removal after LASIK. This review summarises the results of the latest case reports and studies that describe the implantation of cryopreserved or fresh refractive stromal lenticules and discusses the feasibility, safety and refractive outcomes of the procedure, on the basis of published literature as well as our own experience. Georg Thieme Verlag KG Stuttgart · New York.

Estimation of network parameters with consideration of the horizontal refraction influence

Directory of Open Access Journals (Sweden)

Ján Ježko

2007-06-01

Full Text Available The proposed paper is focused on reviewing the horizontal refraction during measurement in local geodetic networks. Based on elaborated theoretical assumptions the refraction model was arranged in a way that the questions were solved by the identity of the horizontal refraction. The necessary part of the application of the refraction model is the problem of optimizing the geodetic networks and deducting the method of the variance components, which play a major role in the precision of results. The independent acquisition of the thesis lies in the area of modeling the horizontal refraction with a stochastic approach, where the values of the refraction are gained through the measured data of the horizontal direction. In the model, it is necessary to identify the parameters according to the entire measurements and between two points. According to the attained results, I can state that the horizontal refraction was identified mainly on the measurements that were confirmed near the dam in most of the measured experiments. The experimented measurements were confirmed based on the assumptions that are in theoretical capitol, where the assumptions of the effect of the horizontal refraction are measured near the dam, river, shores, and valleys.

Pressure-dependent refractive indices of gases by THz time-domain spectroscopy.

Science.gov (United States)

Sang, Bark Hyeon; Jeon, Tea-In

2016-12-12

Noncontact terahertz time-domain spectroscopy was employed to measure pressure-dependent refractive indices of gases such as helium (He), argon (Ar), krypton (Kr), oxygen (O2), nitrogen (N2), methane (CH4), and carbon dioxide (CO2). The refractive indices of these gases scaled linearly with pressure, for pressures in the 55-3,750 torr range. At the highest pressure, the refractive indices ((n-1) x 106) of He and CO2 were 170 and 2,390, respectively. The refractive index of CO2 was 14.1-fold higher than that of He, owing to the stronger polarizability of CO2. Although the studied gases differed in terms of their molecular structure, their refractive indices were strongly determined by polarizability. The measured refractive indices agreed well with the theoretical calculations.

Nanofocusing refractive X-ray lenses

Energy Technology Data Exchange (ETDEWEB)

Boye, Pit

2010-02-05

This thesis is concerned with the optimization and development of the production of nanofocusing refractive X-ray lenses. These optics made of either silicon or diamond are well-suited for high resolution X-ray microscopy. The goal of this work is the design of a reproducible manufacturing process which allows the production of silicon lenses with high precision, high quality and high piece number. Furthermore a process for the production of diamond lenses is to be developed and established. In this work, the theoretical basics of X-rays and their interaction with matter are described. Especially, aspects of synchrotron radiation are emphasized. Important in X-ray microscopy are the different optics. The details, advantages and disadvantages, in particular those of refractive lenses are given. To achieve small X-ray beams well beyond the 100 nm range a small focal length is required. This is achieved in refractive lenses by moving to a compact lens design where several single lenses are stacked behind each other. The, so-called nanofocusing refractive lenses (NFLs) have a parabolic cylindrical shape with lateral structure sizes in the micrometer range. NFLs are produced by using micro-machining techniques. These micro-fabrication processes and technologies are introduced. The results of the optimization and the final fabrication process for silicon lenses are presented. Subsequently, two experiments that are exemplary for the use of NFLs, are introduced. The rst one employs a high-resolution scanning fluorescence mapping of a geological sample, and the second one is a coherent x-ray diffraction imaging (CXDI) experiment. CXDI is able to reconstruct the illuminated object from recorded coherent diffraction patterns. In a scanning mode, referred to as ptychography, this method is even able to reconstruct the illumination and the object simultaneously. Especially the reconstructed illumination and the possibility of computed propagation of the wave field along the

Nanofocusing refractive X-ray lenses

International Nuclear Information System (INIS)

Boye, Pit

2010-01-01

This thesis is concerned with the optimization and development of the production of nanofocusing refractive X-ray lenses. These optics made of either silicon or diamond are well-suited for high resolution X-ray microscopy. The goal of this work is the design of a reproducible manufacturing process which allows the production of silicon lenses with high precision, high quality and high piece number. Furthermore a process for the production of diamond lenses is to be developed and established. In this work, the theoretical basics of X-rays and their interaction with matter are described. Especially, aspects of synchrotron radiation are emphasized. Important in X-ray microscopy are the different optics. The details, advantages and disadvantages, in particular those of refractive lenses are given. To achieve small X-ray beams well beyond the 100 nm range a small focal length is required. This is achieved in refractive lenses by moving to a compact lens design where several single lenses are stacked behind each other. The, so-called nanofocusing refractive lenses (NFLs) have a parabolic cylindrical shape with lateral structure sizes in the micrometer range. NFLs are produced by using micro-machining techniques. These micro-fabrication processes and technologies are introduced. The results of the optimization and the final fabrication process for silicon lenses are presented. Subsequently, two experiments that are exemplary for the use of NFLs, are introduced. The rst one employs a high-resolution scanning fluorescence mapping of a geological sample, and the second one is a coherent x-ray diffraction imaging (CXDI) experiment. CXDI is able to reconstruct the illuminated object from recorded coherent diffraction patterns. In a scanning mode, referred to as ptychography, this method is even able to reconstruct the illumination and the object simultaneously. Especially the reconstructed illumination and the possibility of computed propagation of the wave field along the

Accommodation, refractive error and eye growth in chickens.

Science.gov (United States)

Schaeffel, F; Glasser, A; Howland, H C

1988-01-01

We raised chickens with defocusing lenses of differing powers in front of their eyes. For this purpose, small hoods made from soft, thin leather were carefully fitted to their heads. Lenses were attached to the hoods by velcro fasteners and could be easily removed for cleaning. The powers of the lenses were such that their optical effects could be compensated for by accommodation. It was verified by infrared (IR) photoretinoscopy that the chickens could keep their retinal images in focus. Wearing a lens resulted in a consistent shift of the non cycloplegic refractive state (measured without the lens) which was in the direction to compensate for the lens. We used a sensitive technique (precision = +/- 50 micron as estimated from the variability of repeated measurements) to measure the posterior nodal distance (PND) in excised eyes of birds grown with lenses. The PND, in turn, was used to compare eyes treated with different lenses. It was found that the PND was increased in eyes which were treated with negative lenses compared to those treated with positive lenses. This effect occurs independently in both eyes and it is not due to changes in corneal curvature. We discuss our result in terms of a closed-loop feedback system for the regulation of eye growth.

Measurement of Refractive Index Using a Michelson Interferometer.

Science.gov (United States)

Fendley, J. J.

1982-01-01

Describes a novel and simple method of measuring the refractive index of transparent plates using a Michelson interferometer. Since it is necessary to use a computer program when determining the refractive index, undergraduates could be given the opportunity of writing their own programs. (Author/JN)

Perfect imaging without negative refraction

Energy Technology Data Exchange (ETDEWEB)

Leonhardt, Ulf [School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom)], E-mail: ulf@st-andrews.ac.uk

2009-09-15

Perfect imaging has been believed to rely on negative refraction, but here we show that an ordinary positively refracting optical medium may form perfect images as well. In particular, we establish a mathematical proof that Maxwell's fish eye in two-dimensional (2D) integrated optics makes a perfect instrument with a resolution not limited by the wavelength of light. We also show how to modify the fish eye such that perfect imaging devices can be made in practice. Our method of perfect focusing may also find applications outside of optics, in acoustics, fluid mechanics or quantum physics, wherever waves obey the 2D Helmholtz equation.

On the optical path length in refracting media

Science.gov (United States)

Hasbun, Javier E.

2018-04-01

The path light follows as it travels through a substance depends on the substance's index of refraction. This path is commonly known as the optical path length (OPL). In geometrical optics, the laws of reflection and refraction are simple examples for understanding the path of light travel from source to detector for constant values of the traveled substances' refraction indices. In more complicated situations, the Euler equation can be quite useful and quite important in optics courses. Here, the well-known Euler differential equation (EDE) is used to obtain the OPL for several index of refraction models. For pedagogical completeness, the OPL is also obtained through a modified Monte Carlo (MC) method, versus which the various results obtained through the EDE are compared. The examples developed should be important in projects involving undergraduate as well as graduate students in an introductory optics course. A simple matlab script (program) is included that can be modified by students who wish to pursue the subject further.

Photorefractive keratectomy in refractive accommodative esotropia.

Science.gov (United States)

Bilgihan, K; Akata, F; Or, M; Hasanreisoğlu, B

1997-01-01

Photorefractive keratectomy (PRK) was performed on a 19-year-old man with hyperopic astigmatism and refractive accommodative esotropia. The patient was orthophoric while wearing spectacles, but had an esotropia of 30 prism dioptres at near and distance vision without spectacles. The best corrected visual acuity of the right eye was 20/50 and of the left eye was 20/20. The excessive accommodative convergence of the patient was eliminated by correcting the hyperopic refractive error by performing PRK, and the patient became orthophoric after the treatment.

Refractive Errors in State Junior High School Students in Bandung

Directory of Open Access Journals (Sweden)

Sabila Tasyakur Nikmah

2016-12-01

Full Text Available Background: Uncorrected refractive error is one of the avoidable causes of vision impairment in children and adults. Vision problem in children has been shown to affect their psychological and academic performance. This study aims at identifying and gaining more insights on the characteristic of the refractive errors in state junior high school students in Bandung to avoid uncorrected refractive errors. Methods: A cross-sectional study was conducted in September–November 2015 in state junior high schools in Bandung, West Java, Indonesia. Sample was selected using multistage random sampling technique. Children were examined using tumbling E examination; then students with visual acuity worse than 6/12 underwent Snellen Chart test, refractometry without pupil dilatation, correction with trial lens, then was followed by direct ophthalmoscopy. Results: From a total of 435 children who completed all the examination, 80 children (18.39% had refractive errors; consisted of 151 eyes (94.38% with myopia and 9 eyes (5.62% with astigmatism. Refractive errors were found to be more common in female children (73.7% than male children (26.3%. Among those with refractive errors, 45 children (56.3% did not use any corrective glasses before the examination. Conclusions: Routine refractive error test in vision screening examination is needed for students. It is equally important to raise more awareness toward eye disease in community.

Atmosphere Refraction Effects in Object Locating for Optical Satellite Remote Sensing Images

Directory of Open Access Journals (Sweden)

YAN Ming

2015-09-01

Full Text Available The collinear rigorous geometric model contains the atmosphere refraction geometric error in off-nadir observation. In order to estimate and correct the atmosphere refraction geometric error, the ISO international standard atmospheric model and Owens atmosphere refractive index algorithm are applied to calculate the index of atmosphere refraction in different latitude and altitude. The paper uses the weighted mean algorithm to reduce the eight layers ISO standard atmospheric model into a simple troposphere and stratosphere two layers spherical atmosphere. And the LOS vector track geometric algorithm is used to estimate the atmosphere refraction geometric error in different observation off-nadir angle. The results show that the atmosphere refraction will introduce about 2.5 m or 9 m geometric displacement in 30 or 45 degree off-nadir angle individual. Therefore, during geo-location processing of agile platform and extra wide high spatial resolution imagery, there is need to take into account the influence of atmosphere refraction and correct the atmosphere refraction geometric error to enhance the geo-location precision without GCPs.

Prevalence of Refractive errors among Primary School Pupils in ...

African Journals Online (AJOL)

Administrator

Effective management of blindness due to refractive errors is readily available in developed countries. 1 ... Key words: Refractive errors, Children, Prevalence, Kenya. 165 .... financial support towards the funding of this study. REFERENCES. 1.

Optical 'dampening' of the refractive error to axial length ratio: implications for outcome measures in myopia control studies.

Science.gov (United States)

Cruickshank, Fiona E; Logan, Nicola S

2018-05-01

To gauge the extent to which differences in the refractive error axial length relationship predicted by geometrical optics are observed in actual refractive/biometric data. This study is a retrospective analysis of existing data. Right eye refractive error [RX] and axial length [AXL] data were collected on 343 6-to-7-year-old children [mean 7.18 years (S.D. 0.35)], 294 12-to-13-year-old children [mean 13.12 years (S.D. 0.32)] and 123 young adults aged 18-to-25-years [mean 20.56 years (S.D. 1.91)]. Distance RX was measured with the Shin-Nippon NVision-K 5001 infrared open-field autorefractor. Child participants were cyclopleged prior to data collection (1% Cyclopentolate Hydrochloride). Myopia was defined as a mean spherical equivalent [MSE] ≤-0.50 D. Axial length was measured using the Zeiss IOLMaster 500. Optical modelling was based on ray tracing and manipulation of parameters of a Gullstrand reduced model eye. There was a myopic shift in mean MSE with age (6-7 years +0.87 D, 12-13 years -0.06 D and 18-25 years -1.41 D), associated with an increase in mean AXL (6-7 years 22.70 mm, 12-13 years 23.49 mm and 18-25 years 23.98 mm). There was a significant negative correlation between MSE and AXL for all age groups (all p theory predicts that there will be a reduction in the RX: AXL ratio with longer eyes. The participant data although adhering to this theory show a reduced effect, with eyes with longer axial lengths having a lower refractive error to axial length ratio than predicted by model eye calculations. We propose that in myopia control intervention studies when comparing efficacy, consideration should be given to the dampening effect seen with a longer eye. © 2018 The Authors. Ophthalmic and Physiological Optics published by John Wiley & Sons Ltd on behalf of College of Optometrists.

Negative refraction of inhomogeneous waves in lossy isotropic media

International Nuclear Information System (INIS)

Fedorov, V Yu; Nakajima, T

2014-01-01

We theoretically study negative refraction of inhomogeneous waves at the interface of lossy isotropic media. We obtain explicit (up to the sign) expressions for the parameters of a wave transmitted through the interface between two lossy media characterized by complex permittivity and permeability. We show that the criterion of negative refraction that requires negative permittivity and permeability can be used only in the case of a homogeneous incident wave at the interface between a lossless and lossy media. In a more general situation, when the incident wave is inhomogeneous, or both media are lossy, the criterion of negative refraction becomes dependent on an incidence angle. Most interestingly, we show that negative refraction can be realized in conventional lossy materials (such as metals) if their interfaces are properly oriented. (paper)

Prevalence of Refractive Error in Singaporean Chinese Children: The Strabismus, Amblyopia, and Refractive Error in Young Singaporean Children (STARS) Study

OpenAIRE

Dirani, Mohamed; Chan, Yiong-Huak; Gazzard, Gus; Hornbeak, Dana Marie; Leo, Seo-Wei; Selvaraj, Prabakaran; Zhou, Brendan; Young, Terri L.; Mitchell, Paul; Varma, Rohit; Wong, Tien Yin; Saw, Seang-Mei

2010-01-01

Using population-based data, the authors report, for the first time, the prevalence of refractive error in Singaporean Chinese children aged 6 to 72 months. In selected regions of Singapore, myopia has been shown to affect more than 80% of adults; therefore, this paper provides insights into the development of refractive error at a very young age.

The effect of spectral property and intensity of light on natural refractive development and compensation to negative lenses in guinea pigs.

Science.gov (United States)

Li, Wentao; Lan, Weizhong; Yang, Shiqi; Liao, Yunru; Xu, Qinglin; Lin, Lixia; Yang, Zhikuan

2014-10-02

To investigate the effect of spectral composition and light intensity on refractive development in guinea pigs. One-week-old guinea pigs were randomly assigned to groups exposed to broad-spectrum Solux halogen light (BS) or spiked-spectrum fluorescent light (FL) at both high (Hi, 10,000 lux) and low (Lo, 500 lux) intensities under a 12:12 light/dark cycle. Half of the animals in each group were used as controls (n = 24, 20, 22, and 20, respectively), and half were fitted with binocular -4-diopter (D) lenses (L, lenses; n = 22, 20, 24, and 22, respectively). Refractive error, corneal curvature, and axial dimensions were determined by cycloplegic retinoscopy, photokeratometry, and A-scan ultrasonography, respectively. Guinea pigs exposed to FL and BS showed similar changes in refraction under both high (HiFL: 2.26 ± 0.55 D versus HiBS: 2.17 ± 0.65 D, P > 0.05)- and low-intensity lighting (LoFL: 1.39 ± 0.88 D versus LoBS: 1.40 ± 0.93 D, P > 0.05). This was also true for the groups wearing lenses (HiFL-L: -1.81 ± 0.73 D versus HiBS-L: -1.45 ± 0.99 D, P > 0.05; LoFL-L: -2.58 ± 0.65 D versus LoBS-L: -2.29 ± 0.50 D, P > 0.05). Nevertheless, animals under high-intensity lighting exhibited a significantly larger hyperopic shift compared with those under low-intensity lighting (HiFL versus LoFL: P development and negative lens compensation. As found in other species, effects of light intensity on refractive development were also observed in guinea pigs in both illuminants. Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc.

Application of seismic refraction tomography for subsurface imaging ...

African Journals Online (AJOL)

Seismic refraction tomography involves the measurement of the travel times of seismic refracted raypaths in order to define an image of seismic velocity in the intervening ground. This technique was used to estimate the depth to the fresh basement, estimate thickness of the weathered basement and to determine the ...

Refractive power and biometric properties of the nonhuman primate isolated crystalline lens.

Science.gov (United States)

Borja, David; Manns, Fabrice; Ho, Arthur; Ziebarth, Noel M; Acosta, Ana Carolina; Arrieta-Quintera, Esdras; Augusteyn, Robert C; Parel, Jean-Marie

2010-04-01

Purpose. To characterize the age dependence of shape, refractive power, and refractive index of isolated lenses from nonhuman primates. Methods. Measurements were performed on ex vivo lenses from cynomolgus monkeys (cyno: n = 120; age, 2.7-14.3 years), rhesus monkeys (n = 61; age, 0.7-13.3 years), and hamadryas baboons (baboon: n = 16; age, 1.7-27.3 years). Lens thickness, diameter, and surface curvatures were measured with an optical comparator. Lens refractive power was measured with a custom optical system based on the Scheiner principle. The refractive contributions of the gradient, the surfaces, and the equivalent refractive index were calculated with optical ray-tracing software. The age dependence of the optical and biometric parameters was assessed. Results. Over the measured age range isolated lens thickness decreased (baboon: -0.04, cyno: -0.05, and rhesus: -0.06 mm/y) and equatorial diameter increased (logarithmically for the baboon and rhesus, and linearly for cyno: 0.07 mm/y). The isolated lens surfaces flattened and the corresponding refractive power from the surfaces decreased with age (-0.33, -0.48, and -0.68 D/y). The isolated lens equivalent refractive index decreased (only significant for the baboon, -0.001 D/y), and as a result the total isolated lens refractive power decreased with age (baboon: -1.26, cyno: -0.97, and rhesus: -1.76 D/y). Conclusions. The age-dependent trends in the optical and biometric properties, growth, and aging, of nonhuman primate lenses are similar to those of the pre-presbyopic human lens. As the lens ages, the decrease in refractive contributions from the gradient refractive index causes a rapid age-dependent decrease in maximally accommodated lens refractive power.

First-principle calculation of refractive indices of BAlN and BGaN

KAUST Repository

Alqatari, Feras; Li, Kuang-Hui; Liu, Kaikai; Li, Xiaohang

2018-01-01

The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.

First-principle calculation of refractive indices of BAlN and BGaN

KAUST Repository

Alqatari, Feras

2018-03-27

The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.

[Nature or nurture: effects of parental ametropia on children's refractive errors].

Science.gov (United States)

Landmann, A; Bechrakis, E

2013-12-01

The aim of this study was to quantify the degree of association between juvenile refraction errors and parental refraction status. Using a simple questionnaire we conducted a cross-sectional study to determine the prevalence and magnitudes of refractive errors and of parental refraction status in a sample (n=728) of 10- to 18-year-old Austrian grammar school students. Students with myopia or hyperopia were more likely to have ametropic parents and refraction was more myopic in juveniles with one or two parents being ametropic. The prevalence of myopia in children with 2 ametropic parents was 54%, decreasing to 35% in pupils with 1 and to 13% in children with no ametropic parents. The odds ratio for 1 and 2 compared with no ametropic parents was 8.3 and 3.7 for myopia and 1.3 and 1.6 for hyperopia, respectively. Furthermore, the data indicate a stronger influence of the maternal ametropia on children's refractive errors than paternal ametropia. Genetic factors play a significant role in refractive error and may be of dominant influence for school myopia under conditions of low environmental variation.

Axial Length/Corneal Radius of Curvature Ratio and Refractive ...

African Journals Online (AJOL)

2017-06-14

Jun 14, 2017 ... of individuals,[2,5-8] the relationship between CR and refractive status ... the relationship between refractive error and ocular .... AG, 07740 Jena Germany). ..... adult population in rural Myanmar: The Meiktila eye study. Clin.

Extraordinary refraction and self-collimation properties of multilayer metallic-dielectric stratified structures

Energy Technology Data Exchange (ETDEWEB)

Zhang, Liwei, E-mail: zlwhpu@hotmail.com [School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000 (China); Chen, Liang [School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000 (China); Zhang, Zhengren [School of Science, Chongqing Jiaotong University, Chongqing 400074 (China); Wang, Wusong [Guizhou Aerospace Institute of Measuring and Testing Technology, Guiyang 550009 (China); Zhao, Yuhuan; Song, Kechao; Kang, Chaoyang [School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000 (China)

2015-01-15

The extraordinary refraction with negative or zero refraction angle of the layered metamaterial consisting of alternating dielectric and plasmonic layers is theoretically studied. It is shown that the electromagnetic properties can be tuned by the filling factor, the permittivity of the dielectric layer and the plasma frequency of the metallic layer. At different frequency, the layered structures possess different refraction properties with positive, zero or negative refraction angle. By choosing appropriate parameters, positive-to-zero-to-negative-to positive refraction at the desired frequency can be realized. At the frequency with flat equal frequency contour, self-collimation and slow light properties are also found. Such properties can be used in the performance of negative refraction, subwavelength imaging and information propagation.

Performance of Photoscreener in Detection of Refractive Error in All Age Groups and Amblyopia Risk Factors in Children in a Tribal District of Odisha: The Tribal Odisha Eye Disease Study (TOES) # 3

Science.gov (United States)

Panda, Lapam; Barik, Umasankar; Nayak, Suryasmita; Barik, Biswajit; Behera, Gyanaranjan; Kekunnaya, Ramesh

2018-01-01

Purpose To evaluate effectiveness of Welch Allyn Spot Vision Screener in detecting refractive error in all age groups and amblyopia risk factors in children in a tribal district of India. Methods All participants received dry retinoscopy and photorefraction; children also received cycloplegic retinoscopy. Statistical analysis included Bland-Altman and coefficient of determination (R2). Results Photoscreener could not elicit a response in 113 adults and 5 children of 580 recruited participants. In Bland-Altman analysis mean difference of Spot screener spherical equivalent (SSSE) and dry retinoscopy spherical equivalent (DRSE) was 0.32 diopters (D) in adults and 0.18 D in children; this was an overestimation of hyperopia and underestimation of myopia. In Bland-Altman analysis of SSSE and cycloplegic retinoscopy spherical equivalent (CRSE) the mean difference was −0.30 D in children; this was an overestimation of myopia and underestimation of hyperopia. In regression analysis the relationship between SSSE and DRSE was poor in adults (R2 = 0.50) and good in children (R2 = 0.92). Cubic regression model for Spot versus cycloretinoscopy in children was: CRSE = 0.34 + 0.85 SSSE − 0.01 SSSE2 + 0.006 SSSE3. It was 87% accurate. Sensitivity and specificity of Spot in detecting amblyopia risk factors (2013 American Association for Pediatric Ophthalmology and Strabismus [AAPOS] criteria) was 93.3% and 96.9% respectively. Sensitivity of Spot screener in detection of amblyopia was 72%. Conclusions Photoscreener has 87% accuracy in refraction in children. Its value could be used for subjective correction tests. Translational Relevance Photoscreening could complement traditional retinoscopy to address refractive error in children in a resource-limited facility region. PMID:29881649

Trends in refractive surgery at an academic center: 2007-2009

Directory of Open Access Journals (Sweden)

Kuo Irene C

2011-05-01

Full Text Available Abstract Background The United States officially entered a recession in December 2007, and it officially exited the recession in December 2009, according to the National Bureau of Economic Research. Since the economy may affect not only the volume of excimer laser refractive surgery, but also the clinical characteristics of patients undergoing surgery, our goal was to compare the characteristics of patients completing excimer laser refractive surgery and the types of procedures performed in the summer quarter in 2007 and the same quarter in 2009 at an academic center. A secondary goal was to determine whether the volume of astigmatism- or presbyopia-correcting intraocular lenses (IOLs has concurrently changed because like laser refractive surgery, these "premium" IOLs involve out-of-pocket costs for patients. Methods Retrospective case series. Medical records were reviewed for all patients completing surgery at the Wilmer Laser Vision Center in the summer quarter of 2007 and the summer quarter of 2009. Outcome measures were the proportions of treated refractive errors, the proportion of photorefractive keratectomy (PRK vs. laser-assisted in-situ keratomileusis (LASIK, and the mean age of patients in each quarter. Chi-square test was used to compare the proportions of treated refractive errors and the proportions of procedures; two-tailed t-test to compare the mean age of patients; and two-tailed z-test to compare proportions of grouped refractive errors in 2007 vs. 2009; alpha = 0.05 for all tests. Refractive errors were grouped by the spherical equivalent of the manifest refraction and were considered "low myopia" for 6 diopters (D of myopia or less, "high myopia" for more than 6 D, and "hyperopia" for any hyperopia. Billing data were reviewed to obtain the volume of premium IOLs. Results Volume of laser refractive procedures decreased by at least 30%. The distribution of proportions of treated refractive errors did not change (p = 0.10. The

Trends in refractive surgery at an academic center: 2007-2009.

Science.gov (United States)

Kuo, Irene C

2011-05-14

The United States officially entered a recession in December 2007, and it officially exited the recession in December 2009, according to the National Bureau of Economic Research. Since the economy may affect not only the volume of excimer laser refractive surgery, but also the clinical characteristics of patients undergoing surgery, our goal was to compare the characteristics of patients completing excimer laser refractive surgery and the types of procedures performed in the summer quarter in 2007 and the same quarter in 2009 at an academic center. A secondary goal was to determine whether the volume of astigmatism- or presbyopia-correcting intraocular lenses (IOLs) has concurrently changed because like laser refractive surgery, these "premium" IOLs involve out-of-pocket costs for patients. Retrospective case series. Medical records were reviewed for all patients completing surgery at the Wilmer Laser Vision Center in the summer quarter of 2007 and the summer quarter of 2009. Outcome measures were the proportions of treated refractive errors, the proportion of photorefractive keratectomy (PRK) vs. laser-assisted in-situ keratomileusis (LASIK), and the mean age of patients in each quarter. Chi-square test was used to compare the proportions of treated refractive errors and the proportions of procedures; two-tailed t-test to compare the mean age of patients; and two-tailed z-test to compare proportions of grouped refractive errors in 2007 vs. 2009; alpha = 0.05 for all tests. Refractive errors were grouped by the spherical equivalent of the manifest refraction and were considered "low myopia" for 6 diopters (D) of myopia or less, "high myopia" for more than 6 D, and "hyperopia" for any hyperopia. Billing data were reviewed to obtain the volume of premium IOLs. Volume of laser refractive procedures decreased by at least 30%. The distribution of proportions of treated refractive errors did not change (p = 0.10). The proportion of high myopes, however, decreased (p = 0

Refraction-contrast bone imaging using synchrotron radiation

International Nuclear Information System (INIS)

Mori, Koichi; Sekine, Norio; Sato, Hitoshi; Shikano, Naoto; Shimao, Daisuke; Shiwaku, Hideaki; Hyodo, Kazuyuki; Oka, Hiroshi

2002-01-01

The X-ray refraction-contrast imaging using synchrotron radiation with some X-ray energies is successfully performed at B120B2 of SPring-8. The refraction-contrast images of bone samples such as human dried proximal phalanx, wrist, upper cervical vertebrae and sella turcica and as mouse proximal femur using the synchrotron X-ray are always better in image contrast and resolution than those of the absorption-contrast images using the synchrotron X-ray and/or the conventional X-ray tube. There is much likeness in the image contrast and resolution of trabeculae bone in the human dried proximal phalanx between X-ray energy of 30 keV at sample-to-film distance of 1 m and those of 40, 50 keV at those of 4,5 m, respectively. High-energy refraction-contrast imaging with suitable sample-to-film distance could reduce the exposure dose in human imaging. In the refraction-contrast imaging of human wrist, upper cervcal vertebrae, sella turcica and mouse proximal femur using the synchrotron X-ray, we can obtain better image contrast and resolution to correctly extract morphological information for diagnosis corresponding to each of the clinical field than those of the absorption-contrast images. (author)

REFRACTIVE ANOMALIES OF AMBLYOPIC CHILDREN WITH AND WITHOUT STRABISMUS

Directory of Open Access Journals (Sweden)

Ljiljana Otašević

2003-04-01

Full Text Available Refractive anomalies occur when the ratio of the refraction ability and the eye length is distrurbed. Amblyopia isunderstood as dimness of vision without detectable lesions of the eye.The aim of the paper is to analyze refractive anomalies occurring in amblyopic children without of with strabismus. The cards of the children suffering from amblyopia and of five of more years of age have been singled out. The number of children obtained in that way is 243. Under special observation were bilateral and unilateral amblyopias and refractive anomalies in children both with and without strabismus. Out of 243 children there are 153 without strabismus (the majority of them reported for examination at the age of seven and 90 with strabismus (the majority of them reported at the age of five. In both the groups bilateral and unilateral amblyopia was registered so that the overall number of the observed amblyopic eyes was 369. In the children without strabismus we mostly found light amblyopia while in the froup of children with strabismus we found, in a great number, medium serious amblyopia while the presence of serious amblypia was also detected. As for refractive anomalies in both the groups of amblyopic children the most freqent were hypermetropic astigmatism and hypermetropia. Because of refractive anomalies as well as with strabismus with small angle, amblyopias are often discovered only when sharpness if vision is being checked; therefore, of great importance are regular systematic examinations of vision sharpness of younger children.

Refractive-Index Sensing with Ultrathin Plasmonic Nanotubes

DEFF Research Database (Denmark)

Raza, Søren; Toscano, Giuseppe; Jauho, Antti-Pekka

2013-01-01

We study the refractive-index sensing properties of plasmonic nanotubes with a dielectric core and ultrathin metal shell. The few nanometer thin metal shell is described by both the usual Drude model and the nonlocal hydrodynamic model to investigate the effects of nonlocality. We derive an analy......We study the refractive-index sensing properties of plasmonic nanotubes with a dielectric core and ultrathin metal shell. The few nanometer thin metal shell is described by both the usual Drude model and the nonlocal hydrodynamic model to investigate the effects of nonlocality. We derive...... an analytical expression for the extinction cross section and show how sensing of the refractive index of the surrounding medium and the figure of merit are affected by the shape and size of the nanotubes. Comparison with other localized surface plasmon resonance sensors reveals that the nanotube exhibits...

Miniature interferometer for refractive index measurement in microfluidic chip

Science.gov (United States)

Chen, Minghui; Geiser, Martial; Truffer, Frederic; Song, Chengli

2012-12-01

The design and development of the miniaturized interferometer for measurement of the refractive index or concentration of sub-microliter volume aqueous solution in microfludic chip is presented. It is manifested by a successful measurement of the refractive index of sugar-water solution, by utilizing a laser diode for light source and the small robust instrumentation for practical implementation. Theoretically, the measurement principle and the feasibility of the system are analyzed. Experimental device is constructed with a diode laser, lens, two optical plate and a complementary metal oxide semiconductor (CMOS). Through measuring the positional changes of the interference fringes, the refractive index change are retrieved. A refractive index change of 10-4 is inferred from the measured image data. The entire system is approximately the size of half and a deck of cards and can operate on battery power for long time.

Creating Materials with Negative Refraction Index using Topology Optimization

DEFF Research Database (Denmark)

Christiansen, Rasmus Ellebæk; Sigmund, Ole

is used for regularizationand a projection step applied to obtain clean 0/1 designs. A continuation scheme is used to avoidstagnation in the optimization. Metamaterials with negative refraction index designed using this method are presented. The angular dependence of the refraction index......We apply topology optimization along with full modeling of the electromagnetic (acoustic) field to create metamaterials with negative refraction index. We believe that our approach can be used in the design of metamaterials with specific effective permittivity and permeability e.g. by adapting....... The direction of propagation for the prescribed wave is chosen to match the angle of incidence of the incoming plane wave and its position isused to select the refraction index for the slab. We introducing a continuous design field and apply The Method of Moving Asymptotes to perform the optimization. A filter...

Analysis of refractive state in 708 children with ametropic amblyopia

Directory of Open Access Journals (Sweden)

Ju-Fen Huang

2016-01-01

Full Text Available AIM: To analyze the refractive state and explore the epidemiologic feature of children with ametropic amblyopia.METHODS: This study retrospectively analyzed 708 children(1 416 eyeswith amblyopia from January 2012 to December 2013 in Special Department of Strabismus and Amblyopic and Department of Pediatric Ophthalmology in our hospital, who were diagnosed as ametropic amblyopia and accepted centrally comprehensive training. The refractive state were given epidemiologic analyze.RESULTS: In the 708 cases(1 416 eyes, there were 190 eyes with hyperopia(13.42%,612 eyes with hyperopia astigmatism(43.22%,18 eyes with myopia(1.27%,134 eyes with myopia astigmatism(9.46%,462 eyes with mixed astigmatism(32.63%. The distributions of refractive state in children at different age were different, and the difference was statistically significant(PCONCLUSION: Hyperopia ametropia and mixed astigmatism are the main types of refractive errors in amblyopia children. The level of amblyopia is related to refractive state and astigmatism axial.

Conceptualization of Light Refraction

Science.gov (United States)

Sokolowski, Andrzej

2013-01-01

There have been a number of papers dealing quantitatively with light refraction. Yet the conceptualization of the phenomenon that sets the foundation for a more rigorous math analysis is minimized. The purpose of this paper is to fill that gap. (Contains 3 figures.)

Parsimonious wave-equation travel-time inversion for refraction waves

KAUST Repository

Fu, Lei; Hanafy, Sherif M.; Schuster, Gerard T.

2017-01-01

We present a parsimonious wave-equation travel-time inversion technique for refraction waves. A dense virtual refraction dataset can be generated from just two reciprocal shot gathers for the sources at the endpoints of the survey line, with N

[Use of Plusoptix as a screening method for refractive ambliopia].

Science.gov (United States)

Bogdănici, T; Tone, Silvia; Miron, Mihaela; Boboc, Mihaela; Bogdănici, Camelia

2012-01-01

Highlighting the differences in the objective refraction using the Plusoptix AO9 comparing them with the refraction performed with TOPCON KR-8900 autorefractor. Prospective study for 3 months held in the Ophthalmology Clinic in Iasi, Hospital Sf. Spiridon on a total of 39 children (21 girls and 18 boys) with mean age of 10.61 +/- 5.67 years. Clinical parameters: sex, age, objective refraction obtained with Plusoptix and with autorefractor corrected visual acuity (with different methods depending on each patient age), ortoptic examination (strabic deviation, binocular vision), the presence of symetry/asymetry while measuring with Plusoptix. The results were statistically processed by F-TEST calculating the correlation coefficient, standard deviation, significance level (using the spherical equivalent of the obtained values). Age limits of the studied cases ranged between 2-23 years. Visual acuity of children who had cooperate was between 0.2-1 with correction, achieving best values on right eye than left eye. 8 cases (20.51%) had large differences between measurements made with Plusoptix and autorefractor, half of that (4 cases) had strabismus. Three of these cases were with small hypermetropia and one with small myopia (Plusoptix shows a lower value). In 2 cases occurred higher differences (about 2-2,5D) between the 2 measurements, in patients with average hypermetropia. Plusoptix refraction was not possible at high hypermetropia or high myopia. This type of determining objective refraction using Plusoptix is a useful method of screening for discovery of refractive errors that can cause refractive amblyopia in young children and in those cases with a difficult collaboration. Because there are differences betweeti this 2 methods, for children with refractive errors are recommended further exploration to determine the appropriate optical correction. Plusoptix is a limited method because it cannot detect the exact values in those cases with high hypermetropia or high

3D super-virtual refraction interferometry

KAUST Repository

Lu, Kai

2014-08-05

Super-virtual refraction interferometry enhances the signal-to-noise ratio of far-offset refractions. However, when applied to 3D cases, traditional 2D SVI suffers because the stationary positions of the source-receiver pairs might be any place along the recording plane, not just along a receiver line. Moreover, the effect of enhancing the SNR can be limited because of the limitations in the number of survey lines, irregular line geometries, and azimuthal range of arrivals. We have developed a 3D SVI method to overcome these problems. By integrating along the source or receiver lines, the cross-correlation or the convolution result of a trace pair with the source or receiver at the stationary position can be calculated without the requirement of knowing the stationary locations. In addition, the amplitudes of the cross-correlation and convolution results are largely strengthened by integration, which is helpful to further enhance the SNR. In this paper, both synthetic and field data examples are presented, demonstrating that the super-virtual refractions generated by our method have accurate traveltimes and much improved SNR.

Fully interferometric controllable anomalous refraction efficiency using cross modulation with plasmonic metasurfaces.

Science.gov (United States)

Liu, Zhaocheng; Chen, Shuqi; Li, Jianxiong; Cheng, Hua; Li, Zhancheng; Liu, Wenwei; Yu, Ping; Xia, Ji; Tian, Jianguo

2014-12-01

We present a method of fully interferometric, controllable anomalous refraction efficiency by introducing cross-modulated incident light based on plasmonic metasurfaces. Theoretical analyses and numerical simulations indicate that the anomalous and ordinary refracted beams generated from two opposite-helicity incident beams and following the generalized Snell's law will have a superposition for certain incident angles, and the anomalous refraction efficiency can be dynamically controlled by changing the relative phase of the incident sources. As the incident wavelength nears the resonant wavelength of the plasmonic metasurfaces, two equal-amplitude incident beams with opposite helicity can be used to control the anomalous refraction efficiency. Otherwise, two unequal-amplitude incident beams with opposite helicity can be used to fully control the anomalous refraction efficiency. This Letter may offer a further step in the development of controllable anomalous refraction.

Optical bulk and surface waves with negative refraction

International Nuclear Information System (INIS)

Agranovich, V.M.; Shen, Y.R.; Baughman, R.H.; Zakhidov, A.A.

2004-01-01

In materials with negative refraction, the direction of wave propagation is opposite to the direction of the wave vector. Using an approach that characterizes the optical response of a medium totally by a generalized dielectric permittivity, ε-bar (ω,k-bar), we discuss the possibility of seeing negative refraction for optical waves in a number of nonmagnetic media. These include bulk waves in organic materials and in gyrotropic materials where additional exciton-polariton waves can have a negative group velocity. It is known that dispersion of surface waves can be engineered by tailoring a surface transition layer. We show how this effect can be used to obtain surface waves with negative refraction

Refractive surgery trends and practice style changes in Germany over a 3-year period.

Science.gov (United States)

Schmack, Ingo; Auffarth, Gerd U; Epstein, Daniel; Holzer, Mike P

2010-03-01

To study the current practice styles and preferences of refractive surgeons in Germany. In February 2008, a seven-item questionnaire regarding the practice of refractive surgery was mailed to 282 members of the German Society of Intra-ocular Lens Implantation, Interventional, and Refractive Surgery (DGII) and the Commission of Refractive Surgery (KRC). Most questions were identical to our 2005 German refractive surgery survey. All data were analyzed in a masked fashion. The response rate was 42.2%. The majority (68%) of respondents reported that they perform refractive surgery in laser centers (exclusively or partially) followed by general hospitals (19.4%) and universities (12.6%). Although LASIK was the predominant type of refractive surgery performed (80.6%), other refractive procedures included refractive lens exchange (60.2%), photorefractive keratectomy (47.6%), phakic intraocular lens implants (45.6%), laser-assisted subepithelial keratectomy (36.9%), epithelial laser in situ keratomileusis (15.5%), intracorneal rings (5.8%), and limbal relaxing incisions (2.9%). The volume of refractive surgery procedures and the preferred type of excimer laser systems, microkeratomes, and diagnostic devices varied at different institutions. Most respondents performed either wavefront-guided custom ablation or wavefront-optimized ablation (63.1%) compared with conventional excimer laser correction (36.9%). Refractive surgery practice styles and preferences in Germany are comparable to trends in other European countries. Although LASIK is the most commonly performed refractive procedure, the numbers of various surface ablation techniques and refractive intraocular lens procedures are increasing. Copyright 2010, SLACK Incorporated.

Surgical Options for the Refractive Correction of Keratoconus: Myth or Reality

Directory of Open Access Journals (Sweden)

L. Fernández-Vega-Cueto

2017-01-01

Full Text Available Keratoconus provides a decrease of quality of life to the patients who suffer from it. The treatment used as well as the method to correct the refractive error of these patients may influence on the impact of the disease on their quality of life. The purpose of this review is to describe the evidence about the conservative surgical treatment for keratoconus aiming to therapeutic and refractive effect. The visual rehabilitation for keratoconic corneas requires addressing three concerns: halting the ectatic process, improving corneal shape, and minimizing the residual refractive error. Cross-linking can halt the disease progression, intrastromal corneal ring segments can improve the corneal shape and hence the visual quality and reduce the refractive error, PRK can correct mild-moderate refractive error, and intraocular lenses can correct from low to high refractive error associated with keratoconus. Any of these surgical options can be performed alone or combined with the other techniques depending on what the case requires. Although it could be considered that the surgical option for the refracto-therapeutic treatment of the keratoconus is a reality, controlled, randomized studies with larger cohorts and longer follow-up periods are needed to determine which refractive procedure and/or sequence are most suitable for each case.

Anterior segment surgery IOLs, lasers, and refractive keratoplasty

Energy Technology Data Exchange (ETDEWEB)

Stark, W.J.; Terry, A.C.; Maumenee, A.E.

1987-01-01

The contributors to this text combine their expertise to make this book available on intraocular lenses, refractive corneal surgery, and the use of the YAG laser. Included is information on; IOL power calculations; the use of the YAG laser; retinal damage by short wavelength light; reviews of corneal refractive surgery; possibilities for the medical prevention of cataracts; and more.

Automated refraction is stable 1 week after uncomplicated cataract surgery

DEFF Research Database (Denmark)

Ostri, Christoffer; Holfort, Stig K; Fich, Marianne S

2018-01-01

PURPOSE: To compare automated refraction 1 week and 1 month after uncomplicated cataract surgery. METHODS: In this prospective cohort study, we recruited patients in a 2-month period and included consecutive patients scheduled for bilateral small-incision phacoemulsification cataract surgery....... The exclusion criteria were (i) corneal and/or retinal pathology that could lead to automated refraction miscalculation and (ii) surgery complications. Automated refraction was measured 1 week and 1 month after surgery. RESULTS: Ninety-five patients met the in- and exclusion criteria and completed follow......-up. The mean refractive shift in spherical equivalent was -0.02 dioptre (D) between 1 week and 1 month after surgery and not statistical significant (p = 0.78, paired t-test). The magnitude of refractive shift in either myopic or hyperopic direction was neither correlated to age, preoperative corneal...

Refraction in Terms of the Deviation of the Light.

Science.gov (United States)

Goldberg, Fred M.

1985-01-01

Discusses refraction in terms of the deviation of light. Points out that in physics courses where very little mathematics is used, it might be more suitable to describe refraction entirely in terms of the deviation, rather than by introducing Snell's law. (DH)

Refractive surgery or contact lenses – how and when to decide?

Directory of Open Access Journals (Sweden)

Xu K

2011-11-01

Full Text Available Kunyong Xu1, Vishal Jhanji2 1Michael G DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada; 2Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong Abstract: Correction of refractive errors can be achieved with spectacles, contact lenses, and refractive surgery. The past decade has seen a surge in the availability of alternatives for patients and surgeons in terms of both surgical and nonsurgical options for the management of refractive errors. Newer generation contact lenses provide enhanced safety and better handling, whereas modern-day refractive surgery presents a plethora of choices based on the clinical characteristics and requirements of patients. We have moved from an era of "one size fits all" to a purely customized way of treating patients with refractive errors. This review presents the background, advantages, and disadvantages of the two most commonly used options for correction of ametropia, ie, contact lenses and refractive surgery. Keywords: laser-assisted in situ keratomileusis, contact lens, patient selection, complications, outcomes

Effect of Cycloplegia on Corneal Biometrics and Refractive State.

Science.gov (United States)

Bagheri, Abbas; Feizi, Mohadeseh; Shafii, Aliakbar; Faramarzi, Amir; Tavakoli, Mehdi; Yazdani, Shahin

2018-01-01

To determine changes in refractive state and corneal parameters after cycloplegia with cyclopentolate hydrochloride 1% using a dual Scheimpflug imaging system. In this prospective cross-sectional study patients aged 10 to 40 years who were referred for optometric evaluation enrolled and underwent autorefraction and corneal imaging with the Galilei dual Scheimpflug system before and 30 minutes after twice instillation of medication. Changes in refraction and astigmatism were investigated. Corneal biometrics including anterior and posterior corneal curvatures, total corneal power and corneal pachymetry were compared before and after cycloplegia. Two hundred and twelve eyes of 106 subjects with mean age of 28 ± 5 years including 201 myopic and 11 hyperopic eyes were evaluated. Mean spherical equivalent refractive error before cycloplegia was -3.4 ± 2.6 D. A mean hyperopic shift of 0.4 ± 0.5 D occurred after cycloplegia ( P biometrics should be considered before cataract and refractive surgeries.

Plasmonic nanoshell functionalized etched fiber Bragg gratings for highly sensitive refractive index measurements.

Science.gov (United States)

Burgmeier, Jörg; Feizpour, Amin; Schade, Wolfgang; Reinhard, Björn M

2015-02-15

A novel fiber optical refractive index sensor based on gold nanoshells immobilized on the surface of an etched single-mode fiber including a Bragg grating is demonstrated. The nanoparticle coating induces refractive index dependent waveguide losses, because of the variation of the evanescently guided part of the light. Hence the amplitude of the Bragg reflection is highly sensitive to refractive index changes of the surrounding medium. The nanoshell functionalized fiber optical refractive index sensor works in reflectance mode, is suitable for chemical and biochemical sensing, and shows an intensity dependency of 4400% per refractive index unit in the refractive index range between 1.333 and 1.346. Furthermore, the physical length of the sensor is smaller than 3 mm with a diameter of 6 μm, and therefore offers the possibility of a localized refractive index measurement.

Refractive and diffractive neutron optics with reduced chromatic aberration

DEFF Research Database (Denmark)

Poulsen, Stefan Othmar; Poulsen, Henning Friis; Bentley, P.M.

2014-01-01

by the use of optics for focusing and imaging. Refractive and diffractive optical elements, e.g. compound refractive lenses and Fresnel zone plates, are attractive due to their low cost, and simple alignment. These optical elements, however, suffer from chromatic aberration, which limit their effectiveness...

Technique for forming ITO films with a controlled refractive index

Energy Technology Data Exchange (ETDEWEB)

Markov, L. K., E-mail: l.markov@mail.ioffe.ru; Smirnova, I. P.; Pavluchenko, A. S.; Kukushkin, M. V.; Zakheim, D. A.; Pavlov, S. I. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation)

2016-07-15

A new method for fabricating transparent conducting coatings based on indium-tin oxide (ITO) with a controlled refractive index is proposed. This method implies the successive deposition of material by electron-beam evaporation and magnetron sputtering. Sputtered coatings with different densities (and, correspondingly, different refractive indices) can be obtained by varying the ratio of the mass fractions of material deposited by different methods. As an example, films with effective refractive indices of 1.2, 1.4, and 1.7 in the wavelength range of 440–460 nm are fabricated. Two-layer ITO coatings with controlled refractive indices of the layers are also formed by the proposed method. Thus, multilayer transparent conducting coatings with desired optical parameters can be produced.

Refractive index based measurements

DEFF Research Database (Denmark)

2014-01-01

In a method for performing a refractive index based measurement of a property of a fluid such as chemical composition or temperature, a chirp in the local spatial frequency of interference fringes of an interference pattern is reduced by mathematical manipulation of the recorded light intensity...

On the anodic aluminium oxide refractive index of nanoporous templates

International Nuclear Information System (INIS)

Hierro-Rodriguez, A; Rocha-Rodrigues, P; Araujo, J P; Valdés-Bango, F; Alameda, J M; Teixeira, J M; Jorge, P A S; Santos, J L; Guerreiro, A

2015-01-01

In the present study, we have determined the intrinsic refractive index of anodic aluminium oxide, which is originated by the formation of nanoporous alumina templates. Different templates have been fabricated by the conventional two-step anodization procedure in oxalic acid. Their porosities were modified by chemical wet etching allowing the tuning of their effective refractive indexes (air-filled nanopores  +  anodic aluminium oxide). By standard spectroscopic light transmission measurements, the effective refractive index for each different template was extracted in the VIS–NIR region. The determination of the intrinsic anodic aluminium oxide refractive index was performed by using the Maxwell–Garnett homogenization theory. The results are coincident for all the fabricated samples. The obtained refractive index (∼1.55) is quite lower (∼22%) than the commonly used Al 2 O 3 handbook value (∼1.75), showing that the amorphous nature of the anodic oxide structure strongly conditions its optical properties. This difference is critical for the correct design and modeling of optical plasmonic metamaterials based on anodic aluminium oxide nanoporous templates. (paper)

Refractive errors among children, adolescents and adults attending eye clinics in Mexico

Directory of Open Access Journals (Sweden)

Francisco Gomez-Salazar

2017-05-01

Full Text Available AIM: To assess the proportion of refractive errors in the Mexican population that visited primary care optometry clinics in fourteen states of Mexico. METHODS: Refractive data from 676 856 patients aged 6 to 90y were collected from optometry clinics in fourteen states of Mexico between 2014 and 2015. The refractive errors were classified by the spherical equivalent (SE, as follows: sphere+½ cylinder. Myopia (SE>-0.50 D, hyperopia (SE>+0.50 D, emmetropia (-0.50≤SE≤+0.50, and astigmatism alone (cylinder≥-0.25 D. A negative cylinder was selected as a notation. RESULTS: The proportion (95% confidence interval among all of the subjects was hyperopia 21.0% (20.9-21.0, emmetropia 40.7% (40.5-40.8, myopia 24.8% (24.7-24.9 and astigmatism alone 13.5% (13.4-13.5. Myopia was the most common refractive error and frequency seemed to increase among the young population (10 to 29 years old, however, hyperopia increased among the aging population (40 to 79 years old, and astigmatism alone showed a decreasing trend with age (6 to 90y; from 19.7% to 10.8%. There was a relationship between age and all refractive errors (approximately 60%, aged 50 and older. The proportion of any clinically important refractive error was higher in males (61.2% than in females (58.3%; P<0.0001. From fourteen states that collected information, the proportion of refractive error showed variability in different geographical areas of Mexico. CONCLUSION: Myopia is the most common refractive error in the population studied. This study provides the first data on refractive error in Mexico. Further programs and studies must be developed to address the refractive errors needs of the Mexican population.

Generalized laws of reflection and refraction from transformation optics

OpenAIRE

Xu, Yadong; Yao, Kan; Chen, Huanyang

2012-01-01

Based on transformation optics, we introduce another set of generalized laws of reflection and refraction (differs from that of [Science 334, 333 (2011)]), through which a transformation media slab is derived as a meta-surface, producing anomalous reflection and refraction for all polarizations of incident light.

Nano-imprint gold grating as refractive index sensor

International Nuclear Information System (INIS)

Kumari, Sudha; Mohapatra, Saswat; Moirangthem, Rakesh S.

2016-01-01

Large scale of fabrication of plasmonic nanostructures has been a challenging task due to time consuming process and requirement of expensive nanofabrication tools such as electron beam lithography system, focused ion beam system, and extreme UV photolithography system. Here, we present a cost-effective fabrication technique so called soft nanoimprinting to fabricate nanostructures on the larger sample area. In our fabrication process, a commercially available optical DVD disc was used as a template which was imprinted on a polymer glass substrate to prepare 1D polymer nano-grating. A homemade nanoimprinting setup was used in this fabrication process. Further, a label-free refractive index sensor was developed by utilizing the properties of surface plasmon resonance (SPR) of a gold coated 1D polymer nano-grating. Refractive index sensing was tested by exposing different solutions of glycerol-water mixture on the surface of gold nano-grating. The calculated bulk refractive index sensitivity was found to be 751nm/RIU. We believed that our proposed SPR sensor could be a promising candidate for developing low-cost refractive index sensor with high sensitivity on a large scale.

Refractive state of the Spanish Thoroughbred horse: a comparison with the Crossbred horse.

Science.gov (United States)

Rull-Cotrina, Jorge; Molleda, Jose M; Gallardo, José; Martín-Suárez, Eva

2013-01-01

To assess the refractive state of the equine eye utilizing retinoscopy. To compare the refractive state of Spanish Thoroughbred horses with the refractive state of Crossbred horses. The refractive state of 135 horses (264 eyes) was assessed utilizing streak retinoscopy. Two perpendicular meridians were examined in order to assess astigmatism at a working distance of approximately 67 cm. A group of 81 Spanish Thoroughbred horses was compared with a group of 54 Crossbred horses. Cyclopentolate ophthalmic solution was instilled in the eyes of a group of 18 horses to determine if accommodation has any influence on the assessment of the refractive state.   Mean ± SE refractive state of all horses examined was -0.17 ± 0.04 D. The mean refractive state of the Spanish Thoroughbred was -0.28 ± 0.06 D while that of the Crossbred was -0.01 ± 0.05 D. The refractive state of the Spanish Thoroughbred was found to be statistically different to that of the Crossbred. The most prevalent refractive state was emmetropia in all cases, followed by hyperopia for the Crossbred, and myopia for the Spanish Thoroughbred. Astigmatism ≥0.50 D present in both eyes from the same individual was found in 21.7% of all horses examined. Anisometropia ≥1.00 D was diagnosed in 4 out of 129 horses with both visual eyes. Cycloplegia did not statistically affect the refractive state of the evaluated eyes. The equine eye has a refractive state close to emmetropia. Myopia is higher among Spanish Thoroughbred horses than among Crossbred horses. © 2012 American College of Veterinary Ophthalmologists.

Experimental and predicted refractive index properties in ternary mixtures of associated liquids

International Nuclear Information System (INIS)

Sechenyh, Vitaliy V.; Legros, Jean-Claude; Shevtsova, Valentina

2011-01-01

Highlights: → Measurements of refractive indices of 200 different aqueous ternary mixtures have been performed for two wave lengths. → Refractive indices of the associated ternary mixtures can be modeled with a relative error of about 0.9. → Difference between experimental and calculated derivatives of refractive index with concentration is unsatisfactory large. - Abstract: Refractive indices of ternary mixtures formed by (water + ethanol + k-ethylene glycol) (when k is mono, di or tri) and (water + t-butanol + dimethyl sulfoxide) are presented over a wide range of mixture compositions. All measurements have been conducted at 298.15 K and atmospheric pressure using two light sources: one in the visible (λ = 670 nm) and the other in the infrared (λ = 925 nm) spectrum. The performance of several mixing rules that are commonly used in modeling optical constants are examined. We demonstrate that the refractive indices of the associated ternary mixtures can be modeled with a relative error of about 0.9% by using the thermodynamical properties of the pure components. The concentration derivatives of the refractive index are an important parameter, as they are required for different experimental techniques. These derivatives have been determined from the experimental data on refractive indices. However, applying mixing rules for calculation of the derivatives of the refractive indices with respect to concentrations does not provide satisfactory results in the case of ternary mixtures of associated liquids.

Empirical temperature dependence of the refractive index of semiconductors

NARCIS (Netherlands)

Herve, P.J.L.; Vandamme, L.K.J.

1995-01-01

Values of the temperature coefficient of the refractive index were obtained from the derivation of a simple relation between energy band-gap and refractive index in semiconductors. These values, (dn/dT)/n, were compared to the experimental data found in literature. Our model, with only one fitting

Prevalence of Refractive Error and Visual Impairment among Rural ...

African Journals Online (AJOL)

GB

prevalence of refractive error was 3.5% (myopia 2.6% and hyperopia 0.9%). Refractive error ... 2Department of Ophthalmology, Addis Ababa University Medical Faculty, Ethiopia. Corresponding ... the main cause of low vision and the second cause of blindness .... the visual loss. All data were entered into computers using.

Refractive aim and visual outcome after phacoemulsification: A 2 ...

African Journals Online (AJOL)

2016-03-24

Mar 24, 2016 ... was met, 21 eyes (14.3%) did not meet their refractive aim, 20 eyes (12.7%) were ... countries, where blindness is associated with considerable ... and better, the total range of refractive errors postoperatively ... required intraocular lenses (IOL), medical record efficiency, ..... problem that can be alleviated.

A comparison of cycloplegic autorefraction and retinoscopy in Indian children.

Science.gov (United States)

Guha, Sujata; Shah, Sanil; Shah, Khyati; Hurakadli, Preeti; Majee, Debalina; Gandhi, Shyamali

2017-01-01

Correction of significant refractive errors in childhood helps in preventing amblyopia and strabismus. India has a huge demand for eye-care services related to uncorrected refractive errors with limited manpower resources. This can be overcome by autorefractors, which are free of operator bias, do not need skilled eye-care professionals and can be operated with ease. Hence, the purpose of this study, the first in the Indian population, was to determine the accuracy of autorefraction compared to traditional retinoscopy under cycloplegia. A cross-sectional study of all children meeting our inclusion criteria was conducted from July till October 2011 in a tertiary eye care centre. Children underwent cycloplegic (cyclopentolate plus tropicamide) refraction with an auto-refractometer (Topcon KR-8900) and traditional retinoscopy and the results were compared. Patients were divided into three groups: Group 1: Myopia and myopic astigmatism, Group 2: Hyperopia and hyperopic astigmatism and Group 3: Mixed astigmatism. Clinically significant difference was defined as either of more than 0.50 D difference in sphere, more than 0.5 D difference in cylinder or more than 20 degrees difference in axis. The left eyes of 294 children (148 male) were included in the study. Mean age was 8.22 ± 3.47 years. Clinically significant differences were noted in 13.22 per cent of eyes in Group 1, 15.09 per cent of eyes in Group 2 and 20.90 per cent of eyes in Group 3. Clinically significant differences were more common in children aged less than six years (25 per cent) compared to older children (9.19 per cent). Comparing the sphere, cylinder, spherical equivalent and length of power vector values gained by autorefraction and retinoscopy, no statistically significant differences were found in any group. Autorefraction with Topcon KR-8900 can be used reliably in Indian children older than six years, if conducted under cycloplegia. In mixed astigmatism and children less than six years, it should

Refractive-index changes in lithium niobate crystals by radiation damages

International Nuclear Information System (INIS)

Zamani Meymian, Mohammad Reza

2007-01-01

For the study in this thesis 3 He 2+ ions with the energy of about 40 MeV were applied. The results of these studies show a timely very stable anisotrope refractive-index change in the range of some 10 -3 . The radiation damages caused by ions cause a decreasement of the ordinary refractive index n o and an increasement of the extra-ordinary refractive index n e . While the absolute values for Δn o and Δn e are nearly equal the birefringence of the material (n e -n o ) smaller. The generated refractive-index change is dose dependent and the curve Δn has at increasing dose a strongly nonlinear slope with a characteristic stage at the radiation dose of about 2 x 10 20 ions/m 2

Measurement of the Microwave Refractive Index of Materials Based on Parallel Plate Waveguides

Science.gov (United States)

Zhao, F.; Pei, J.; Kan, J. S.; Zhao, Q.

2017-12-01

An electrical field scanning apparatus based on a parallel plate waveguide method is constructed, which collects the amplitude and phase matrices as a function of the relative position. On the basis of such data, a method for calculating the refractive index of the measured wedge samples is proposed in this paper. The measurement and calculation results of different PTFE samples reveal that the refractive index measured by the apparatus is substantially consistent with the refractive index inferred with the permittivity of the sample. The proposed refractive index calculation method proposed in this paper is a competitive method for the characterization of the refractive index of materials with positive refractive index. Since the apparatus and method can be used to measure and calculate arbitrary direction of the microwave propagation, it is believed that both of them can be applied to the negative refractive index materials, such as metamaterials or “left-handed” materials.

Refraction-compensated motion tracking of unrestrained small animals in positron emission tomography.

Science.gov (United States)

Kyme, Andre; Meikle, Steven; Baldock, Clive; Fulton, Roger

2012-08-01

Motion-compensated radiotracer imaging of fully conscious rodents represents an important paradigm shift for preclinical investigations. In such studies, if motion tracking is performed through a transparent enclosure containing the awake animal, light refraction at the interface will introduce errors in stereo pose estimation. We have performed a thorough investigation of how this impacts the accuracy of pose estimates and the resulting motion correction, and developed an efficient method to predict and correct for refraction-based error. The refraction model underlying this study was validated using a state-of-the-art motion tracking system. Refraction-based error was shown to be dependent on tracking marker size, working distance, and interface thickness and tilt. Correcting for refraction error improved the spatial resolution and quantitative accuracy of motion-corrected positron emission tomography images. Since the methods are general, they may also be useful in other contexts where data are corrupted by refraction effects. Crown Copyright © 2012. Published by Elsevier B.V. All rights reserved.

Prevalence of Refractive Error and Visual Impairment among Rural ...

African Journals Online (AJOL)

Refractive error was the major cause of visual impairment accounting for 54% of all causes in the study group. No child was found wearing ... So, large scale community level screening for refractive error should be conducted and integrated with regular school eye screening programs. Effective strategies need to be devised ...

Trial frame refraction versus autorefraction among new patients in a low-vision clinic.

Science.gov (United States)

DeCarlo, Dawn K; McGwin, Gerald; Searcey, Karen; Gao, Liyan; Snow, Marsha; Waterbor, John; Owsley, Cynthia

2013-01-02

To determine the relationship between refractive error as measured by autorefraction and that measured by trial frame refraction among a sample of adults with vision impairment seen in a university-based low-vision clinic and to determine if autorefraction might be a suitable replacement for trial frame refraction. A retrospective chart review of all new patients 19 years or older seen over an 18-month period was conducted and the following data collected: age, sex, primary ocular diagnosis, entering distance visual acuity, habitual correction, trial frame refraction, autorefraction, and distance visual acuity measured after trial frame refraction. Trial frame refraction and autorefraction were compared using paired t-tests, intraclass correlations, and Bland-Altman plots. Final analyses included 440 patients for whom both trial frame refraction and autorefraction data were available for the better eye. Participants were mostly female (59%) with a mean age of 68 years (SD = 20). Age-related macular degeneration was the most common etiology for vision impairment (44%). Values for autorefraction and trial frame refraction were statistically different, but highly correlated for the spherical equivalent power (r = 0.92), the cylinder power (r = 0.80) and overall blurring strength (0.89). Although the values of the cross-cylinders J(0) and J(45) were similar, they were poorly correlated (0.08 and 0.15, respectively). The range of differences in spherical equivalent power was large (-8.6 to 4.9). Autorefraction is highly correlated with trial frame refraction. Differences are sometimes substantial, making autorefraction an unsuitable substitute for trial frame refraction.

Is LASIK for Me? A Patient's Guide to Refractive Surgery

Science.gov (United States)

Is LASIK for Me? A Patient’s Guide to Refractive Surgery October 2008 Is LASIK for Me? A Patient’s Guide to Refractive Surgery Table of Contents LASIK: A COMPREHENSIVE GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 What Is ...

Refractive errors in children and adolescents in Bucaramanga (Colombia).

Science.gov (United States)

Galvis, Virgilio; Tello, Alejandro; Otero, Johanna; Serrano, Andrés A; Gómez, Luz María; Castellanos, Yuly

2017-01-01

The aim of this study was to establish the frequency of refractive errors in children and adolescents aged between 8 and 17 years old, living in the metropolitan area of Bucaramanga (Colombia). This study was a secondary analysis of two descriptive cross-sectional studies that applied sociodemographic surveys and assessed visual acuity and refraction. Ametropias were classified as myopic errors, hyperopic errors, and mixed astigmatism. Eyes were considered emmetropic if none of these classifications were made. The data were collated using free software and analyzed with STATA/IC 11.2. One thousand two hundred twenty-eight individuals were included in this study. Girls showed a higher rate of ametropia than boys. Hyperopic refractive errors were present in 23.1% of the subjects, and myopic errors in 11.2%. Only 0.2% of the eyes had high myopia (≤-6.00 D). Mixed astigmatism and anisometropia were uncommon, and myopia frequency increased with age. There were statistically significant steeper keratometric readings in myopic compared to hyperopic eyes. The frequency of refractive errors that we found of 36.7% is moderate compared to the global data. The rates and parameters statistically differed by sex and age groups. Our findings are useful for establishing refractive error rate benchmarks in low-middle-income countries and as a baseline for following their variation by sociodemographic factors.

Refractive errors in children and adolescents in Bucaramanga (Colombia

Directory of Open Access Journals (Sweden)

Virgilio Galvis

Full Text Available ABSTRACT Purpose: The aim of this study was to establish the frequency of refractive errors in children and adolescents aged between 8 and 17 years old, living in the metropolitan area of Bucaramanga (Colombia. Methods: This study was a secondary analysis of two descriptive cross-sectional studies that applied sociodemographic surveys and assessed visual acuity and refraction. Ametropias were classified as myopic errors, hyperopic errors, and mixed astigmatism. Eyes were considered emmetropic if none of these classifications were made. The data were collated using free software and analyzed with STATA/IC 11.2. Results: One thousand two hundred twenty-eight individuals were included in this study. Girls showed a higher rate of ametropia than boys. Hyperopic refractive errors were present in 23.1% of the subjects, and myopic errors in 11.2%. Only 0.2% of the eyes had high myopia (≤-6.00 D. Mixed astigmatism and anisometropia were uncommon, and myopia frequency increased with age. There were statistically significant steeper keratometric readings in myopic compared to hyperopic eyes. Conclusions: The frequency of refractive errors that we found of 36.7% is moderate compared to the global data. The rates and parameters statistically differed by sex and age groups. Our findings are useful for establishing refractive error rate benchmarks in low-middle-income countries and as a baseline for following their variation by sociodemographic factors.

Imaging of Subsurface Faults using Refraction Migration with Fault Flooding

KAUST Repository

Metwally, Ahmed Mohsen Hassan

2017-05-31

We propose a novel method for imaging shallow faults by migration of transmitted refraction arrivals. The assumption is that there is a significant velocity contrast across the fault boundary that is underlain by a refracting interface. This procedure, denoted as refraction migration with fault flooding, largely overcomes the difficulty in imaging shallow faults with seismic surveys. Numerical results successfully validate this method on three synthetic examples and two field-data sets. The first field-data set is next to the Gulf of Aqaba and the second example is from a seismic profile recorded in Arizona. The faults detected by refraction migration in the Gulf of Aqaba data were in agreement with those indicated in a P-velocity tomogram. However, a new fault is detected at the end of the migration image that is not clearly seen in the traveltime tomogram. This result is similar to that for the Arizona data where the refraction image showed faults consistent with those seen in the P-velocity tomogram, except it also detected an antithetic fault at the end of the line. This fault cannot be clearly seen in the traveltime tomogram due to the limited ray coverage.

Refractive index dependence of Papilio Ulysses butterfly wings reflectance spectra

Science.gov (United States)

Isnaeni, Muslimin, Ahmad Novi; Birowosuto, Muhammad Danang

2016-02-01

We have observed and utilized butterfly wings of Papilio Ulysses for refractive index sensor. We noticed this butterfly wings have photonic crystal structure, which causes blue color appearance on the wings. The photonic crystal structure, which consists of cuticle and air void, is approximated as one dimensional photonic crystal structure. This photonic crystal structure opens potential to several optical devices application, such as refractive index sensor. We have utilized small piece of Papilio Ulysses butterfly wings to characterize refractive index of several liquid base on reflectance spectrum of butterfly wings in the presence of sample liquid. For comparison, we simulated reflectance spectrum of one dimensional photonic crystal structure having material parameter based on real structure of butterfly wings. We found that reflectance spectrum peaks shifted as refractive index of sample changes. Although there is a slight difference in reflectance spectrum peaks between measured spectrum and calculated spectrum, the trend of reflectance spectrum peaks as function of sample's refractive index is the similar. We assume that during the measurement, the air void that filled by sample liquid is expanded due to liquid pressure. This change of void shape causes non-similarity between measured spectrum and calculated spectrum.

Imaging of Subsurface Faults using Refraction Migration with Fault Flooding

KAUST Repository

Metwally, Ahmed Mohsen Hassan; Hanafy, Sherif; Guo, Bowen; Kosmicki, Maximillian Sunflower

2017-01-01

We propose a novel method for imaging shallow faults by migration of transmitted refraction arrivals. The assumption is that there is a significant velocity contrast across the fault boundary that is underlain by a refracting interface. This procedure, denoted as refraction migration with fault flooding, largely overcomes the difficulty in imaging shallow faults with seismic surveys. Numerical results successfully validate this method on three synthetic examples and two field-data sets. The first field-data set is next to the Gulf of Aqaba and the second example is from a seismic profile recorded in Arizona. The faults detected by refraction migration in the Gulf of Aqaba data were in agreement with those indicated in a P-velocity tomogram. However, a new fault is detected at the end of the migration image that is not clearly seen in the traveltime tomogram. This result is similar to that for the Arizona data where the refraction image showed faults consistent with those seen in the P-velocity tomogram, except it also detected an antithetic fault at the end of the line. This fault cannot be clearly seen in the traveltime tomogram due to the limited ray coverage.

Empirical modelling to predict the refractive index of human blood

Science.gov (United States)

Yahya, M.; Saghir, M. Z.

2016-02-01

Optical techniques used for the measurement of the optical properties of blood are of great interest in clinical diagnostics. Blood analysis is a routine procedure used in medical diagnostics to confirm a patient’s condition. Measuring the optical properties of blood is difficult due to the non-homogenous nature of the blood itself. In addition, there is a lot of variation in the refractive indices reported in the literature. These are the reasons that motivated the researchers to develop a mathematical model that can be used to predict the refractive index of human blood as a function of concentration, temperature and wavelength. The experimental measurements were conducted on mimicking phantom hemoglobin samples using the Abbemat Refractometer. The results analysis revealed a linear relationship between the refractive index and concentration as well as temperature, and a non-linear relationship between refractive index and wavelength. These results are in agreement with those found in the literature. In addition, a new formula was developed based on empirical modelling which suggests that temperature and wavelength coefficients be added to the Barer formula. The verification of this correlation confirmed its ability to determine refractive index and/or blood hematocrit values with appropriate clinical accuracy.

Longitudinal change and stability of refractive, keratometric, and internal astigmatism in childhood.

Science.gov (United States)

Harvey, Erin M; Miller, Joseph M; Twelker, J Daniel; Sherrill, Duane L

2014-12-16

To assess longitudinal change in refractive, keratometric, and internal astigmatism in a sample of students from a population with a high prevalence of with-the-rule (WTR) astigmatism and to determine the optical origins of changes in refractive astigmatism. A retrospective analysis of longitudinal measurements of right eye refractive and keratometric astigmatism in Tohono O'odham Native American children was conducted. Changes in refractive and keratometric astigmatism per year were compared in a younger cohort (n = 1594, 3 to O'odham children. Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc.

Polymer X-ray refractive nano-lenses fabricated by additive technology.

Science.gov (United States)

Petrov, A K; Bessonov, V O; Abrashitova, K A; Kokareva, N G; Safronov, K R; Barannikov, A A; Ershov, P A; Klimova, N B; Lyatun, I I; Yunkin, V A; Polikarpov, M; Snigireva, I; Fedyanin, A A; Snigirev, A

2017-06-26

The present work demonstrates the potential applicability of additive manufacturing to X-Ray refractive nano-lenses. A compound refractive lens with a radius of 5 µm was produced by the two-photon polymerization induced lithography. It was successfully tested at the X-ray microfocus laboratory source and a focal spot of 5 μm was measured. An amorphous nature of polymer material combined with the potential of additive technologies may result in a significantly enhanced focusing performance compared to the best examples of modern X-ray compound refractive lenses.

An optomechanical model eye for ophthalmological refractive studies.

Science.gov (United States)

Arianpour, Ashkan; Tremblay, Eric J; Stamenov, Igor; Ford, Joseph E; Schanzlin, David J; Lo, Yuhwa

2013-02-01

To create an accurate, low-cost optomechanical model eye for investigation of refractive errors in clinical and basic research studies. An optomechanical fluid-filled eye model with dimensions consistent with the human eye was designed and fabricated. Optical simulations were performed on the optomechanical eye model, and the quantified resolution and refractive errors were compared with the widely used Navarro eye model using the ray-tracing software ZEMAX (Radiant Zemax, Redmond, WA). The resolution of the physical optomechanical eye model was then quantified with a complementary metal-oxide semiconductor imager using the image resolution software SFR Plus (Imatest, Boulder, CO). Refractive, manufacturing, and assembling errors were also assessed. A refractive intraocular lens (IOL) and a diffractive IOL were added to the optomechanical eye model for tests and analyses of a 1951 U.S. Air Force target chart. Resolution and aberrations of the optomechanical eye model and the Navarro eye model were qualitatively similar in ZEMAX simulations. Experimental testing found that the optomechanical eye model reproduced properties pertinent to human eyes, including resolution better than 20/20 visual acuity and a decrease in resolution as the field of view increased in size. The IOLs were also integrated into the optomechanical eye model to image objects at distances of 15, 10, and 3 feet, and they indicated a resolution of 22.8 cycles per degree at 15 feet. A life-sized optomechanical eye model with the flexibility to be patient-specific was designed and constructed. The model had the resolution of a healthy human eye and recreated normal refractive errors. This model may be useful in the evaluation of IOLs for cataract surgery. Copyright 2013, SLACK Incorporated.

Automatic diagnostic system for measuring ocular refractive errors

Science.gov (United States)

Ventura, Liliane; Chiaradia, Caio; de Sousa, Sidney J. F.; de Castro, Jarbas C.

1996-05-01

Ocular refractive errors (myopia, hyperopia and astigmatism) are automatic and objectively determined by projecting a light target onto the retina using an infra-red (850 nm) diode laser. The light vergence which emerges from the eye (light scattered from the retina) is evaluated in order to determine the corresponding ametropia. The system basically consists of projecting a target (ring) onto the retina and analyzing the scattered light with a CCD camera. The light scattered by the eye is divided into six portions (3 meridians) by using a mask and a set of six prisms. The distance between the two images provided by each of the meridians, leads to the refractive error of the referred meridian. Hence, it is possible to determine the refractive error at three different meridians, which gives the exact solution for the eye's refractive error (spherical and cylindrical components and the axis of the astigmatism). The computational basis used for the image analysis is a heuristic search, which provides satisfactory calculation times for our purposes. The peculiar shape of the target, a ring, provides a wider range of measurement and also saves parts of the retina from unnecessary laser irradiation. Measurements were done in artificial and in vivo eyes (using cicloplegics) and the results were in good agreement with the retinoscopic measurements.

Wave Refraction During the May 2002 Rarefaction Event

Science.gov (United States)

Smith, C. W.; Mullan, D. J.; Ness, N. F.; Skoug, R. M.

2002-12-01

In previous work [Smith et al., 2001] we examined IMF wave refraction during the May 1999 rarefaction interval known as ``The Day The Solar Wind Disappeared.'' On that day, Alfvén speeds remained elevated over an extended region. Analysis of the recorded ACE fields and plasma data revealed depressed magnetic fluctuation levels, reduced compression in the fluctuations, and a reduced wave-like component within the region of elevated Alfvén speed, all consistent with wave refraction. The May 2002 event provides a third such period (the second identified event occured 2 weeks prior to the May 1999 period) and it again demonstrates properties which are consistent with refraction. Smith, C.~W., D.~J. Mullan, N.~F. Ness, R.~M. Skoug, and J.~Steinberg, Day the solar wind almost disappeared: Magnetic field fluctuations, wave refraction and dissipation, J. Geophys. Res., A106, 18,625--18,634, 2001. Efforts at the Bartol Research Institute were supported by CIT subcontract PC251439 under NASA grant NAG5-6912 for support of the ACE magnetic field experiment and by the NASA Delaware Space College Grant. Work at Los Alamos was performed under the auspices of the U.S. Department of Energy with financial support from the NASA ACE program.

Refractive index retrieving of polarization maintaining optical fibers

Science.gov (United States)

Ramadan, W. A.; Wahba, H. H.; Shams El-Din, M. A.; Abd El-Sadek, I. G.

2018-01-01

In this paper, the cross-section images, of two different types of polarization maintaining (PM) optical fibers, are employed to estimate the optical phase variation due to transverse optical rays passing through these optical fibers. An adaptive algorithm is proposed to recognize the different areas constituting the PM optical fibers cross-sections. These areas are scanned by a transverse beam to calculate the optical paths for given values of refractive indices. Consequently, the optical phases across the PM optical fibers could be recovered. PM optical fiber is immersed in a matching fluid and set in the object arm of Mach-Zehnder interferometer. The produced interferograms are analyzed to extract the optical phases caused by the PM optical fibers. The estimated optical phases could be optimized to be in good coincidence with experimentally extracted ones. This has been achieved through changing of the PM optical fibers refractive indices to retrieve the correct values. The correct refractive indices values are confirmed by getting the best fit between the estimated and the extracted optical phases. The presented approach is a promising one because it provides a quite direct and accurate information about refractive index, birefringence and beat length of PM optical fibers comparing with different techniques handle the same task.

Microfocussing of synchrotron X-rays using X-ray refractive lens ...

Indian Academy of Sciences (India)

2014-07-02

Jul 2, 2014 ... together. The first refractive lenses for hard X-rays were fabricated and tested by Snigirev et al [3]. ... using silicon and diamond refractive lens materials [4]. Many groups ... PMMA has lower radiation resistance com- pared to ...

Refractive and diffractive neutron optics with reduced chromatic aberration

Energy Technology Data Exchange (ETDEWEB)

Poulsen, S.O., E-mail: stefan.poulsen@northwestern.edu [NEXMAP, Department of Physics, Technical University of Denmark, Anker Engelunds Vej 1, 2800 Kgs. Lyngby (Denmark); Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208 (United States); Poulsen, H.F. [NEXMAP, Department of Physics, Technical University of Denmark, Anker Engelunds Vej 1, 2800 Kgs. Lyngby (Denmark); Bentley, P.M. [European Spallation Source ESS AB, Box 176, 221 00 Lund (Sweden)

2014-12-11

Thermal neutron beams are an indispensable tool in physics research. The spatial and the temporal resolution attainable in experiments are dependent on the flux and collimation of the neutron beam which remain relatively poor, even for modern neutron sources. These difficulties may be mitigated by the use of optics for focusing and imaging. Refractive and diffractive optical elements, e.g. compound refractive lenses and Fresnel zone plates, are attractive due to their low cost, and simple alignment. These optical elements, however, suffer from chromatic aberration, which limit their effectiveness to highly monochromatic beams. This paper presents two novel concepts for focusing and imaging non-monochromatic thermal neutron beams with well-known optical elements: (1) a fast mechanical transfocator based on a compound refractive lens, which actively varies the number of individual lenses in the beam path to focus and image a time-of-flight beam, and (2) a passive optical element consisting of a compound refractive lens, and a Fresnel zone plate, which may focus and image both continuous and pulsed neutron beams.

Refractive Index Sensor Using a Two-Hole Fiber

Energy Technology Data Exchange (ETDEWEB)

Lopez-Cortes, D; Sanchez-Mondragon, J J [Photonics and Optical Physics Laboratory, Optics Department, INAOE Apdo. Postal 51 and 216, Tonantzintla, Puebla 72000 (Mexico); Margulis, W [Department Fiber Photonics, ACREO, Electrum 236, 16440 Stockholm (Sweden); Dominguez-Cruz, R; May-Arrioja, D A, E-mail: darrioja@uat.edu.mx [Depto. de Ingenieria Electronica, UAM Reynosa Rodhe, Universidad Autonoma de Tamaulipas, Carr. Reynosa-San Fernando S/N, Reynosa, Tamaulipas 88779 (Mexico)

2011-01-01

We propose to use a twin-hole fiber to measure refractive index of liquids. The key idea is to have a single mode fiber (SMF) having two large air-holes running along the fiber length, the holes do not interact with the core. However, using wet chemical etching we can have access to the hole around the fiber, and further etching increases the holes diameter. The diameter is increased until the fiber exhibits a specific birefringence. Since the holes are open, by immersing the fiber in different liquids (n=1.33 to n=1.42) the value of the birefringence is modified and the refractive index of the liquid can be estimated from the change on the beat length. This process provides a very simple and highly sensitive mechanism for sensing refractive index in liquids, and can also be used for other applications.

[Correction of light refraction and reflection in medical transmission optical tomography].

Science.gov (United States)

Tereshchenko, S A; Potapov, D A

2002-01-01

The effects of light refraction and reflection on the quality of image reconstruction in medical transmission optical tomography of high-scattering media are considered. It has been first noted that light refraction not only distorts the geometric scheme of measurements, but may lead to the appearance of object areas that cannot be scanned. Some ways of decreasing the effect of refraction on the reconstruction of spatial distribution of the extinction coefficient are stated.

1D Photonic Crystals with a Sawtooth Refractive Index

OpenAIRE

Morozov, G. V.; Sprung, D. W. L.; Martorell, J.

2013-01-01

Exact analytical results (in terms of Bessel functions) for the bandgaps, reflectance, and transmittance of one-dimensional photonic crystals with a sawtooth refractive index profile on the period are derived for the first time. This extends a group of exactly solvable models of periodic refractive indices. The asymptotic approximations of the above exact results have been also obtained.

Index of Refraction Measurements Using a Laser Distance Meter

Science.gov (United States)

Ochoa, Romulo; Fiorillo, Richard; Ochoa, Cris

2014-01-01

We present a simple method to determine the refractive indices of transparent media using a laser distance meter. Indices of refraction have been obtained by measuring the speed of light in materials. Some speed of light techniques use time-of-flight measurements in which pulses are emitted by lasers and the time interval is measured for the pulse…

A Model of the Effect of Lens Development on Refraction in Schoolchildren.

Science.gov (United States)

He, Ji C

2017-12-01

The study provides a new theory on the mechanism underlying myopia development, and it could be useful in clinical practice to control myopia development in schoolchildren. To model the effect of the crystalline lens on refractive development in schoolchildren. The Zemax 13 was used to calculate Zernike aberrations and refractions across 50° horizontal visual fields. Optical effects of the anterior chamber depth, lens thickness, and radii of curvature of the lens surfaces on refractions were modeled. Refractive changes induced by lens development in emmetropic and myopic eyes, based on a previous longitudinal study from literature, were calculated. A lens thickness reduction with an anterior chamber depth deepening caused a hyperopic shift over the visual fields and even more at the periphery. Opposite effects were found when the lens was thinned without any change of the anterior chamber depth. While a flattening of the anterior lens surface produced hyperopic refractions overall, a posterior lens flattening caused a myopic shift at the periphery, but a hyperopic shift of the central refraction. In the myopic eye, lens development induced refractive change toward more hyperopic over the visual fields and more at the periphery. Lens thinning and lens axial movement participate in peripheral refractive development in schoolchildren, and lens development with a deeper anterior chamber depth and a flatter lens surface in the myopic eye could generate extra hyperopia over visual fields. The myopic lens development could be due to a backward movement of the lens, driven by a backward growth of the ciliary process, which might be a causative factor of myopia development.

Calculation and simulation of atmospheric refraction effects in maritime environments

Science.gov (United States)

Dion, Denis, Jr.; Gardenal, Lionel; Lahaie, P.; Forand, J. Luc

2001-01-01

Near the sea surface, atmospheric refraction and turbulence affect both IR transmission and image quality. This produces an impact on both the detection and classification/identification of targets. With the financial participation of the U.S. Office of Naval Research (ONR), Canada's Defence Research Establishment Valcartier (DREV) is developing PRIME (Propagation Resources In the Maritime Environment), a computer model aimed at describing the overall atmospheric effects on IR imagery systems in the marine surface layer. PRIME can be used as a complement to MODTRAN to compute the effective transmittance in the marine surface layer, taking into account the lens effects caused by refraction. It also provides information on image degradation caused by both refraction and turbulence. This paper reviews the refraction phenomena that take place in the surface layer and discusses their effects on target detection and identification. We then show how PRIME can benefit detection studies and image degradation simulations.

Change in refractive index of muscle tissue during laser-induced interstitial thermotherapy.

Science.gov (United States)

Chen, Na; Chen, Meimei; Liu, Shupeng; Guo, Qiang; Chen, Zhenyi; Wang, Tingyun

2014-01-01

This paper presents a long-period fiber-grating (LPG) based Michelson interferometric refractometry to monitor the change in refractive index of porcine muscle during laser-induced interstitial thermotherapy (LITT). As the wavelength of RI interferometer alters with the change in refractive index around the probe, the LPG based refractometry is combined with LITT system to measure the change in refractive index of porcine muscle when irradiated by laser. The experimental results show the denaturation of tissue alters the refractive index significantly and the LPG sensor can be applied to monitor the tissue state during the LITT.

The Refractive Index Measurement Of Silicon Dioxide Thin Film by the Coupling Prism Method

International Nuclear Information System (INIS)

Budianto, Anwar; Hariyanto, Sigit; Subarkah

1996-01-01

Refractive index of silicon dioxide thin film that doped with phosphor (SiO 2 :P) above the pure silicon dioxide substrate has been measured by light coupling prism method. The method principle is focusing the light on coupling prism base so that the light propagates into the waveguide layer while the reflected one forms a mode in the observation plane. The SiO 2 thin film as waveguide layer has a refractive index that give the thick and refractive index relation. The He-Ne laser as light source has the wavelength λ 0,6328 μm. The refractive index measurement of the thin film with the substrate refractive index n sb = 1,47 and the thin film thick d = 2μm gives n g = 1,5534 ± 0,01136. This method can distinguish the refractive index of thin film about 6% to the refractive index of substrate

Low-Coherence Reflectometry for Refractive Index Measurements of Cells in Micro-Capillaries

Science.gov (United States)

Carpignano, Francesca; Rigamonti, Giulia; Mazzini, Giuliano; Merlo, Sabina

2016-01-01

The refractive index of cells provides insights into their composition, organization and function. Moreover, a good knowledge of the cell refractive index would allow an improvement of optical cytometric and diagnostic systems. Although interferometric techniques undoubtedly represent a good solution for quantifying optical path variation, obtaining the refractive index of a population of cells non-invasively remains challenging because of the variability in the geometrical thickness of the sample. In this paper, we demonstrate the use of infrared low-coherence reflectometry for non-invasively quantifying the average refractive index of cell populations gently confined in rectangular glass micro-capillaries. A suspension of human red blood cells in plasma is tested as a reference. As a use example, we apply this technique to estimate the average refractive index of cell populations belonging to epithelial and hematological families. PMID:27727172

Refractive outcomes after multifocal intraocular lens exchange.

Science.gov (United States)

Kim, Eric J; Sajjad, Ahmar; Montes de Oca, Ildamaris; Koch, Douglas D; Wang, Li; Weikert, Mitchell P; Al-Mohtaseb, Zaina N

2017-06-01

To evaluate the refractive outcomes after multifocal intraocular lens (IOL) exchange. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Retrospective case series. Patients had multifocal IOL explantation followed by IOL implantation. Outcome measures included type of IOL, surgical indication, corrected distance visual acuity (CDVA), and refractive prediction error. The study comprised 29 patients (35 eyes). The types of IOLs implanted after multifocal IOL explantation included in-the-bag IOLs (74%), iris-sutured IOLs (6%), sulcus-fixated IOLs with optic capture (9%), sulcus-fixated IOLs without optic capture (9%), and anterior chamber IOLs (3%). The surgical indication for exchange included blurred vision (60%), photic phenomena (57%), photophobia (9%), loss of contrast sensitivity (3%), and multiple complaints (29%). The CDVA was 20/40 or better in 94% of eyes before the exchange and 100% of eyes after the exchange (P = .12). The mean refractive prediction error significantly decreased from 0.22 ± 0.81 diopter (D) before the exchange to -0.09 ± 0.53 D after the exchange (P exchange to 0.23 D after the exchange (P exchange can be performed safely with good visual outcomes using different types of IOLs. A lower refractive prediction error and a higher likelihood of 20/40 or better vision can be achieved with the implantation of the second IOL compared with the original multifocal IOL, regardless of the final IOL position. Copyright © 2017 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Theory of supervirtual refraction interferometry

KAUST Repository

Bharadwaj, Pawan; Schuster, Gerard T.; Mallinson, Ian; Dai, Wei

2012-01-01

Inverting for the subsurface velocity distribution by refraction traveltime tomography is a well-accepted imaging method by both the exploration and earthquake seismology communities. A significant drawback, however, is that the recorded traces become noisier with increasing offset from the source position, and so accurate picking of traveltimes in far-offset traces is often prevented. To enhance the signal-to-noise ratio (SNR) of the far-offset traces, we present the theory of supervirtual refraction interferometry where the SNR of far-offset head-wave arrivals can be theoretically increased by a factor proportional to; here, N is the number of receiver or source positions associated with the recording and generation of the head-wave arrival. There are two steps to this methodology: correlation and summation of the data to generate traces with virtual head-wave arrivals, followed by the convolution of the data with the virtual traces to create traces with supervirtual head-wave arrivals. This method is valid for any medium that generates head-wave arrivals recorded by the geophones. Results with both synthetic traces and field data demonstrate the feasibility of this method. There are at least four significant benefits of supervirtual interferometry: (1) an enhanced SNR of far-offset traces so the first-arrival traveltimes of the noisy far-offset traces can be more reliably picked to extend the useful aperture of the data, (2) the SNR of head waves in a trace that arrive later than the first arrival can be enhanced for accurate traveltime picking and subsequent inversion by later-arrival traveltime tomography, (3) common receiver-pair gathers can be analysed to detect the presence of diving waves in the first arrivals, which can be used to assess the nature of the refracting boundary, and (4) the source statics term is eliminated in the correlation operations so that the timing of the virtual traces is independent of the source excitation time. This suggests the

Empirical modelling to predict the refractive index of human blood

International Nuclear Information System (INIS)

Yahya, M; Saghir, M Z

2016-01-01

Optical techniques used for the measurement of the optical properties of blood are of great interest in clinical diagnostics. Blood analysis is a routine procedure used in medical diagnostics to confirm a patient’s condition. Measuring the optical properties of blood is difficult due to the non-homogenous nature of the blood itself. In addition, there is a lot of variation in the refractive indices reported in the literature. These are the reasons that motivated the researchers to develop a mathematical model that can be used to predict the refractive index of human blood as a function of concentration, temperature and wavelength. The experimental measurements were conducted on mimicking phantom hemoglobin samples using the Abbemat Refractometer. The results analysis revealed a linear relationship between the refractive index and concentration as well as temperature, and a non-linear relationship between refractive index and wavelength. These results are in agreement with those found in the literature. In addition, a new formula was developed based on empirical modelling which suggests that temperature and wavelength coefficients be added to the Barer formula. The verification of this correlation confirmed its ability to determine refractive index and/or blood hematocrit values with appropriate clinical accuracy. (paper)

The Determinants of Early Refractive Error on School-Going Chinese Children

Directory of Open Access Journals (Sweden)

K. Jayaraman

2016-04-01

Full Text Available Refractive error is a common social issue in every walks of human life, and its prevalence recorded the highest among Chinese population, particularly among people living in southern China, Hong Kong, Thailand, Singapore, and Malaysia. Refractive error is the simplest disorder to treat and supposed to cost the effective health care intervention. The present study included 168 Chinese school-going children aged 10 to 12 years; they were selected from different schools of urban Malaysia. It was surprising to see that 112 (66.7% children had the early onset of refractive error; refractive error was also detected late among the primary school or secondary school students. The findings revealed that the determinants of refractive error among Chinese children were personal achievements and machine dependence. The possible reasons for the above significant factors emerged could be attributed to the inbuilt culture and traditions of Chinese parents who insist that their children should be hardworking and focus on school subjects so that their parents allow them to use luxury electronic devices.

Negative refraction using Raman transitions and chirality

Energy Technology Data Exchange (ETDEWEB)

Sikes, D. E.; Yavuz, D. D. [Department of Physics, 1150 University Avenue, University of Wisconsin at Madison, Madison, Wisconsin 53706 (United States)

2011-11-15

We present a scheme that achieves negative refraction with low absorption in far-off resonant atomic systems. The scheme utilizes Raman resonances and does not require the simultaneous presence of an electric-dipole transition and a magnetic-dipole transition near the same wavelength. We show that two interfering Raman tran-sitions coupled to a magnetic-dipole transition can achieve a negative index of refraction with low absorption through magnetoelectric cross-coupling. We confirm the validity of the analytical results with exact numerical simulations of the density matrix. We also discuss possible experimental implementations of the scheme in rare-earth metal atomic systems.

Integrated Microfibre Device for Refractive Index and Temperature Sensing

Directory of Open Access Journals (Sweden)

Sulaiman W. Harun

2012-08-01

Full Text Available A microfibre device integrating a microfibre knot resonator in a Sagnac loop reflector is proposed for refractive index and temperature sensing. The reflective configuration of this optical structure offers the advantages of simple fabrication and ease of sensing. To achieve a balance between responsiveness and robustness, the entire microfibre structure is embedded in low index Teflon, except for the 0.5–2 mm diameter microfibre knot resonator sensing region. The proposed sensor has exhibited a linear spectral response with temperature and refractive index. A small change in free spectral range is observed when the microfibre device experiences a large refractive index change in the surrounding medium. The change is found to be in agreement with calculated results based on dispersion relationships.

Refractive index depth profile in PMMA due to proton irradiation

International Nuclear Information System (INIS)

Szilasi, S.Z.; Rajta, I.; Budai, J.; Toth, Z.; Petrik, P.; Baradacs, E.

2006-01-01

Complete text of publication follows. During Proton Beam Writing the beam damage causes chain scissioning in the polymer resist material (e.g. PMMA (Polymethyl methacrylate)), producing smaller molecular weight chains. Hydrogen implantation also takes place at the end of range. Compaction of the sample has been observed too, which means that the sample density becomes higher at the places where proton irradiation occurred. Furthermore, P-beam Writing has been successfully used to create buried channel waveguides in PMMA [1], since proton irradiation increases the refractive index. There are two ways of fabricating waveguides using P-beam Writing, one of them applies direct micromachining of the high refractive index core followed by the coating of a lower refractive index cladding layer. In this application the refractive indices of the substrate, the core and the cladding have to be known, which should be homogeneous within the whole structure. The other method allows producing buried waveguides. In this case proton beam writing is used to modify the refractive index along the ion path in the sample, where most of the ion energy is deposited near the end of range also known as the Bragg peak. For polymers 10 -3 refractive index change has been reported, which is usually sufficient for forming waveguides. Those measurements of the refractive index change have been performed by the refracted near field technique. In this work we used ellipsometry, in order to measure the optical parameters of the P-beam treated sample near the surface, and along the Bragg curve. Ellipsometry measures the change in the polarization state of light occurring during reflection. This change is related to the quality of the reflecting surface (i.e. the physical structure, layer thicknesses, optical constants, surface roughness, etc.). >From these measurements the refractive index and the extinction coefficient can be determined rather accurately, which makes ellipsometry a powerful tool

Indications for and outcomes of tertiary referrals in refractive surgery

NARCIS (Netherlands)

Patryn, Eliza K.; Vrijman, Violette; Nieuwendaal, Carla P.; van der Meulen, Ivanka J. E.; Mourits, Maarten P.; Lapid-Gortzak, Ruth

2014-01-01

To review the spectrum of disease, symptomatology, and management offered to patients referred for a second opinion after refractive surgery. A prospective cohort study was done on all patients referred from October 1, 2006, to September 30, 2011, to a tertiary eye clinic after refractive surgery of

Modeling of mouse eye and errors in ocular parameters affecting refractive state

Science.gov (United States)

Bawa, Gurinder

Rodents eye are particularly used to study refractive error state of an eye and development of refractive eye. Genetic organization of rodents is similar to that of humans, which makes them interesting candidates to be researched upon. From rodents family mice models are encouraged over rats because of availability of genetically engineered models. Despite of extensive work that has been performed on mice and rat models, still no one is able to quantify an optical model, due to variability in the reported ocular parameters. In this Dissertation, we have extracted ocular parameters and generated schematics of eye from the raw data from School of Medicine, Detroit. In order to see how the rays would travel through an eye and the defects associated with an eye; ray tracing has been performed using ocular parameters. Finally we have systematically evaluated the contribution of various ocular parameters, such as radii of curvature of ocular surfaces, thicknesses of ocular components, and refractive indices of ocular refractive media, using variational analysis and a computational model of the rodent eye. Variational analysis revealed that variation in all the ocular parameters does affect the refractive status of the eye, but depending upon the magnitude of the impact those parameters are listed as critical or non critical. Variation in the depth of the vitreous chamber, thickness of the lens, radius of the anterior surface of the cornea, radius of the anterior surface of the lens, as well as refractive indices for the lens and vitreous, appears to have the largest impact on the refractive error and thus are categorized as critical ocular parameters. The radii of the posterior surfaces of the cornea and lens have much smaller contributions to the refractive state, while the radii of the anterior and posterior surfaces of the retina have no effect on the refractive error. These data provide the framework for further refinement of the optical models of the rat and mouse

REFractions: The Representing Equivalent Fractions Game

Science.gov (United States)

Tucker, Stephen I.

2014-01-01

Stephen Tucker presents a fractions game that addresses a range of fraction concepts including equivalence and computation. The REFractions game also improves students' fluency with representing, comparing and adding fractions.

Comparison of monochromatic aberrations in young adults with different visual acuity and refractive errors.

Science.gov (United States)

Yazar, Seyhan; Hewitt, Alex W; Forward, Hannah; McKnight, Charlotte M; Tan, Alex; Mountain, Jenny A; Mackey, David A

2014-03-01

To compare the monochromatic aberrations in a large cohort of 20-year-old Australians with differing levels of visual acuity and explore the relationship between these aberrations and refractive error. Lions Eye Institute, Perth, Western Australia, Australia. Cross-sectional analysis of a population-based cohort. Monochromatic aberrations were measured using a Zywave II wavefront aberrometer with natural pupils in a dark room. The logMAR corrected distance visual acuity (CDVA) was measured monocularly under normal illumination. Cycloplegic autorefraction was also performed. The study enrolled 2039 eyes of 1040 participants. Data from 1007 right eyes were analyzed. The median CDVA and spherical equivalent were -0.06 logMAR (interquartile range [IQR], -0.10 to 0.00) and +0.25 diopters (D) (IQR, -0.38 to 0.63), respectively. The median 6.0 mm higher-order aberration (HOA) was 0.58 μm (IQR, 0.44 to 0.79). Coma-like aberrations and 3rd-, 4th-, and 5th-order HOAs were significantly different between subjects with a CDVA of -0.10 logMAR or better and those with a CDVA worse than -0.10 logMAR. Fourth-order aberrations Z(4,-4) (P=.024) and Z(4,-2) (P=.029) and 2nd-order aberration Z(2,0) (Peyes, emmetropic eyes, and hyperopic eyes. Subjects with higher myopia had slightly higher total HOAs. The HOAs in this population were marginally higher than previously reported values. The findings confirm there is a difference in monochromatic aberrations between different vision and refractive groups. Results in this study will benefit decision-making processes in the clinical setting. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Power-controlled transition from standard to negative refraction in reorientational soft matter.

Science.gov (United States)

Piccardi, Armando; Alberucci, Alessandro; Kravets, Nina; Buchnev, Oleksandr; Assanto, Gaetano

2014-11-25

Refraction at a dielectric interface can take an anomalous character in anisotropic crystals, when light is negatively refracted with incident and refracted beams emerging on the same side of the interface normal. In soft matter subject to reorientation, such as nematic liquid crystals, the nonlinear interaction with light allows tuning of the optical properties. We demonstrate that in such material a beam of light can experience either positive or negative refraction depending on input power, as it can alter the spatial distribution of the optic axis and, in turn, the direction of the energy flow when traveling across an interface. Moreover, the nonlinear optical response yields beam self-focusing and spatial localization into a self-confined solitary wave through the formation of a graded-index waveguide, linking the refractive transition to power-driven readdressing of copolarized guided-wave signals, with a number of output ports not limited by diffraction.

Babinet's principle in double-refraction systems

Science.gov (United States)

Ropars, Guy; Le Floch, Albert

2014-06-01

Babinet's principle applied to systems with double refraction is shown to involve spatial interchanges between the ordinary and extraordinary patterns observed through two complementary screens. As in the case of metamaterials, the extraordinary beam does not follow the Snell-Descartes refraction law, the superposition principle has to be applied simultaneously at two points. Surprisingly, by contrast to the intuitive impression, in the presence of the screen with an opaque region, we observe that the emerging extraordinary photon pattern, which however has undergone a deviation, remains fixed when a natural birefringent crystal is rotated while the ordinary one rotates with the crystal. The twofold application of Babinet's principle implies intensity and polarization interchanges but also spatial and dynamic interchanges which should occur in birefringent metamaterials.

Polymer microfiber bridging Bi-tapered refractive index sensor based on evanescent field

Science.gov (United States)

Lv, Ri-Qing; Wang, Qi; Wang, Bo-Tao; Liu, Yu; Kong, Lingxin

2018-05-01

A PDMS/graphene enhanced PMMA micro optical waveguide sensor is reported in terms of fabrication method and optical characteristics. The micro optical waveguide with a diameter of 6 μm and a length of 800 μm is used as the sensing probe to realize refractive index (RI) measurement suspended in NaCl solutions with different concentrations. Experimental results show that the refractive index sensing sensitivity can reach 2027.97 nm/RIU within the refractive index ranging from 1.3333-1.3426. Research results show that PMMA/graphene micro optical waveguide doped with PDMS is an excellent high sensitive sensing technology in refractive index detection field.

Analysis of the hologram recording on the novel chloride photo-thermo-refractive glass

Science.gov (United States)

Ivanov, S. A.; Nikonorov, N. V.; Dubrovin, V. D.; Krykova, V. A.

2017-05-01

In this research, we present new holographic material based on fluoride photo-thermo-refractive glass(PTR) - chloride PTR glass. One of the benefit of this type of PTR glass is positive refractive index change. During this work, for the first-time volume Bragg gratings were recorded in this kind of material. The first experiments revealed that such gratings are mixed i.e. possess both absorption and phase components. Complex analysis shows that both refractive index and absorption coefficient are modulated inside the grating structure. We found out that at first there is no strict dependence of the refractive index change from dosage, but as we continue the process of thermal treatment - dependence is appear. Exposure influence on the refractive index change for this glass differs from fluoride one and shows some sort of saturation after the exposure of 4-6 J/cm2 . We distinguished refractive index change and absorption coefficient change and observed both behavior with increasing thermal treatment time. We found out that the increase of thermal treatment time results in the significant refractive index change. At the same time the absorption does `not practically change. It was found that maximum modulation of refractive index is comparable with fluoride PTR glass and achieves value of 1600 ppm. The modulation of absorption is equal to induced absorption caused by silver nanoparticles and depends from reading wavelength. Our study shows that almost all absorption is modulated inside the grating.

Diagnostics of gas behind shock waves by refractive optical techniques

International Nuclear Information System (INIS)

Blaha, J.

In a brief outline of optical methods for measuring neutral gas and plasma parameters, techniques are specifically dealt with based on the interferometric measurement of the refractive index. The investigation is shown of gas density changes in a shock tube using the optical Mach-Zehnder interferometer. While in a neutral gas the refractive index is determined by gas density, in a plasma the effects of all components, ie., electrons, ions and atoms are additive. The contributions to refraction from the various components may, in view of the different character and frequencies of the components, be resolved by measurement on more than one wavelength. (J.U.)

Beyond Snel's law: Refraction of a nano-beam of light

International Nuclear Information System (INIS)

Sun Wenbo; Videen, Gorden; Lin Bing; Hu Yongxiang; Fu Qiang

2011-01-01

The refraction of a localized narrow beam is significantly different from that of a plane wave. As the beam width decreases to be in the order of the wavelength, the refraction behavior deviates noticeably from Snel's law, and when the width of a light beam is smaller than about one fifth of the wavelength of the incident light, finite-difference time-domain simulations demonstrate that refraction becomes negligible. That is, the narrow light beam retains its propagation direction even after entering another medium at an oblique angle. The result reveals novel features of nano-beams and may have applications in precise biomedical measurement or micro optical device.

Observations of Anomalous Refraction with Co-housed Telescopes

Science.gov (United States)

Taylor, Malinda S.; McGraw, J. T.; Zimmer, P. C.

2013-01-01

Anomalous refraction is described as a low frequency, large angular scale motion of the entire image plane with respect to the celestial coordinate system as observed and defined by previous astrometric catalogs. These motions of typically several tenths of an arcsecond with timescales on the order of ten minutes are ubiquitous to drift-scan ground-based astrometric measurements regardless of location or telescopes used and have been attributed to meter scale slowly evolving coherent dynamical structures in the boundary-layer below 60 meters. The localized nature of the effect and general inconsistency of the motions seen by even closely spaced telescopes in individual domes has led to the hypothesis that the dome or other type of telescope housing may be responsible. This hypothesis is tested by observing anomalous refraction using two telescopes housed in a single roll-off roof observatory building with the expected outcome that the two telescopes will see correlated anomalous refraction induced motions.

Homodyne chiral polarimetry for measuring thermo-optic refractive index variations.

Science.gov (United States)

Twu, Ruey-Ching; Wang, Jhao-Sheng

2015-10-10

Novel reflection-type homodyne chiral polarimetry is proposed for measuring the refractive index variations of a transparent plate under thermal impact. The experimental results show it is a simple and useful method for providing accurate measurements of refractive index variations. The measurement can reach a resolution of 7×10-5.

Prevalence of refractive errors among junior high school students in ...

African Journals Online (AJOL)

Among school children, uncorrected refractive errors have a considerable impact on their participation and learning in class. The aim of this study was to assess the prevalence of refractive error among students in the Ejisu-Juabeng Municipality of Ghana. A survey with multi-stage sampling was undertaken. We interviewed ...

Super-virtual refraction interferometry: an engineering field data example

KAUST Repository

Hanafy, Sherif M.

2012-10-01

The theory of super-virtual refraction interferometry (SVI) was recently developed to enhance the signal-to-noise ratio (SNR) of far-offset traces in refraction surveys. This enhancement of the SNR is proportional to √N and can be as high as N if an iterative procedure is used. Here N is the number of post-critical shot positions that coincides with the receiver locations. We now demonstrate the SNR enhancement of super-virtual refraction traces for one engineering-scale synthetic data and two field seismic data sets. The field data are collected over a normal fault in Saudi Arabia. Results show that both the SNR of the super-virtual data set and the number of reliable first-arrival traveltime picks are significantly increased. © 2012 European Association of Geoscientists & Engineers.

Super-virtual refraction interferometry: an engineering field data example

KAUST Repository

Hanafy, Sherif M.; Alhagan, Ola

2012-01-01

The theory of super-virtual refraction interferometry (SVI) was recently developed to enhance the signal-to-noise ratio (SNR) of far-offset traces in refraction surveys. This enhancement of the SNR is proportional to √N and can be as high as N if an iterative procedure is used. Here N is the number of post-critical shot positions that coincides with the receiver locations. We now demonstrate the SNR enhancement of super-virtual refraction traces for one engineering-scale synthetic data and two field seismic data sets. The field data are collected over a normal fault in Saudi Arabia. Results show that both the SNR of the super-virtual data set and the number of reliable first-arrival traveltime picks are significantly increased. © 2012 European Association of Geoscientists & Engineers.

The effect of instrument alignment on peripheral refraction measurements by automated optometer.

Science.gov (United States)

Ehsaei, Asieh; Chisholm, Catharine M; Mallen, Edward A H; Pacey, Ian E

2011-07-01

Interest in peripheral refraction measurement has grown in recent years in response to the insight it may provide into myopia development. In light of the likely increase in the clinical use of open-field autorefractors for peripheral refraction measurements, the question of instrument alignment and its impact on the accuracy of refraction measurements is raised. The aim of this study was to investigate the accuracy and precision when an open-field device was moved away from alignment with the corneal reflex towards the pupil margins, and to determine the optimum alignment position for peripheral refraction measurements. Autorefractions were performed on the right eyes of 10 healthy participants using the Shin-Nippon NVision-K 5001 autorefractor. At least five measurements were taken with the subject fixating a distance target in the primary position of gaze, and then four peripheral fixation targets located along the horizontal meridian (10° and 20° eccentricities in the nasal and temporal retina). Measurements were taken at seven alignment positions across the pupil for each fixation angle. Refraction was recorded as the spherical and cylindrical power. The central objective refraction achieved under cycloplegia based on the autorefraction result for the whole sample, ranged between -5.62 D and +1.85 D for the value of sphere, with a maximum astigmatism of -1.00 D. Acceptable alignment position range varied with fixation angle but was -1.0 to +1.0 mm in width across the pupil. Peripheral refraction measurements centred on the entrance pupil were as reliable as those centred on the corneal reflex. Our data suggest that for peripheral refraction measurements, there is a range of acceptable positions and operators can be confident of the validity of results obtained if aligned half way between the pupil centre and corneal reflex. The alignment becomes more critical at greater eccentricities. Ophthalmic & Physiological Optics © 2011 The College of Optometrists.

Improvement of visual acuity by refraction in a low-vision population.

Science.gov (United States)

Sunness, Janet S; El Annan, Jaafar

2010-07-01

Refraction often may be overlooked in low-vision patients, because the main cause of vision decrease is not refractive, but rather is the result of underlying ocular disease. This retrospective study was carried out to determine how frequently and to what extent visual acuity is improved by refraction in a low-vision population. Cross-sectional study. Seven hundred thirty-nine low-vision patients seen for the first time. A database with all new low-vision patients seen from November 2005 through June 2008 recorded presenting visual acuity using an Early Treatment Diabetic Retinopathy Study chart; it also recorded the best-corrected visual acuity (BCVA) if it was 2 lines or more better than the presenting visual acuity. Retinoscopy was carried out on all patients, followed by manifest refraction. Improvement in visual acuity. Median presenting acuity was 20/80(-2) (interquartile range, 20/50-20/200). There was an improvement of 2 lines or more of visual acuity in 81 patients (11% of all patients), with 22 patients (3% of all patients) improving by 4 lines or more. There was no significant difference in age or in presenting visual acuity between the group that did not improve by refraction and the group that did improve. When stratified by diagnosis, the only 2 diagnoses with a significantly higher rate of improvement than the age-related macular degeneration group were myopic degeneration and progressive myopia (odds ratio, 4.8; 95% confidence interval [CI], 3.0-6.7) and status post-retinal detachment (odds ratio, 7.1; 95% CI, 5.2-9.0). For 5 patients (6% of those with improvement), the eye that was 1 line or more worse than the fellow eye at presentation became the eye that was 1 line or more better than the fellow eye after refraction. A significant improvement in visual acuity was attained by refraction in 11% of the new low-vision patients. Improvement was seen across diagnoses and the range of presenting visual acuity. The worse-seeing eye at presentation may

Intraocular lens calculation adjustment after laser refractive surgery using Scheimpflug imaging.

Science.gov (United States)

Schuster, Alexander K; Schanzlin, David J; Thomas, Karin E; Heichel, Christopher W; Purcell, Tracy L; Barker, Patrick D

2016-02-01

To test a new method of intraocular lens (IOL) calculation after corneal refractive surgery using Scheimpflug imaging (Pentacam HR) and partial coherence interferometry (PCI) (IOLMaster) that does not require historical data; that is, the Schuster/Schanzlin-Thomas-Purcell (SToP) IOL calculator. Shiley Eye Center, San Diego, California, and Walter Reed National Military Medical Center, Bethesda, Maryland, USA. Retrospective data analysis and validation study. Data were retrospectively collected from patient charts including data from Scheimpflug imaging and refractive history. Target refraction was calculated using PCI and the Holladay 1 and SRK/T formulas. Regression analysis was performed to explain the deviation of the target refraction, taking into account the following influencing factors: ratio of posterior-to-anterior corneal radius, axial length (AL), and anterior corneal radius. The regression analysis study included 61 eyes (39 patients) that had laser in situ keratomileusis (57 eyes) or photorefractive keratectomy (4 eyes) and subsequent cataract. Two factors were found that explained the deviation of the target refraction using the Holladay 1 formula; that is, the ratio of the corneal radii and the AL and the ratio of corneal radii for the SRK/T formula. A new IOL adjustment calculator was derived and validated at a second center using 14 eyes (10 patients). The error in IOL calculation for normal eyes after laser refractive treatment was related to the ratio of posterior-to-anterior corneal radius. A formula requiring Scheimpflug data and suggested IOL power only yielded an improved postoperative result for patients with previous corneal laser refractive surgery having cataract surgery. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2016 ASCRS and ESCRS. All rights reserved.

Dependency between light intensity and refractive development under light-dark cycles.

Science.gov (United States)

Cohen, Yuval; Belkin, Michael; Yehezkel, Oren; Solomon, Arieh S; Polat, Uri

2011-01-01

The emmetropization process involves fine-tuning the refractive state by altering the refractive components toward zero refraction. In this study, we provided light-dark cycle conditions at several intensities and examined the effect of light intensity on the progression of chicks' emmetropization. Chicks under high-, medium-, and low-light intensities (10,000, 500, and 50 lux, respectively) were followed for 90 days by retinoscopy, keratometry, as well as ultrasound measurements. Emmetropization was reached from days 30-50 and from days 50-60 for the low- and medium-intensity groups, respectively. On day 90, most chicks in the low-intensity group were myopic, with a mean refraction of -2.41D (95% confidence interval (CI) -2.9 to -1.8D), whereas no chicks in the high-intensity group developed myopia, but they exhibited a stable mean hyperopia of +1.1D. The medium-intensity group had a mean refraction of +0.03D. The low-intensity group had a deeper vitreous chamber depth and a longer axial length compared with the high-intensity group, and shifted refraction to the myopic side. The low-intensity group had a flatter corneal curvature, a deeper anterior chamber, and a thinner lens compared with the high-intensity group, and shifted refraction to the hyperopic side. In all groups the corneal power was correlated with the three examined levels of log light intensity for all examined times (e.g., day 20 r = 0.6 P light-dark cycles, light intensity is an environmental factor that modulates the process of emmetropization, and the low intensity of ambient light is a risk factor for developing myopia. Copyright © 2010 Elsevier Ltd. All rights reserved.

Autorefraction versus subjective refraction in a radially asymmetric multifocal intraocular lens

NARCIS (Netherlands)

Linden, J.W.M. van der; Vrijman, V.; El-Saady, R.; Meulen, I.J. van der; Mourits, M.P.; Lapid-Gortzak, R.

2014-01-01

PURPOSE: To evaluate whether the automated refraction (AR) correlates with subjective manifest (MR) refraction in eyes implanted with radially asymmetric multifocal intraocular lens (IOLs). METHODS: This retrospective study evaluated 52 eyes (52 patients) implanted with a radially asymmetric

Nature of the Refractive Errors in Rhesus Monkeys (Macaca mulatta) with Experimentally Induced Ametropias

Science.gov (United States)

Qiao-Grider, Ying; Hung, Li-Fang; Kee, Chea-su; Ramamirtham, Ramkumar; Smith, Earl L.

2010-01-01

We analyzed the contribution of individual ocular components to vision-induced ametropias in 210 rhesus monkeys. The primary contribution to refractive-error development came from vitreous chamber depth; a minor contribution from corneal power was also detected. However, there was no systematic relationship between refractive error and anterior chamber depth or between refractive error and any crystalline lens parameter. Our results are in good agreement with previous studies in humans, suggesting that the refractive errors commonly observed in humans are created by vision-dependent mechanisms that are similar to those operating in monkeys. This concordance emphasizes the applicability of rhesus monkeys in refractive-error studies. PMID:20600237

Corrective Techniques and Future Directions for Treatment of Residual Refractive Error Following Cataract Surgery

Science.gov (United States)

Moshirfar, Majid; McCaughey, Michael V; Santiago-Caban, Luis

2015-01-01

Postoperative residual refractive error following cataract surgery is not an uncommon occurrence for a large proportion of modern-day patients. Residual refractive errors can be broadly classified into 3 main categories: myopic, hyperopic, and astigmatic. The degree to which a residual refractive error adversely affects a patient is dependent on the magnitude of the error, as well as the specific type of intraocular lens the patient possesses. There are a variety of strategies for resolving residual refractive errors that must be individualized for each specific patient scenario. In this review, the authors discuss contemporary methods for rectification of residual refractive error, along with their respective indications/contraindications, and efficacies. PMID:25663845

Anomalous refraction of light through slanted-nanoaperture arrays on metal surface

International Nuclear Information System (INIS)

Kim, Myungji; Jung, Yun Suk; Xi, Yonggang; Kim, Hong Koo

2015-01-01

We report a nanoapertured metal surface that demonstrates anomalous refraction of light for a wide range of incident angles. A nanoslit aperture is designed to serve as a tilted vertical-dipole whose radiation pattern orients to a glancing angle direction to substrate. An array of such slanted nanoslits formed in a metal film redirects an incident beam into the direction of negative refraction angle: the aperture-transmitted wave makes a far-field propagation to the tilt-oriented direction of radiation pattern. The thus-designed nanoaperture array demonstrates the −1st order diffraction (i.e., to the negative refraction-angle direction) with well-suppressed background transmission (the zero-order direct transmission and other higher-order diffractions). Engineering the radiation pattern of nanoaperture offers an approach to overcoming the limits of conventional diffractive/refractive optics and complementing metasurface-based nano-optics

Refraction in exoplanet atmospheres. Photometric signatures, implications for transmission spectroscopy, and search in Kepler data

Science.gov (United States)

Alp, D.; Demory, B.-O.

2018-01-01

Context. Refraction deflects photons that pass through atmospheres, which affects transit light curves. Refraction thus provides an avenue to probe physical properties of exoplanet atmospheres and to constrain the presence of clouds and hazes. In addition, an effective surface can be imposed by refraction, thereby limiting the pressure levels probed by transmission spectroscopy. Aims: The main objective of the paper is to model the effects of refraction on photometric light curves for realistic planets and to explore the dependencies on atmospheric physical parameters. We also explore under which circumstances transmission spectra are significantly affected by refraction. Finally, we search for refraction signatures in photometric residuals in Kepler data. Methods: We use the model of Hui & Seager (2002, ApJ, 572, 540) to compute deflection angles and refraction transit light curves, allowing us to explore the parameter space of atmospheric properties. The observational search is performed by stacking large samples of transit light curves from Kepler. Results: We find that out-of-transit refraction shoulders are the most easily observable features, which can reach peak amplitudes of 10 parts per million (ppm) for planets around Sun-like stars. More typical amplitudes are a few ppm or less for Jovians and at the sub-ppm level for super-Earths. In-transit, ingress, and egress refraction features are challenging to detect because of the short timescales and degeneracies with other transit model parameters. Interestingly, the signal-to-noise ratio of any refraction residuals for planets orbiting Sun-like hosts are expected to be similar for planets orbiting red dwarfs and ultra-cool stars. We also find that the maximum depth probed by transmission spectroscopy is not limited by refraction for weakly lensing planets, but that the incidence of refraction can vary significantly for strongly lensing planets. We find no signs of refraction features in the stacked Kepler

Refractive index modulation in polymer film doped with diazo Meldrum's acid

Science.gov (United States)

Zanutta, Alessio; Villa, Filippo; Bertarelli, Chiara; Bianco, Andrea

2016-08-01

Diazo Meldrum's acid undergoes a photoreaction induced by UV light and it is used as photosensitizer in photoresists. Upon photoreaction, a change in refractive index occurs, which makes this system interesting for volume holography. We report on the sublimation effect at room temperature and the effect of photoirradiation on the refractive index in thin films of CAB (Cellulose acetate butyrate) doped with different amount of diazo Meldrum's acid. A net modulation of the refractive index of 0.01 is achieved with 40% of doping ratio together with a reduction of the film thickness.

Infrasonic ray tracing applied to mesoscale atmospheric structures: refraction by hurricanes.

Science.gov (United States)

Bedard, Alfred J; Jones, R Michael

2013-11-01

A ray-tracing program is used to estimate the refraction of infrasound by the temperature structure of the atmosphere and by hurricanes represented by a Rankine-combined vortex wind plus a temperature perturbation. Refraction by the hurricane winds is significant, giving rise to regions of focusing, defocusing, and virtual sources. The refraction of infrasound by the temperature anomaly associated with a hurricane is small, probably no larger than that from uncertainties in the wind field. The results are pertinent to interpreting ocean wave generated infrasound in the vicinities of tropical cyclones.

Physical and electrical characteristics of silicon oxynitride films with various refractive indices

Energy Technology Data Exchange (ETDEWEB)

Liao, Jeng-Hwa; Hsieh, Jung-Yu; Lin, Hsing-Ju; Tang, Wei-Yao; Chiang, Chun-Ling; Yang, Ling-Wu; Yang, Tahone; Chen, Kuang-Chao; Lu, Chih-Yuan [Macronix International Co. Ltd, No 16, Li-Hsin Road, Hsinchu Science Park, Hsinchu 300, Taiwan (China); Lo, Yun-Shan; Wu, Tai-Bor, E-mail: jhliao@mxic.com.t [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan (China)

2009-09-07

This study explores the relationship between both the physical and the electrical characteristics of silicon oxynitride (SiON) films and the refractive index. The single wafer rapid thermal process modules were used for low pressure chemical vapour deposition of SiON films. A series of SiON films with refractive index between 1.50 and 1.83 were fabricated. Fourier transform infrared absorption spectroscopy and x-ray photoelectron spectroscopy identified the chemical bonding configurations of different SiON films: the Si-N bonds are replaced by Si-O bonds as the refractive index of the SiON films declines. Moreover, the Si atomic ratio is kept between 35% and 40% while the oxygen atomic ratio increases and the nitrogen atomic ratio decreases as the refractive index of the SiON film declines. The electrical characteristics of different SiON-based silicon-oxide-nitride-oxide-silicon (SONOS) devices suggest that (1) the dielectric constant increases with increasing refractive index of the SiON film and (2) the charge-trap density is inversely proportional to the oxygen concentration in the SiON film. Based on these results, the SiON films with various refractive indices can provide a wider application for silicon-based devices, such as SONOS and MOS devices.

Physical and electrical characteristics of silicon oxynitride films with various refractive indices

International Nuclear Information System (INIS)

Liao, Jeng-Hwa; Hsieh, Jung-Yu; Lin, Hsing-Ju; Tang, Wei-Yao; Chiang, Chun-Ling; Yang, Ling-Wu; Yang, Tahone; Chen, Kuang-Chao; Lu, Chih-Yuan; Lo, Yun-Shan; Wu, Tai-Bor

2009-01-01

This study explores the relationship between both the physical and the electrical characteristics of silicon oxynitride (SiON) films and the refractive index. The single wafer rapid thermal process modules were used for low pressure chemical vapour deposition of SiON films. A series of SiON films with refractive index between 1.50 and 1.83 were fabricated. Fourier transform infrared absorption spectroscopy and x-ray photoelectron spectroscopy identified the chemical bonding configurations of different SiON films: the Si-N bonds are replaced by Si-O bonds as the refractive index of the SiON films declines. Moreover, the Si atomic ratio is kept between 35% and 40% while the oxygen atomic ratio increases and the nitrogen atomic ratio decreases as the refractive index of the SiON film declines. The electrical characteristics of different SiON-based silicon-oxide-nitride-oxide-silicon (SONOS) devices suggest that (1) the dielectric constant increases with increasing refractive index of the SiON film and (2) the charge-trap density is inversely proportional to the oxygen concentration in the SiON film. Based on these results, the SiON films with various refractive indices can provide a wider application for silicon-based devices, such as SONOS and MOS devices.

Autorefraction versus subjective refraction in a radially asymmetric multifocal intraocular lens

NARCIS (Netherlands)

van der Linden, Jan Willem; Vrijman, Violette; Al-Saady, Rana; El-Saady, Rana; van der Meulen, Ivanka J.; Mourits, Maarten P.; Lapid-Gortzak, Ruth

2014-01-01

To evaluate whether the automated refraction (AR) correlates with subjective manifest (MR) refraction in eyes implanted with radially asymmetric multifocal intraocular lens (IOLs). This retrospective study evaluated 52 eyes (52 patients) implanted with a radially asymmetric multifocal IOL (LS-312

High-negative effective refractive index of silver nanoparticles system in nanocomposite films

Science.gov (United States)

Altunin, Konstantin K.; Gadomsky, Oleg N.

2012-03-01

We have proved on the basis of the experimental optical reflection and transmission spectra of the nanocomposite film of poly(methyl methacrylate) with silver nanoparticles that (PMMA + Ag) nanocomposite films have quasi-zero refractive indices in the optical wavelength range. We show that to achieve quasi-zero values of the complex index of refraction of composite materials is necessary to achieve high-negative effective refractive index in the system of spherical silver nanoparticles.

THz-induced ultrafast modulation of NIR refractive index of silicon

DEFF Research Database (Denmark)

Tarekegne, Abebe Tilahun; Hirori, Hideki; Iwaszczuk, Krzysztof

2016-01-01

We measure THz-induced change in refractive index of ∼5×10−3 in high resistivity silicon at 800 nm which indicates generation of high density of free carriers. The change in refractive index increases by more than 30 times with high initial carrier density set by optical excitation compared to op...

Super-virtual refraction interferometry: Theory

KAUST Repository

Bharadwaj, Pawan

2011-01-01

Inverting for the subsurface velocity distribution by refraction traveltime tomography is a well-accepted imaging method by both the exploration and earthquake seismology communities. A significant drawback, however, is that the recorded traces become noisier with increasing offset from the source position, and so prevents accurate picking of traveltimes in far-offset traces. To enhance the signal-to-noise ratio of the far-offset traces, we present the theory of super-virtual refraction interferometry where the signal-to-noise ratio (SNR) of far-offset head-wave arrivals can be theoretically increased by a factor proportional to N; here, N is the number of receiver and source positions associated with the recording and generation of the head-wave arrival. There are two steps to this methodology: correlation and summation of the data to generate traces with virtual head-wave arrivals, followed by the convolution of the data with the virtual traces to create traces with super-virtual head-wave arrivals. This method is valid for any medium that generates head-wave arrivals. There are at least three significant benefits to this methodology: 1). enhanced SNR of far-offset traces so the first-arrival traveltimes of the noisy far-offset traces can be more reliably picked to extend the useful aperture of data, 2). the SNR of head waves in a trace that arrive after the first arrival can be enhanced for accurate traveltime picking and subsequent inversion by traveltime tomography, and 3). common receiver-pair gathers can be analyzed to detect the presence of diving waves in the first arrivals, which can be used to assess the nature of the refracting boundary. © 2011 Society of Exploration Geophysicists.

Refractive Surgery: Malpractice Litigation Outcomes.

Science.gov (United States)

Custer, Benjamin L; Ballard, Steven R; Carroll, Robert B; Barnes, Scott D; Justin, Grant A

2017-10-01

To review data on malpractice claims related to refractive surgery to identify common allegations and injuries and financial outcomes. The WestlawNext database was reviewed for all malpractice lawsuits/settlements related to refractive eye surgery. Data evaluated included patient demographics, type of operation performed, plaintiff allegation, nature of injury, and litigation outcomes. A total of 167 cases met the inclusion criteria, of which 108 cases (64.7%) were found to be favorable and 59 cases (35.3%) unfavorable to the defendant. A total of 141 cases were tried by a jury with 108 cases (76.4%) favorable and 33 cases (23.6%) unfavorable to the defendant. Laser in situ keratomileusis was performed in 127 cases (76%). The most common allegations were negligence in treatment or surgery in 127 cases (76%) and lack of informed consent in 83 cases (49.7%). For all cases, the need for future surgery (P = 0.0001) and surgery resulting in keratoconus (P = 0.05) were more likely to favor the plaintiff. In jury verdict decisions, cases in which failure to diagnose a preoperative condition was alleged favored the defendant (P = 0.03), whereas machine malfunction (P = 0.05) favored the plaintiff. After adjustment for inflation, the overall mean award was $1,287,872. Jury verdicts and settlements led to mean awards of $1,604,801 and $826,883, respectively. Malpractice litigation in refractive surgery tends to favor the defendant. However, large awards and settlements were given in cases that were favorable to the plaintiff. The need for future surgery and surgery leading to keratoconus increased the chance of an unfavorable outcome.

Spherical equivalent refractive error in preschool children from a population with a high prevalence of astigmatism.

Science.gov (United States)

Dobson, Velma; Harvey, Erin M; Miller, Joseph M

2007-02-01

To describe spherical equivalent (sph eq) refractive errors in preschool members of a Native American tribe with a high prevalence of astigmatism. Cycloplegic autorefraction measurements were obtained for 819 three- and four-year-old Tohono O'odham children, with follow-up measurements in 146 after 4 to 8 years. Mean sph eq was significantly more hyperopic in the astigmatic group than in the non-astigmatic group (1.24 vs. 0.87 D). At follow-up, prevalence of hyperopic sph eq and hyperopic astigmatism had significantly decreased, and prevalence of emmetropic/myopic sph eq and myopic astigmatism had significantly increased. The decrease in mean sph eq was similar in astigmats and non-astigmats. Astigmatism did not change over time. Most preschool children in this highly astigmatic population are hyperopic, with astigmats showing higher mean hyperopic sph eq than non-astigmats. Astigmats and non-astigmats show a similar decrease in amount of hyperopic sph eq over follow-up of 4 to 8 years.

Refractive error assessment: influence of different optical elements and current limits of biometric techniques.

Science.gov (United States)

Ribeiro, Filomena; Castanheira-Dinis, Antonio; Dias, Joao Mendanha

2013-03-01

To identify and quantify sources of error on refractive assessment using exact ray tracing. The Liou-Brennan eye model was used as a starting point and its parameters were varied individually within a physiological range. The contribution of each parameter to refractive error was assessed using linear regression curve fits and Gaussian error propagation analysis. A MonteCarlo analysis quantified the limits of refractive assessment given by current biometric measurements. Vitreous and aqueous refractive indices are the elements that influence refractive error the most, with a 1% change of each parameter contributing to a refractive error variation of +1.60 and -1.30 diopters (D), respectively. In the phakic eye, axial length measurements taken by ultrasound (vitreous chamber depth, lens thickness, and anterior chamber depth [ACD]) were the most sensitive to biometric errors, with a contribution to the refractive error of 62.7%, 14.2%, and 10.7%, respectively. In the pseudophakic eye, vitreous chamber depth showed the highest contribution at 53.7%, followed by postoperative ACD at 35.7%. When optic measurements were considered, postoperative ACD was the most important contributor, followed by anterior corneal surface and its asphericity. A MonteCarlo simulation showed that current limits of refractive assessment are 0.26 and 0.28 D for the phakic and pseudophakic eye, respectively. The most relevant optical elements either do not have available measurement instruments or the existing instruments still need to improve their accuracy. Ray tracing can be used as an optical assessment technique, and may be the correct path for future personalized refractive assessment. Copyright 2013, SLACK Incorporated.

Negative Refraction Using Frequency-Tuned Oxide Multilayer Structure

Directory of Open Access Journals (Sweden)

Yalin Lu

2008-01-01

Full Text Available An oxide-based multilayer structure was proposed to realize negative refraction. The multilayer composes of alternative layers having negative permittivity and negative permeability, respectively. In order to realize negative refraction, their dielectric and magnetic resonances of layers will be tuned to the frequency as close as possibly via changing their temperature, composition, structure, and so forth. Such oxide-based NIMs are attractive for their potential applications as optical super lenses, imagers, optical cloaking, sensors, and so forth, those are required with low-loss, low-cost, and good fabrication flexibility.

Study of the refractive index of gasoline+alcohol pseudo-binary mixtures

Directory of Open Access Journals (Sweden)

Nita Irina

2017-02-01

Full Text Available The properties of gasoline change as a result of blending with a bioalcohol, affecting the behavior of the pseudo-binary system. The aim of this paper is to present experimental data of the refractive index for pseudobinary mixtures of a reformate gasoline with ethanol, isopropanol and n-butanol over the entire composition range and for temperature ranging from 293.15 K to 313.15 K. The accuracy of different equations to predict the refractive index of the mixtures was tested. The best prediction accuracy (the lower AAD corresponded to Eykman and Lorentz-Lorenz mixing rules. A logarithmic equation proposed to correlate the refractive index with composition and temperature of gasoline+alcohol mixtures showed a good accuracy (the absolute average deviation AAD < 0.052%. The deviations in refractive index for investigated systems are negative over the entire composition range and at all investigated temperatures.

Prevalence of refraction errors and color blindness in heavy vehicle drivers.

Science.gov (United States)

Erdoğan, Haydar; Ozdemir, Levent; Arslan, Seher; Cetin, Ilhan; Ozeç, Ayşe Vural; Cetinkaya, Selma; Sümer, Haldun

2011-01-01

To investigate the frequency of eye disorders in heavy vehicle drivers. A cross-sectional type study was conducted between November 2004 and September 2006 in 200 driver and 200 non-driver persons. A complete ophthalmologic examination was performed, including visual acuity, and dilated examination of the posterior segment. We used the auto refractometer for determining refractive errors. According to eye examination results, the prevalence of the refractive error was 21.5% and 31.3% in study and control groups respectively (P<0.05). The most common type of refraction error in the study group was myopic astigmatism (8.3%) while in the control group simple myopia (12.8%). Prevalence of dyschromatopsia in the rivers, control group and total group was 2.2%, 2.8% and 2.6% respectively. A considerably high number of drivers are in lack of optimal visual acuity. Refraction errors in drivers may impair the traffic security.

Refractive indices of ternary liquid mixtures containing aliphatic alcohols at several temperatures

Directory of Open Access Journals (Sweden)

Sovilj Milan N.

2005-01-01

Full Text Available The refractive indices of ternary liquid mixtures (2-propanol+2-butanol+ethanol and (chloroform+2-propanol+2-butanol were measured at 20, 25, 30, and 35°C, and atmospheric pressure. The results were used to calculate the refractive index deviations over the entire mole fraction range for the mixtures. The refractive index deviations for the ternary mixtures were further fitted to empirical correlations (Cibulka Nagata-Tamura, and Lopez et al to estimate the ternary fitting parameters. Standard deviations and average percentage deviations from the regression lines are shown. The best fit was obtained by the Nagata-Tamura empirical correlation. Some of the existing predictive equations for the refractive index deviations (Tsao-Smith, Köhler, and Colinet were tested.

Prevalence of refractive errors in the European adult population: the Gutenberg Health Study (GHS).

Science.gov (United States)

Wolfram, Christian; Höhn, René; Kottler, Ulrike; Wild, Philipp; Blettner, Maria; Bühren, Jens; Pfeiffer, Norbert; Mirshahi, Alireza

2014-07-01

To study the distribution of refractive errors among adults of European descent. Population-based eye study in Germany with 15010 participants aged 35-74 years. The study participants underwent a detailed ophthalmic examination according to a standardised protocol. Refractive error was determined by an automatic refraction device (Humphrey HARK 599) without cycloplegia. Definitions for the analysis were myopia +0.5 D, astigmatism >0.5 cylinder D and anisometropia >1.0 D difference in the spherical equivalent between the eyes. Exclusion criterion was previous cataract or refractive surgery. 13959 subjects were eligible. Refractive errors ranged from -21.5 to +13.88 D. Myopia was present in 35.1% of this study sample, hyperopia in 31.8%, astigmatism in 32.3% and anisometropia in 13.5%. The prevalence of myopia decreased, while the prevalence of hyperopia, astigmatism and anisometropia increased with age. 3.5% of the study sample had no refractive correction for their ametropia. Refractive errors affect the majority of the population. The Gutenberg Health Study sample contains more myopes than other study cohorts in adult populations. Our findings do not support the hypothesis of a generally lower prevalence of myopia among adults in Europe as compared with East Asia.

Investigation of the refractive status of preschool children in Xiantao, Hubei Province

OpenAIRE

Nian Guan; Hao-Ming Chen; Zhi-Guang Hu

2014-01-01

AIM: To investigate the refractive status of the preschool children in Xiantao, Hubei Province in order to find out the abnormal refraction error beyond the physiological range. METHODS: In this cross-sectional study, we investigated preschool children in kindergartens and the scattered ones were 12 716(25 432 eyes)ranging from 6mo～6 years old. 1 581 children(3 162 eyes)were diagnosed ametropia by Suresight refractive screening instrument, which were confirmed again after mydriasis optometry....

Refractive indices of CaF2 single crystals under elastic shock loading

Science.gov (United States)

Li, Y.; Zhou, X. M.; Liu, C. L.; Luo, S. N.

2017-07-01

Refractive indices and Hugoniots of CaF2 single crystals are investigated by laser displacement interferometry under shock loading below 5 GPa. Birefringence is observed for the [110] loading. We obtain the Hugoniot equation of states for [100], [110] and [111], and refractive indices for these orientations with consideration of their polarization. The measured refractive indices are in reasonable agreement with predictions based on the piezo-optic theory, and are used to refine the elasto-optic coefficients.

Rigorous theoretical framework for particle sizing in turbid colloids using light refraction.

Science.gov (United States)

García-Valenzuela, Augusto; Barrera, Rubén G; Gutierrez-Reyes, Edahí

2008-11-24

Using a non-local effective-medium approach, we analyze the refraction of light in a colloidal medium. We discuss the theoretical grounds and all the necessary precautions to design and perform experiments to measure the effective refractive index in dilute colloids. As an application, we show that it is possible to retrieve the size of small dielectric particles in a colloid by measuring the complex effective refractive index and the volume fraction occupied by the particles.

Engineering of refractive index in sulfide chalcogenide glass by direct laser writing

KAUST Repository

Zhang, Yaping

2010-01-01

Arsenic trisulfide (As2S3) glass is an interesting material for photonic integrated circuits (PICs) as infrared (IR) or nonlinear optical components. In this paper, direct laser writing was applied to engineer the refractive index of As2S3 thin film. Film samples were exposed to focused above bandgap light with wavelength at 405 nm using different fluence adjusted by laser power and exposure time. The index of refraction before and after laser irradiation was calculated by fitting the experimental data obtained from Spectroscopic Ellipsometer (SE) measurement to Tauc-Lorenz dispersion formula. A positive change in refractive index (Δn = 0.19 at 1.55 μm) as well as an enhancement in anisotropy was achieved in As2S3 film by using 10 mW, 0.3 μs laser irradiation. With further increasing the fluence, refractive index increased while anisotropic property weakened. Due to the rapid and large photo-induced modification of refractive index obtainable with high spatial resolution, this process is promising for integrated optic device fabrication.

Refractive index dispersion sensing using an array of photonic crystal resonant reflectors

DEFF Research Database (Denmark)

Hermannsson, Pétur Gordon; Vannahme, Christoph; Smith, Cameron

2015-01-01

Refractive index sensing plays a key role in various environmental and biological sensing applications. Here, a method is presented for measuring the absolute refractive index dispersion of liquids using an array of photonic crystal resonant reflectors of varying periods. It is shown that by cove......Refractive index sensing plays a key role in various environmental and biological sensing applications. Here, a method is presented for measuring the absolute refractive index dispersion of liquids using an array of photonic crystal resonant reflectors of varying periods. It is shown...... that by covering the array with a sample liquid and measuring the resonance wavelength associated with transverse electric polarized quasi guided modes as a function of period, the refractive index dispersion of the liquid can be accurately obtained using an analytical expression. This method is compact, can...... perform measurements at arbitrary number of wavelengths, and requires only a minute sample volume. The ability to sense a material's dispersion profile offers an added dimension of information that may be of benefit to optofluidic lab-on-a-chip applications. © 2015 AIP Publishing LLC....

Method of determining effects of heat-induced irregular refractive index on an optical system.

Science.gov (United States)

Song, Xifa; Li, Lin; Huang, Yifan

2015-09-01

The effects of an irregular refractive index on optical performance are examined. A method was developed to express a lens's irregular refractive index distribution. An optical system and its mountings were modeled by a thermomechanical finite element (FE) program in the predicted operating temperature range, -45°C-50°C. FE outputs were elaborated using a MATLAB optimization routine; a nonlinear least squares algorithm was adopted to determine which gradient equation best fit each lens's refractive index distribution. The obtained gradient data were imported into Zemax for sequential ray-tracing analysis. The root mean square spot diameter, modulation transfer function, and diffraction ensquared energy were computed for an optical system under an irregular refractive index and under thermoelastic deformation. These properties are greatly reduced by the irregular refractive index effect, which is one-third to five-sevenths the size of the thermoelastic deformation effect. Thus, thermal analyses of optical systems should consider not only thermoelastic deformation but also refractive index irregularities caused by inhomogeneous temperature.

Options for refractive index and viscosity matching to study variable density flows

Science.gov (United States)

Clément, Simon A.; Guillemain, Anaïs; McCleney, Amy B.; Bardet, Philippe M.

2018-02-01

Variable density flows are often studied by mixing two miscible aqueous solutions of different densities. To perform optical diagnostics in such environments, the refractive index of the fluids must be matched, which can be achieved by carefully choosing the two solutes and the concentration of the solutions. To separate the effects of buoyancy forces and viscosity variations, it is desirable to match the viscosity of the two solutions in addition to their refractive index. In this manuscript, several pairs of index matched fluids are compared in terms of viscosity matching, monetary cost, and practical use. Two fluid pairs are studied in detail, with two aqueous solutions (binary solutions of water and a salt or alcohol) mixed into a ternary solution. In each case: an aqueous solution of isopropanol mixed with an aqueous solution of sodium chloride (NaCl) and an aqueous solution of glycerol mixed with an aqueous solution of sodium sulfate (Na_2SO_4). The first fluid pair allows reaching high-density differences at low cost, but brings a large difference in dynamic viscosity. The second allows matching dynamic viscosity and refractive index simultaneously, at reasonable cost. For each of these four solutes, the density, kinematic viscosity, and refractive index are measured versus concentration and temperature, as well as wavelength for the refractive index. To investigate non-linear effects when two index-matched, binary solutions are mixed, the ternary solutions formed are also analyzed. Results show that density and refractive index follow a linear variation with concentration. However, the viscosity of the isopropanol and NaCl pair deviates from the linear law and has to be considered. Empirical correlations and their coefficients are given to create index-matched fluids at a chosen temperature and wavelength. Finally, the effectiveness of the refractive index matching is illustrated with particle image velocimetry measurements performed for a buoyant jet in a

Comparison of wavefront aberrations under cycloplegic, scotopic and photopic conditions using WaveScan

Directory of Open Access Journals (Sweden)

Rong Fan

2012-04-01

Full Text Available PURPOSE: To evaluate the differences of wavefront aberrations under cycloplegic, scotopic and photopic conditions. METHODS: A total of 174 eyes of 105 patients were measured using the wavefront sensor (WaveScan® 3.62 under different pupil conditions: cycloplegic 8.58 ± 0.54 mm (6.4 mm - 9.5 mm, scotopic 7.53 ± 0.69 mm (5.7 mm - 9.1 mm and photopic 6.08 ± 1.14 mm (4.1 mm - 8.8 mm. The pupil diameter, standard Zernike coefficients, root mean square of higher-order aberrations and dominant aberrations were compared between cycloplegic and scotopic conditions, and between scotopic and photopic conditions. RESULTS: The pupil diameter was 7.53 ± 0.69 mm under the scotopic condition, which reached the requirement of about 6.5 mm optical zone design in the wavefront-guided surgery and prevented measurement error due to the pupil centroid shift caused by mydriatics. Pharmacological pupil dilation induced increase of standard Zernike coefficients Z3-3, Z4(0 and Z5-5. The higher-order aberrations, third-order aberration, fourth-order aberration, fifth-order aberration, sixth-order aberration, and spherical aberration increased statistically significantly, compared to the scotopic condition (P<0.010. When the scotopic condition shifted to the photopic condition, the standard Zernike coefficients Z4(0, Z4², Z6-4, Z6-2, Z6² decreased and all the higher-order aberrations decreased statistically significantly (P<0.010, demonstrating that accommodative miosis can significantly improve vision under the photopic condition. Under the three conditions, the vertical coma aberration appears the most frequently within the dominant aberrations without significant effect by pupil size variance, and the proportion of spherical aberrations decreased with the decrease of the pupil size. CONCLUSIONS: The wavefront aberrations are significantly different under cycloplegic, scotopic and photopic conditions. Using the wavefront sensor (VISX WaveScan to measure scotopic

Refractive index calculation for analysis of aqueous solutions of heavy water

International Nuclear Information System (INIS)

Azuaga, N.S.; Marques, A.R.; Djega-Mariadassou, G.

1978-01-01

Refractive index measurements are used for analysis of aqueous solutions of D 2 O, particularly in the intermediate concentration range. The accuracy of titration is around 0.4% of atomic deuterium. Assuming that nsub(HDO)=(nsub(H 2 O)+nsub(D 2 O))/2, and that the refractive index of an initial mixture H 2 O-D 2 O is, in this case, an additive property of the molecular species, the refractive index n(t) of the ternary mixture (H 2 O-D 2 O-HDO) can be expressed by a relation. Using these two equations, it becomes possible to calculate the various types of calibration curves versus n, in the whole range of concentrations. To build these composition - n(t) curves, the only necessary data are the refractive index measurements of pure H 2 O and D 2 O and the value of equilibrium constant of the reaction H 2 O+D 2 O reversible 2HDO at the proper temperature [fr

Single-shot measurement of nonlinear absorption and nonlinear refraction.

Science.gov (United States)

Jayabalan, J; Singh, Asha; Oak, Shrikant M

2006-06-01

A single-shot method for measurement of nonlinear optical absorption and refraction is described and analyzed. A spatial intensity variation of an elliptical Gaussian beam in conjugation with an array detector is the key element of this method. The advantages of this single-shot technique were demonstrated by measuring the two-photon absorption and free-carrier absorption in GaAs as well as the nonlinear refractive index of CS2 using a modified optical Kerr setup.

About the correctness of laser refractive surgery in children

Directory of Open Access Journals (Sweden)

V. V. Kurenkov

2016-01-01

Full Text Available Disturbances of refraction are one of the most urgent problems of pediatric ophthalmology. Late and incomplete correction of refractive errors leads to the development of amblyopia, disturbances of binocular vision, the appearance of strabismus. Such complications reduce the quality of life, drastically limit the choice of professional child. Pediatric Ophthalmology always face a choice: many drugs and technologies are not approved for use in pediatric patients, practitioners are forced to use their «off-label», but such situations require great care and strict medical indications. For example, refractive surgery has worked well in adults, but its use remains controversial in children for security reasons and unpredictable effects. Several authors have described the use of laser refractive surgery in children under the age of 18 years, but there are no results of a multicenter, controlled study evaluating the safety, efficacy, and especially long-term results. In all the studies, the calculation was performed on adult nomograms ablation, while not proved how they are accurate for children. Long-term results and data on the endothelial cell density, corneal curvature changes in catamnesis are presented no longer than two years. Despite the fact that currently there is insufficient information about the results of remote application keratorefractive laser surgery in children, and there are no indication system and contraindications, modern achievements in medicine should be used in pediatric patients, and our successful track record proves it clearly. Undoubtedly, the positive experience of the laser surgery use in a child with clouding of the cornea in the outcome of herpetic keratitis, which provided a positive result: high visual acuity, binocular vision and lack of infection relapses for 2 years, requires study, evidence multicenter studies, and possibly expansion of indications for refractive laser surgery.

REFLECTION AND REFRACTION, VOLUME 2.

Science.gov (United States)

KLAUS, DAVID J.; AND OTHERS

THIS VOLUME 2 OF A TWO-VOLUME SET PROVIDES AUTOINSTRUCTION IN PHYSICS. THE UNITS COVERED IN THIS VOLUME ARE (1) REFLECTION OF LIGHT, (2) PHOTOMETRY, (3) POLARIZATION, (4) REFRACTION OF LIGHT, (5) SNELL'S LAW, (6) LENSES, FOCUS, AND FOCAL POINTS, (7) IMAGE FORMATION, AND (8) ABERRATIONS, THE EYE, AND MAGNIFICATION. THE INTRODUCTION AND UNITS ON…

Compressive and Shear Wave Velocity Profiles using Seismic Refraction Technique

International Nuclear Information System (INIS)

Aziman, M; Hazreek, Z A M; Azhar, A T S; Haimi, D S

2016-01-01

Seismic refraction measurement is one of the geophysics exploration techniques to determine soil profile. Meanwhile, the borehole technique is an established way to identify the changes of soil layer based on number of blows penetrating the soil. Both techniques are commonly adopted for subsurface investigation. The seismic refraction test is a non-destructive and relatively fast assessment compared to borehole technique. The soil velocities of compressive wave and shear wave derived from the seismic refraction measurements can be directly utilised to calculate soil parameters such as soil modulus and Poisson’s ratio. This study investigates the seismic refraction techniques to obtain compressive and shear wave velocity profile. Using the vertical and horizontal geophones as well as vertical and horizontal strike directions of the transient seismic source, the propagation of compressive wave and shear wave can be examined, respectively. The study was conducted at Sejagung Sri Medan. The seismic velocity profile was obtained at a depth of 20 m. The velocity of the shear wave is about half of the velocity of the compression wave. The soil profiles of compressive and shear wave velocities were verified using the borehole data and showed good agreement with the borehole data. (paper)

Interactive Dynamic Volume Illumination with Refraction and Caustics.

Science.gov (United States)

Magnus, Jens G; Bruckner, Stefan

2018-01-01

In recent years, significant progress has been made in developing high-quality interactive methods for realistic volume illumination. However, refraction - despite being an important aspect of light propagation in participating media - has so far only received little attention. In this paper, we present a novel approach for refractive volume illumination including caustics capable of interactive frame rates. By interleaving light and viewing ray propagation, our technique avoids memory-intensive storage of illumination information and does not require any precomputation. It is fully dynamic and all parameters such as light position and transfer function can be modified interactively without a performance penalty.

On the refractive index of sodium iodide solutions for index matching in PIV

Science.gov (United States)

Bai, Kunlun; Katz, Joseph

2014-04-01

Refractive index matching has become a popular technique for facilitating applications of modern optical diagnostic techniques, such as particle image velocimetry, in complex systems. By matching the refractive index of solid boundaries with that of the liquid, unobstructed optical paths can be achieved for illumination and image acquisition. In this research note, we extend previously provided data for the refractive index of aqueous solutions of sodium iodide (NaI) for concentrations reaching the temperature-dependent solubility limit. Results are fitted onto a quadratic empirical expression relating the concentration to the refractive index. Temperature effects are also measured. The present range of indices, 1.333-1.51, covers that of typical transparent solids, from silicone elastomers to several recently introduced materials that could be manufactured using rapid prototyping. We also review briefly previous measurements of the refractive index, viscosity, and density of NaI solutions, as well as prior research that has utilized this fluid.

Refractive errors in Cameroonians diagnosed with complete oculocutaneous albinism

Directory of Open Access Journals (Sweden)

Eballé AO

2013-07-01

Full Text Available André Omgbwa Eballé1,3, Côme Ebana Mvogo2, Christelle Noche4, Marie Evodie Akono Zoua2, Andin Viola Dohvoma21Faculty of Medicine and Pharmaceutical Sciences, University of Douala, Douala, Cameroon, 2Faculty of Medicine and Biomedical Sciences, University of Yaoundé I, Yaoundé, Cameroon; 3Yaoundé Gynaeco-obstetric and Paediatric Hospital. Yaoundé, Cameroon; 4Faculty of Medicine, Université des Montagnes. Bangangté, CameroonBackground: Albinism causes significant eye morbidity and amblyopia in children. The aim of this study was to determine the refractive state in patients with complete oculocutaneous albinism who were treated at the Gynaeco-Obstetric and Paediatric Hospital, Yaoundé, Cameroon and evaluate its effect on vision.Methods: We carried out this retrospective study at the ophthalmology unit of our hospital. All oculocutaneous albino patients who were treated between March 1, 2003 and December 31, 2011 were included.Results: Thirty-five patients (70 eyes diagnosed with complete oculocutaneous albinism were enrolled. Myopic astigmatism was the most common refractive error (40%. Compared with myopic patients, those with myopic astigmatism and hypermetropic astigmatism were four and ten times less likely, respectively, to demonstrate significant improvement in distance visual acuity following optical correction.Conclusion: Managing refractive errors is an important way to reduce eye morbidity-associated low vision in oculocutaneous albino patients.Keywords: albinism, visual acuity, refraction, Cameroon

Refraction in exoplanet atmospheres: Photometric signatures, implications for transmission spectroscopy, and search in Kepler data

OpenAIRE

Alp, Dennis; Demory, Brice-Olivier

2017-01-01

Refraction deflects photons that pass through atmospheres, which affects transit light curves. Refraction thus provides an avenue to probe physical properties of exoplanet atmospheres and to constrain the presence of clouds and hazes. In addition, an effective surface can be imposed by refraction, thereby limiting the pressure levels probed by transmission spectroscopy. The main objective of the paper is to model the effects of refraction on photometric light curves for realistic planets and ...

ASSOCIATION BETWEEN REFRACTIVE ERRORS AND SENILE CATARACT IN RURAL AREA OF WESTERN MAHARASHTRA

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Chaudhari Sagar V, Shelke Sanjay T, BangalSurekha V, Bhandari Akshay J, Kulkarni Ameya A

2015-04-01

Full Text Available Purpose: To study the association between refractive errors and senile cataract in rural area of western MaharashtraMaterials & Methods: It is a prospective cross sectional study carried out on 420 eyes of 210 patients with senile cataract was included in the study. The age and sex of the patient, grade and the refractive status of the cataract of the eyes were recorded. The grade of the cataract was recorded by the LOCS III (Lens Opacities Classification System, version III. Refractive status was measured subjectively using retinoscope and refractive error for each eye was converted into spherical equivalent units. Results: The age variation in the study was between 60-85 years.The maximum number of patients was in the age group of 60-65 years.The spherical equivalent ranged between -3.0 D to +4.25D.45.95% of the study population had a spherical equivalent between -2 to -1.73.81 % of the study population had a myopic refraction.20% had a hypermetropic refraction. Percentage of patients with a score of nuclear opalescence and colour between 1.0-2.0 was 41.90%, between 2.1-3.0 was 26.67% and above 3.0 was 31.43%.Percentage of patients with a score of cortical cataract between 0.1-1.0 was 69.76% and with a grade between 2.1-3.0 was 26.91 %. Percentage of patients with a score of posterior subcapsular cataract between 0.1-1.0 was 53.57% and with a grade between 2.1-3.0 was 39.05%. Conclusion: The myopic refraction was associated with nuclear, cortical and posterior subcapsular cataract and this refractive error was stastically significant with nuclear, cortical and posterior subcapsular cataract.

Wave refraction and prediction of breaker parameters along the Kerala Coast, India

Digital Repository Service at National Institute of Oceanography (India)

Sajeev, R.; Chandramohan, P.; SanilKumar, V.

significantly from place to place due to wave refraction and shoaling. The covergence and divergence of wave energy induce non-uniform distribution of wave heights during the monsoon period. Ezhimala promontory causes waves to refract considerably along...

Confining light with negative refraction in checkerboard metamaterials and photonic crystals

International Nuclear Information System (INIS)

Ramakrishna, S. Anantha; Guenneau, S.; Enoch, S.; Tayeb, G.; Gralak, B.

2007-01-01

We present here a finite slab of triangular checkerboard of negative refractive index material that exhibits a form of extraordinary transmission. We show that such a checkerboard can be used to confine light and can act as an open resonator. Effectively even a single point of intersection between three triangular wedges of negative refractive index may act as a resonator that confines light in the limit when n tends toward -1. We find that the quality of the confinement improves by adding more triangular wedges around the initial point in a checkerboard fashion. The confinement effect is also demonstrated by using a photonic crystal that shows the negative refraction effect

Omnidirectional refractive devices for flexural waves based on graded phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Torrent, Daniel, E-mail: daniel.torrent@iemn.univ-lille1.fr; Pennec, Yan; Djafari-Rouhani, Bahram [Institut d' Electronique, de Microléctronique et de Nanotechnologie, UMR CNRS 8520, Université de Lille 1, 59655 Villeneuve d' Ascq (France)

2014-12-14

Different omnidirectional refractive devices for flexural waves in thin plates are proposed and numerically analyzed. Their realization is explained by means phononic crystal plates, where a previously developed homogenization theory is employed for the design of graded index refractive devices. These devices consist of a circular cluster of inclusions with a properly designed gradient in their radius. With this approach, the Luneburg and Maxwell lenses and a family of beam splitters for flexural waves are proposed and analyzed. Results show that these devices work properly in a broadband frequency region, being therefore an efficient approach for the design of refractive devices specially interesting for nano-scale applications.

DISCRIMINATING BETWEEN CLOUDY, HAZY, AND CLEAR SKY EXOPLANETS USING REFRACTION

Energy Technology Data Exchange (ETDEWEB)

Misra, Amit K.; Meadows, Victoria S. [Astronomy Department, University of Washington, Seattle, WA 98195 (United States)

2014-11-01

We propose a method to distinguish between cloudy, hazy, and clear sky (free of clouds and hazes) exoplanet atmospheres that could be applicable to upcoming large aperture space- and ground-based telescopes such as the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT). These facilities will be powerful tools for characterizing transiting exoplanets, but only after a considerable amount of telescope time is devoted to a single planet. A technique that could provide a relatively rapid means of identifying haze-free targets (which may be more valuable targets for characterization) could potentially increase the science return for these telescopes. Our proposed method utilizes broadband observations of refracted light in the out-of-transit spectrum. Light refracted through an exoplanet atmosphere can lead to an increase of flux prior to ingress and subsequent to egress. Because this light is transmitted at pressures greater than those for typical cloud and haze layers, the detection of refracted light could indicate a cloud- or haze-free atmosphere. A detection of refracted light could be accomplished in <10 hr for Jovian exoplanets with JWST and <5 hr for super-Earths/mini-Neptunes with E-ELT. We find that this technique is most effective for planets with equilibrium temperatures between 200 and 500 K, which may include potentially habitable planets. A detection of refracted light for a potentially habitable planet would strongly suggest the planet was free of a global cloud or haze layer, and therefore a promising candidate for follow-up observations.

DISCRIMINATING BETWEEN CLOUDY, HAZY, AND CLEAR SKY EXOPLANETS USING REFRACTION

International Nuclear Information System (INIS)

Misra, Amit K.; Meadows, Victoria S.

2014-01-01

We propose a method to distinguish between cloudy, hazy, and clear sky (free of clouds and hazes) exoplanet atmospheres that could be applicable to upcoming large aperture space- and ground-based telescopes such as the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT). These facilities will be powerful tools for characterizing transiting exoplanets, but only after a considerable amount of telescope time is devoted to a single planet. A technique that could provide a relatively rapid means of identifying haze-free targets (which may be more valuable targets for characterization) could potentially increase the science return for these telescopes. Our proposed method utilizes broadband observations of refracted light in the out-of-transit spectrum. Light refracted through an exoplanet atmosphere can lead to an increase of flux prior to ingress and subsequent to egress. Because this light is transmitted at pressures greater than those for typical cloud and haze layers, the detection of refracted light could indicate a cloud- or haze-free atmosphere. A detection of refracted light could be accomplished in <10 hr for Jovian exoplanets with JWST and <5 hr for super-Earths/mini-Neptunes with E-ELT. We find that this technique is most effective for planets with equilibrium temperatures between 200 and 500 K, which may include potentially habitable planets. A detection of refracted light for a potentially habitable planet would strongly suggest the planet was free of a global cloud or haze layer, and therefore a promising candidate for follow-up observations

Refractive index and viscosity: dual sensing with plastic fibre gratings

Science.gov (United States)

Ferreira, Ricardo; Bilro, Lúcia; Marques, Carlos; Oliveira, Ricardo; Nogueira, Rogério

2014-05-01

A refractive index and viscosity sensor based on FBGs in mPOF is reported for the first time. The refractive index was measured with a sensitivity of -10:98nm=RIU and a resolution of 1 - 10-4RIU. Viscosity measurements were performed with acousto-optic modulation, obtaining a sensitivity of -94:42%=mPa • s and a resolution of 0:06mPa • s.

Temperature independent refractive index measurement using a fiber Bragg grating on abrupt tapered tip

Science.gov (United States)

Gomes, André D.; Silveira, Beatriz; Warren-Smith, Stephen C.; Becker, Martin; Rothhardt, Manfred; Frazão, Orlando

2018-05-01

A fiber Bragg grating was inscribed in an abrupt fiber taper using a femtosecond laser and phase-mask interferometer. The abrupt taper transition allows to excite a broad range of guided modes with different effective refractive indices that are reflected at different wavelengths according to Bragg's law. The multimode-Bragg reflection expands over 30 nm in the telecom-C-band. This corresponds to a mode-field overlap of up to 30% outside of the fiber, making the device suitable for evanescent field sensing. Refractive index and temperature measurements are performed for different reflection peaks. Temperature independent refractive index measurements are achieved by considering the difference between the wavelength shifts of two measured reflection peaks. A minimum refractive index sensitivity of 16 ± 1 nm/RIU was obtained in a low refractive index regime (1.3475-1.3720) with low influence of temperature (-0.32 ± 0.06 pm/°C). The cross sensitivity for this structure is 2.0 × 10-5 RIU/°C. The potential for simultaneous measurement of refractive index and temperature is also studied.

Determination of temperature dependant viscosity values of lubricants via simultaneous measurements of refractive index

International Nuclear Information System (INIS)

Yaltkaya, S.

2005-01-01

Viscosity is one of the most important parameter in rheological and tribological properties of fluids. The objective of this study is to obtain the viscosity values from the simultaneous refractive-index measurements of lubricants, simply by dipping the fiber-optic probe into the oil to be measured. Due to the fact that these parameters are temperature dependent, within the interval under consideration, oil heated up steadily while measuring the viscosity and refractive index at the same time. The refractive index sensor, the digital viscometer and the thermometer were connected to a PC via an analog to digital converter and the values were acquired at the same time. The fiber optic refractive index sensor has been designed in our laboratory. By utilising Fresnel's fundamental reflection law, the intensity of reflected light from boundary surface (optic fiber core-motor oil) was measured at 660 nm wavelength and then refractive index of the oil was calculated. The derived refractive index values were converted viscosity values that acquired by using the calibration equation. The viscometer, used during the study, was the rotational Brookfield type

Photo refractive effect in an Azo-dye doped polymer

International Nuclear Information System (INIS)

Khoshsima, H.

1997-01-01

Photo refractive, todays, is the frontier of nonlinear optics. The higher nonlinear properties, the more photo refractive effect will appear. In this experimental study, applying the experimental arrangement for Degenerate Four Wave Minx ing, we got benefit of P.V.K base polymer made complex with T.N.F, that is basically charge carrier. D.M.N.P.A.A chromophore molecules are used to produce second order nonlinear optics effect. Under the best experimental condition, the measured diffraction efficiency was about 70%

Role of percent peripheral tissue ablated on refractive outcomes following hyperopic LASIK

Science.gov (United States)

Stapleton, Fiona; Versace, Patrick

2017-01-01

Objectives To determine the effect of hyperopic laser in situ keratomileusis (H-LASIK) on corneal integrity, by investigating relationships between proportionate corneal tissue ablated and refractive outcomes at 3 months. Methods 18 eyes of 18 subjects treated with H-LASIK by Technolas 217c Excimer Laser were included in the study. Orbscan II Topography System was used to determine corneal volume and pachymetry 3mm temporally (3T). The volume of corneal tissue ablated was determined from the laser nomogram. Univariate associations between age, treatment, corneal volume, overall proportion of tissue removed, proportion of tissue removed at 3T, residual bed thickness at 3T and refractive outcomes 3 months post-LASIK were examined and independent factors associated with refractive outcomes determined using linear regression models. Results At 3 months post-LASIK, the mean difference to expected refractive outcome was -0.20 ± 0.64 (Range -2.00 to +1.00). In univariate analysis, difference to expected refractive outcome was associated with proportion of tissue removed at 3T (PLASIK, may present as either over or under-corrected at 3 months. The proportion of tissue removed at 3T was the single significant determinant of this outcome, suggesting unexpected biomechanical alterations resulting in corneal steepening. Future hyperopic LASIK procedures could consider proportionate volume of corneal tissue removed at 3T in addition to laser nomograms to achieve improved refractive outcomes. PMID:28151939

Wave refraction and backward magnon-plasmon polaritons in left-handed antiferromagnet/semiconductor superlattices

International Nuclear Information System (INIS)

Tarkhanyan, R.H.; Niarchos, D.G.

2007-01-01

Characteristics of the bulk electromagnetic waves in teraHertz frequency region are examined in a left-handed superlattice (SL) which consists of alternating layers of nonmagnetic semiconductor and nonconducting antiferromagnetic materials. General problem on the sign of the refractive index for anisotropic media is considered. It is shown that the phase refraction index is always positive while the group refractive index can be negative when some general conditions are fulfilled. Effective permittivity and permeability tensors of the SL are derived for perpendicular and parallel orientation of the magnetic anisotropy axis with respect to the plane of the layers. Problem of anomalous refraction for transverse electric and transverse magnetic-type polarized waves is examined in such media. Analytical expressions for both the phase and group refractive indices are obtained for various propagated modes. It is shown that, in general, three different types of the refracted waves with different relative orientation of the phase and group velocity vectors are possible in left-handed media. Unusual peculiarities of the backward modes corresponding to the coupled magnon-plasmon polaritons are considered. It is shown, in particular, that the number of the backward modes depends on the free charge carrier's density in semiconductor layers, variation of which allows to create different frequency regions for the wave propagation

Refractive index engineering of high performance coupler for compact photonic integrated circuits

Science.gov (United States)

Liu, Lu; Zhou, Zhiping

2017-04-01

High performance couplers are highly desired in many applications, but the design is limited by nearly unchangeable material refractive index. To tackle this issue, refractive index engineering method is investigated, which can be realized by subwavelength grating. Subwavelength gratings are periodical structures with pitches small enough to locally synthesize the refractive index of photonic waveguides, which allows direct control of optical profile as well as easier fabrication process. This review provides an introduction to the basics of subwavelength structures and pay special attention to the design strategies of some representative examples of subwavelength grating devices, including: edge couplers, fiber-chip grating couplers, directional couplers and multimode interference couplers. Benefited from the subwavelength grating which can engineer the refractive index as well as birefringence and dispersion, these devices show better performance when compared to their conventional counterparts.

Prevalence of refractive errors in the Slovak population calculated using the Gullstrand schematic eye model.

Science.gov (United States)

Popov, I; Valašková, J; Štefaničková, J; Krásnik, V

2017-01-01

A substantial part of the population suffers from some kind of refractive errors. It is envisaged that their prevalence may change with the development of society. The aim of this study is to determine the prevalence of refractive errors using calculations based on the Gullstrand schematic eye model. We used the Gullstrand schematic eye model to calculate refraction retrospectively. Refraction was presented as the need for glasses correction at a vertex distance of 12 mm. The necessary data was obtained using the optical biometer Lenstar LS900. Data which could not be obtained due to the limitations of the device was substituted by theoretical data from the Gullstrand schematic eye model. Only analyses from the right eyes were presented. The data was interpreted using descriptive statistics, Pearson correlation and t-test. The statistical tests were conducted at a level of significance of 5%. Our sample included 1663 patients (665 male, 998 female) within the age range of 19 to 96 years. Average age was 70.8 ± 9.53 years. Average refraction of the eye was 2.73 ± 2.13D (males 2.49 ± 2.34, females 2.90 ± 2.76). The mean absolute error from emmetropia was 3.01 ± 1.58 (males 2.83 ± 2.95, females 3.25 ± 3.35). 89.06% of the sample was hyperopic, 6.61% was myopic and 4.33% emmetropic. We did not find any correlation between refraction and age. Females were more hyperopic than males. We did not find any statistically significant hypermetopic shift of refraction with age. According to our estimation, the calculations of refractive errors using the Gullstrand schematic eye model showed a significant hypermetropic shift of more than +2D. Our results could be used in future for comparing the prevalence of refractive errors using same methods we used.Key words: refractive errors, refraction, Gullstrand schematic eye model, population, emmetropia.

Uncladded sensing fiber for refractive index measurement

International Nuclear Information System (INIS)

Bhardwaj, V.; Gangwar, R. K.; Pathak, A. K.; Singh, V. K.

2016-01-01

The formation of chemically etched optical fiber for use in refractive index sensor is addressed. This presented design of a refractive index (RI) sensor is based on recording the power loss exhibited by radiation propagating through an etched multimode fiber (MMF) immersed in the liquid under study. The decreasing diameters of fibers are found to be strongly dependent on the temperature and etchant composition. This experiment was performed for different unclad etched fibers for same sensing length and the RI changes from 1.33 RIU to 1.38 RIU. When the multimode fiber (MMF) is etched for 12 hours the sensitivity of the sensor is approximately 204.25dBm/RIU, which is larger than without etched fiber having sensitivity 127.2dBm/RIU.

Uncladded sensing fiber for refractive index measurement

Science.gov (United States)

Bhardwaj, V.; Gangwar, R. K.; Pathak, A. K.; Singh, V. K.

2016-05-01

The formation of chemically etched optical fiber for use in refractive index sensor is addressed. This presented design of a refractive index (RI) sensor is based on recording the power loss exhibited by radiation propagating through an etched multimode fiber (MMF) immersed in the liquid under study. The decreasing diameters of fibers are found to be strongly dependent on the temperature and etchant composition. This experiment was performed for different unclad etched fibers for same sensing length and the RI changes from 1.33 RIU to 1.38 RIU. When the multimode fiber (MMF) is etched for 12 hours the sensitivity of the sensor is approximately 204.25dBm/RIU, which is larger than without etched fiber having sensitivity 127.2dBm/RIU.

Uncladded sensing fiber for refractive index measurement

Energy Technology Data Exchange (ETDEWEB)

Bhardwaj, V., E-mail: bhardwajphyism@gmail.com; Gangwar, R. K.; Pathak, A. K.; Singh, V. K. [Department of Applied Physics Indian School of Mines Dhanbad, Jharkhand (India)

2016-05-06

The formation of chemically etched optical fiber for use in refractive index sensor is addressed. This presented design of a refractive index (RI) sensor is based on recording the power loss exhibited by radiation propagating through an etched multimode fiber (MMF) immersed in the liquid under study. The decreasing diameters of fibers are found to be strongly dependent on the temperature and etchant composition. This experiment was performed for different unclad etched fibers for same sensing length and the RI changes from 1.33 RIU to 1.38 RIU. When the multimode fiber (MMF) is etched for 12 hours the sensitivity of the sensor is approximately 204.25dBm/RIU, which is larger than without etched fiber having sensitivity 127.2dBm/RIU.

Interferometric investigation and simulation of refractive index in glass matrixes containing nanoparticles of varying sizes

Energy Technology Data Exchange (ETDEWEB)

Feeney, Michael Gerard; Ince, Rabia; Yukselici, Mehmet Hikmet; Allahverdi, Cagdas

2011-07-01

The relationship between refractive index and nanoparticle radii of cadmium selenide (CdSe) nanoparticles embedded within glass matrixes was investigated experimentally and by simulations. A homemade automated Michelson interferometer arrangement employing a rotating table and a He-Ne laser source at a wavelength of 632.8 nm determined the refractive index versus nanoparticle radii of embedded cadmium selenide (CdSe) nanoparticles. The refractive index was found to decrease linearly with nanoparticle radius increase. However, one sample showed a step increase in refractive index; on spectroscopic analysis, it was found that its resonant wavelength matched that of the He-Ne source wavelength. The simulations showed that two conditions caused the step increase in refractive index: low plasma frequency and matched sample and source resonances. This simple interferometer setup defines a new method of determining the radii of nanoparticles embedded in substrates and enables refractive index tailoring by modification of exact annealing conditions.

Ultracompact Refractive Index Sensor Based on Surface-Plasmon-Polariton Interference

International Nuclear Information System (INIS)

Wang Chen; Chen Jian-Jun; Tang Wei-Hua; Xiao Jing-Hua

2012-01-01

Using an ultracompact groove-slit-groove (GSG) structure, a refractive index sensor with a broadband response is proposed and experimentally demonstrated. Due to the interference of surface plasmon polaritons (SPPs), the transmission spectra in the GSG structure exhibit oscillation behaviors in a broad bandwidth, and they are quite sensitive to the refractive index of the surroundings. Based on the principle, the characteristics of its refractive index sensing are demonstrated experimentally. In the experiment, the structure is illuminated with a bulk light source (not a tightly focused light source) from the back side. This decreases the difficulty of the experimental measurement and can protect strong light sources from damaging the detection samples. Meanwhile, the whole structure of the sensor can be made more ultracompact without considering the influence of the incident waves

Refractive index and density in F- and Cl-doped silica glasses

International Nuclear Information System (INIS)

Kakiuchida, Hiroshi; Shimodaira, Noriaki; Sekiya, Edson H.; Saito, Kazuya; Ikushima, Akira J.

2005-01-01

The refractive index and density of fluorine- and chlorine-doped silica glasses were measured as functions of fictive temperature. The halogen concentrations were observed to have a refractive index or density that is independent of the fictive temperature were found. This implies that these properties are not affected by any heat-treatment conditions

Surface refractive index of the eye lens determined with an optic fiber sensor

International Nuclear Information System (INIS)

Pierscionek, B.K.

1993-01-01

The use of a fiber optic sensor for measurement of refractive index on the surface of eye lenses is described. The technique makes use of the fact that the amount of light reflected at the interface of two media (Fresnel reflectance) depends on the refractive-index difference between them. The sample is probed with a single-mode fiber, and the refractive index is calculated from the proportion of light reflected at the probe--sample interface

Matching-index-of-refraction of transparent 3D printing models for flow visualization

International Nuclear Information System (INIS)

Song, Min Seop; Choi, Hae Yoon; Seong, Jee Hyun; Kim, Eung Soo

2015-01-01

Matching-index-of-refraction (MIR) has been used for obtaining high-quality flow visualization data for the fundamental nuclear thermal-hydraulic researches. By this method, distortions of the optical measurements such as PIV and LDV have been successfully minimized using various combinations of the model materials and the working fluids. This study investigated a novel 3D printing technology for manufacturing models and an oil-based working fluid for matching the refractive indices. Transparent test samples were fabricated by various rapid prototyping methods including selective layer sintering (SLS), stereolithography (SLA), and vacuum casting. As a result, the SLA direct 3D printing was evaluated to be the most suitable for flow visualization considering manufacturability, transparency, and refractive index. In order to match the refractive indices of the 3D printing models, a working fluid was developed based on the mixture of herb essential oils, which exhibit high refractive index, high transparency, high density, low viscosity, low toxicity, and low price. The refractive index and viscosity of the working fluid range 1.453–1.555 and 2.37–6.94 cP, respectively. In order to validate the MIR method, a simple test using a twisted prism made by the SLA technique and the oil mixture (anise and light mineral oil) was conducted. The experimental results show that the MIR can be successfully achieved at the refractive index of 1.51, and the proposed MIR method is expected to be widely used for flow visualization studies and CFD validation for the nuclear thermal-hydraulic researches

Matching-index-of-refraction of transparent 3D printing models for flow visualization

Energy Technology Data Exchange (ETDEWEB)

Song, Min Seop; Choi, Hae Yoon; Seong, Jee Hyun; Kim, Eung Soo, E-mail: kes7741@snu.ac.kr

2015-04-01

Matching-index-of-refraction (MIR) has been used for obtaining high-quality flow visualization data for the fundamental nuclear thermal-hydraulic researches. By this method, distortions of the optical measurements such as PIV and LDV have been successfully minimized using various combinations of the model materials and the working fluids. This study investigated a novel 3D printing technology for manufacturing models and an oil-based working fluid for matching the refractive indices. Transparent test samples were fabricated by various rapid prototyping methods including selective layer sintering (SLS), stereolithography (SLA), and vacuum casting. As a result, the SLA direct 3D printing was evaluated to be the most suitable for flow visualization considering manufacturability, transparency, and refractive index. In order to match the refractive indices of the 3D printing models, a working fluid was developed based on the mixture of herb essential oils, which exhibit high refractive index, high transparency, high density, low viscosity, low toxicity, and low price. The refractive index and viscosity of the working fluid range 1.453–1.555 and 2.37–6.94 cP, respectively. In order to validate the MIR method, a simple test using a twisted prism made by the SLA technique and the oil mixture (anise and light mineral oil) was conducted. The experimental results show that the MIR can be successfully achieved at the refractive index of 1.51, and the proposed MIR method is expected to be widely used for flow visualization studies and CFD validation for the nuclear thermal-hydraulic researches.

The Complex Refractive Index of Volcanic Ash Aerosol Retrieved From Spectral Mass Extinction

Science.gov (United States)

Reed, Benjamin E.; Peters, Daniel M.; McPheat, Robert; Grainger, R. G.

2018-01-01

The complex refractive indices of eight volcanic ash samples, chosen to have a representative range of SiO2 contents, were retrieved from simultaneous measurements of their spectral mass extinction coefficient and size distribution. The mass extinction coefficients, at 0.33-19 μm, were measured using two optical systems: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter; values for the effective radius of ash particles measured in this study varied from 0.574 to 1.16 μm. Verification retrievals on high-purity silica aerosol demonstrated that the Rayleigh continuous distribution of ellipsoids (CDEs) scattering model significantly outperformed Mie theory in retrieving the complex refractive index, when compared to literature values. Assuming the silica particles provided a good analogue of volcanic ash, the CDE scattering model was applied to retrieve the complex refractive index of the eight ash samples. The Lorentz formulation of the complex refractive index was used within the retrievals as a convenient way to ensure consistency with the Kramers-Kronig relation. The short-wavelength limit of the electric susceptibility was constrained by using independently measured reference values of the complex refractive index of the ash samples at a visible wavelength. The retrieved values of the complex refractive indices of the ash samples showed considerable variation, highlighting the importance of using accurate refractive index data in ash cloud radiative transfer models.

X-ray refractive index: A tool to determine the average composition in multilayer structures

International Nuclear Information System (INIS)

Miceli, P.F.; Neumann, D.A.; Zabel, H.

1986-01-01

We present a novel and simple method to determine the average composition of multilayers and superlattices by measuring the x-ray refractive index. Since these modulated structures exhibit Bragg reflections at small angles, by using a triple axis x-ray spectrometer we have accurately determined the peak shifts due to refraction in GaAs/Al/sub x/Ga/sub 1-x/As and Nb/Ta superlattices. Knowledge of the refractive index provides the average fractional composition of the periodic structure since the refractive index is a superposition of the refractive indices of the atomic constituents. We also present a critical discussion of the method and compare the values of the average fractional composition obtained in this manner to the values obtained from the lattice parameter change in the GaAs/Al/sub x/Ga/sub 1-x/As superlattices due to the Al

Average value of the shape and direction factor in the equation of refractive index

Science.gov (United States)

Zhang, Tao

2017-10-01

The theoretical calculation of the refractive indices is of great significance for the developments of new optical materials. The calculation method of refractive index, which was deduced from the electron-cloud-conductor model, contains the shape and direction factor 〈g〉. 〈g〉 affects the electromagnetic-induction energy absorbed by the electron clouds, thereby influencing the refractive indices. It is not yet known how to calculate 〈g〉 value of non-spherical electron clouds. In this paper, 〈g〉 value is derived by imaginatively dividing the electron cloud into numerous little volume elements and then regrouping them. This paper proves that 〈g〉 = 2/3 when molecules’ spatial orientations distribute randomly. The calculations of the refractive indices of several substances validate this equation. This result will help to promote the application of the calculation method of refractive index.

Nonlinear refraction at the absorption edge in InAs.

Science.gov (United States)

Poole, C D; Garmire, E

1984-08-01

The results of measurements of nonlinear refraction at the absorption edge in InAs between 68 and 90 K taken with an HF laser are compared with those of a band-gap resonant model in which the contribution of the light-hole band is included and found to account for more than 40% of the observed nonlinear refraction. A generalized expression for the nonlinear index is derived by using the complete Fermi-Dirac distribution function. Good agreement between theory and experiment is obtained, with no free parameters.

Broadband manipulation of refracted wavefronts by gradient acoustic metasurface with V-shape structure

Science.gov (United States)

Lan, Jun; Li, Yifeng; Liu, Xiaozhou

2017-12-01

We present a space folding acoustic metasurface with a V-shaped structure, which exhibits ultra-broadband and high efficiency transmission compared to previously investigated space folding metasurfaces. The proposal employs a gradient refractive index profile to redirect the refracted wave arbitrarily and an existence of air channels with direct sound propagation to improve impedance matching between the metasurface and the background medium. As expected from frequency-independent generalized Snell's law, the demonstrated acoustic metasurface can steer refracted wavefronts at will, including anomalous refraction, non-diffracting Bessel beam, sub-wavelength flat lens, and conversion of the propagating wave into the surface wave. The designed V-shape metasurface overcomes the limitation of narrowband, which may offer potential applications in medical ultrasound imaging and broadband acoustical devices.

Anomalous incident-angle and elliptical-polarization rotation of an elastically refracted P-wave

Science.gov (United States)

Fa, Lin; Fa, Yuxiao; Zhang, Yandong; Ding, Pengfei; Gong, Jiamin; Li, Guohui; Li, Lijun; Tang, Shaojie; Zhao, Meishan

2015-08-01

We report a newly discovered anomalous incident-angle of an elastically refracted P-wave, arising from a P-wave impinging on an interface between two VTI media with strong anisotropy. This anomalous incident-angle is found to be located in the post-critical incident-angle region corresponding to a refracted P-wave. Invoking Snell’s law for a refracted P-wave provides two distinctive solutions before and after the anomalous incident-angle. For an inhomogeneously refracted and elliptically polarized P-wave at the anomalous incident-angle, its rotational direction experiences an acute variation, from left-hand elliptical to right-hand elliptical polarization. The new findings provide us an enhanced understanding of acoustical-wave scattering and lead potentially to widespread and novel applications.

[Correction of refractive errors in patients with strabismus. Part I. Clinical problems associated with refraction, accommodation and convergence].

Science.gov (United States)

Tokarz-Sawińska, Ewa

2012-01-01

In Part I the problems associated with refraction, accommodation and convergence and their role in proper eye position/visual alignment of the eyes as well as convergent, divergent and vertical alignment of the eyes have been described.

Super-virtual refraction interferometry: Field data example over a colluvial wedge

KAUST Repository

Hanafy, Sherif M.; Alhagan, Ola; Al-Tawash, Feras

2011-01-01

The theory of super-virtual refraction interferometry was recently developed to enhance the signal-to-noise ratio (SNR) of far-offset traces in refraction surveys. This enhancement of SNR is proportional to N, and can be as high as N if an iterative procedure is used. Here N is the number of post-critical shot positions that coincides with the receiver locations. We now demonstrate the enhancement of SNR of the super-virtual refraction traces for seismic data collected over a normal fault in Saudi Arabia. Results show that both the SNR of the super-virtual data set and the number of reliable first-arrival-traveltime picks are significantly increased. © 2011 Society of Exploration Geophysicists.

Refractive Thinking Profile In Solving Mathematical Problem Reviewed from Students Math Capability

Science.gov (United States)

Maslukha, M.; Lukito, A.; Ekawati, R.

2018-01-01

Refraction is a mental activity experienced by a person to make a decision through reflective thinking and critical thinking. Differences in mathematical capability have an influence on the difference of student’s refractive thinking processes in solving math problems. This descriptive research aims to generate a picture of refractive thinking of students in solving mathematical problems in terms of students’ math skill. Subjects in this study consisted of three students, namely students with high, medium, and low math skills based on mathematics capability test. Data collection methods used are test-based methods and interviews. After collected data is analyzed through three stages that are, condensing and displaying data, data display, and drawing and verifying conclusion. Results showed refractive thinking profiles of three subjects is different. This difference occurs at the planning and execution stage of the problem. This difference is influenced by mathematical capability and experience of each subject.

The use of a conical lens to find the refractive index of liquids

International Nuclear Information System (INIS)

Anguiano-Morales, Marcelino; Salas Peimbert, Didia P; Trujillo-Schiaffino, Gerardo

2011-01-01

In this work, the basic idea is to determine the refractive index of liquids unknown using a conical lens. The measurement of the refractive index of liquids is an important work in engineering and science since is one of the most important optical parameter. The adulteration problem is increasing day by day; therefore it is necessary to implement new and simple devices for measure the refractive index of several materials. There is a great variety of interferometric methods that may be used for determining the refractive index. However, these methods either need sophisticated equipment or have low accuracy. Our system consists of a conical lens coupled to a cylindrical container with a liquid whose composition can be changed easily or adulterated. The diameter of the emergent beam of the container is associated to the specific index of refraction of each substance. Any adulteration of the liquid will be reflected in the diameter of the beam, which will be detected by a charge-coupled device (CCD). Our hypothesis is supported by developed mathematical calculations and numerical simulations.

Change in spatial coherence of light on refraction and on reflection.

Science.gov (United States)

Lahiri, Mayukh; Wolf, Emil

2013-06-01

A theory of refraction and reflection of partially coherent electromagnetic beams has been recently developed. In this paper, we apply it to study the change in spatial coherence caused by refraction and by reflection more fully. By considering a Gaussian Schell-model beam, we show that the change is, in general, dependent on the angle of incidence.

Refractive errors in patients attending a private hospital in Jos, Nigeria

African Journals Online (AJOL)

Six hundred one (20.7%) patients with distant VA which improved with refraction were considered for this analysis. Two hundred twenty one (36.8%) of patients with refractive error were visually impaired (VA <6/12-3/60). Blindness (<3/60 ‑ none perception of light) was seen in 91 (15.1%) of the patients, seven of whom were ...

Single-mode optical waveguides on native high-refractive-index substrates

Directory of Open Access Journals (Sweden)

Richard R. Grote

2016-10-01

Full Text Available High-refractive-index semiconductor optical waveguides form the basis for modern photonic integrated circuits (PICs. However, conventional methods for achieving optical confinement require a thick lower-refractive-index support layer that impedes large-scale co-integration with electronics and limits the materials on which PICs can be fabricated. To address this challenge, we present a general architecture for single-mode waveguides that confine light in a high-refractive-index material on a native substrate. The waveguide consists of a high-aspect-ratio fin of the guiding material surrounded by lower-refractive-index dielectrics and is compatible with standard top-down fabrication techniques. This letter describes a physically intuitive, semi-analytical, effective index model for designing fin waveguides, which is confirmed with fully vectorial numerical simulations. Design examples are presented for diamond and silicon at visible and telecommunications wavelengths, respectively, along with calculations of propagation loss due to bending, scattering, and substrate leakage. Potential methods of fabrication are also discussed. The proposed waveguide geometry allows PICs to be fabricated alongside silicon CMOS electronics on the same wafer, removes the need for heteroepitaxy in III-V PICs, and will enable wafer-scale photonic integration on emerging material platforms such as diamond and SiC.

Dirac directional emission in anisotropic zero refractive index photonic crystals.

Science.gov (United States)

He, Xin-Tao; Zhong, Yao-Nan; Zhou, You; Zhong, Zhi-Chao; Dong, Jian-Wen

2015-08-14

A certain class of photonic crystals with conical dispersion is known to behave as isotropic zero-refractive-index medium. However, the discrete building blocks in such photonic crystals are limited to construct multidirectional devices, even for high-symmetric photonic crystals. Here, we show multidirectional emission from low-symmetric photonic crystals with semi-Dirac dispersion at the zone center. We demonstrate that such low-symmetric photonic crystal can be considered as an effective anisotropic zero-refractive-index medium, as long as there is only one propagation mode near Dirac frequency. Four kinds of Dirac multidirectional emitters are achieved with the channel numbers of five, seven, eleven, and thirteen, respectively. Spatial power combination for such kind of Dirac directional emitter is also verified even when multiple sources are randomly placed in the anisotropic zero-refractive-index photonic crystal.

Strategies for the management and prevention of complications in refractive laser surgery

NARCIS (Netherlands)

F. Hafezi (Farhad)

2008-01-01

textabstractObjective. Reoperations after refractive surgery have increased in frequency during the past 10 years. The spectrum of the indications for repeat LASIK may have changed. Methods. All cases of reoperations after refractive surgery performed between May 1, 2004 and April 30, 2005 at the

Thermally stimulated nonlinear refraction in gelatin stabilized Cu-PVP nanocomposite thin films

Energy Technology Data Exchange (ETDEWEB)

Tamgadge, Y. S., E-mail: ystamgadge@gmail.com; Atkare, D. V. [Department of Physics, Mahatma Fule Arts, Commerce & SitaramjiChoudhari Science College, Warud, Dist. Amravati (MS), India-444906 (India); Pahurkar, V. G.; Muley, G. G., E-mail: gajananggm@yahoo.co.in [Department of Physics, SantGadge Baba Amravati University, Amravati (MS), India-444602 (India); Talwatkar, S. S. [Department of Physics, D K Marathe and N G Acharya College, Chembur, Mumbai (MS), India-440071 (India); Sunatkari, A. L. [Department of Physics, Siddharth College of Arts, Science and Commerce, Fort, Mumbai (MS), India-440001 (India)

2016-05-06

This article illustrates investigations on thermally stimulated third order nonlinear refraction of Cu-PVP nanocomposite thin films. Cu nanoparticles have been synthesized using chemical reduction method and thin films in PVP matrix have been obtained using spin coating technique. Thin films have been characterized by X-ray diffraction (XRD) and Ultraviolet-visible (UV-vis) spectroscopyfor structural and linear optical studies. Third order nonlinear refraction studies have been performed using closed aperture z-scan technique under continuous wave (CW) He-Ne laser. Cu-PVP nanocomposites are found to exhibit strong nonlinear refractive index stimulated by thermal lensing effect.

The variable refractive index correction algorithm based on a stereo light microscope

International Nuclear Information System (INIS)

Pei, W; Zhu, Y Y

2010-01-01

Refraction occurs at least twice on both the top and the bottom surfaces of the plastic plate covering the micro channel in a microfluidic chip. The refraction and the nonlinear model of a stereo light microscope (SLM) may severely affect measurement accuracy. In this paper, we study the correlation between optical paths of the SLM and present an algorithm to adjust the refractive index based on the SLM. Our algorithm quantizes the influence of cover plate and double optical paths on the measurement accuracy, and realizes non-destructive, non-contact and precise 3D measurement of a hyaloid and closed container

The refractive index in electron microscopy and the errors of its approximations

Energy Technology Data Exchange (ETDEWEB)

Lentzen, M.

2017-05-15

In numerical calculations for electron diffraction often a simplified form of the electron-optical refractive index, linear in the electric potential, is used. In recent years improved calculation schemes have been proposed, aiming at higher accuracy by including higher-order terms of the electric potential. These schemes start from the relativistically corrected Schrödinger equation, and use a second simplified form, now for the refractive index squared, being linear in the electric potential. The second and higher-order corrections thus determined have, however, a large error, compared to those derived from the relativistically correct refractive index. The impact of the two simplifications on electron diffraction calculations is assessed through numerical comparison of the refractive index at high-angle Coulomb scattering and of cross-sections for a wide range of scattering angles, kinetic energies, and atomic numbers. - Highlights: • The standard model for the refractive index in electron microscopy is investigated. • The error of the standard model is proportional to the electric potential squared. • Relativistically correct error terms are derived from the energy-momentum relation. • The errors are assessed for Coulomb scattering varying energy and atomic number. • Errors of scattering cross-sections are pronounced at large angles and attain 10%.

The refractive index in electron microscopy and the errors of its approximations

International Nuclear Information System (INIS)

Lentzen, M.

2017-01-01

In numerical calculations for electron diffraction often a simplified form of the electron-optical refractive index, linear in the electric potential, is used. In recent years improved calculation schemes have been proposed, aiming at higher accuracy by including higher-order terms of the electric potential. These schemes start from the relativistically corrected Schrödinger equation, and use a second simplified form, now for the refractive index squared, being linear in the electric potential. The second and higher-order corrections thus determined have, however, a large error, compared to those derived from the relativistically correct refractive index. The impact of the two simplifications on electron diffraction calculations is assessed through numerical comparison of the refractive index at high-angle Coulomb scattering and of cross-sections for a wide range of scattering angles, kinetic energies, and atomic numbers. - Highlights: • The standard model for the refractive index in electron microscopy is investigated. • The error of the standard model is proportional to the electric potential squared. • Relativistically correct error terms are derived from the energy-momentum relation. • The errors are assessed for Coulomb scattering varying energy and atomic number. • Errors of scattering cross-sections are pronounced at large angles and attain 10%.

MANAGEMENT OF RESIDUAL REFRACTIVE ERROR AFTER CATARACT PHACOEMULSIFICATION. PART 2. INTRAOCULAR APPROACHES

Directory of Open Access Journals (Sweden)

K. B. Pershin

2017-01-01

Full Text Available The review presents an  analysis  of the  literature  data  on  the  methods of surgical  correction of residual  refractive  error after cataract phacoemulsification. Keratorefractive and intraocular approaches are  considered in details.  A comparison of the  efficacy and  safet y  of different groups   of methods on  the  example  of comparative studies is given.  Historically earlier  keratorefractive methods (laser  vision correction with LASIK and  PRK techniques on intact  eyes,  LASIK after  implantation  of multifocal  IOLs and arcuate keratotomy  after  phaco  are  indicated  for  the  correction of astigmatic refractive  error and  a small  spherical refractive error. Intraocular methods, including the  replacement of the  IOL  and  «piggyback» IOLs implantation  are  used  to  correct a large spherical refractive error. The introduction  of new  technology, the  implantation  of light-adjustable  IOLs, will  expand  the  existing evidence  and provide greater predictabilit y and efficiency of the  method  of correction of residual  refractive error.

Regular shock refraction in planar ideal MHD

International Nuclear Information System (INIS)

Delmont, P; Keppens, R

2010-01-01

We study the classical problem of planar shock refraction at an oblique density discontinuity, separating two gases at rest, in planar ideal (magneto)hydrodynamics. In the hydrodynamical case, 3 signals arise and the interface becomes Richtmyer-Meshkov unstable due to vorticity deposition on the shocked contact. In the magnetohydrodynamical case, on the other hand, when the normal component of the magnetic field does not vanish, 5 signals will arise. The interface then typically remains stable, since the Rankine-Hugoniot jump conditions in ideal MHD do not allow for vorticity deposition on a contact discontinuity. We present an exact Riemann solver based solution strategy to describe the initial self similar refraction phase. Using grid-adaptive MHD simulations, we show that after reflection from the top wall, the interface remains stable.

Trends in refractive surgery at an academic center: 2007-2009

OpenAIRE

Kuo, Irene C

2011-01-01

Abstract Background The United States officially entered a recession in December 2007, and it officially exited the recession in December 2009, according to the National Bureau of Economic Research. Since the economy may affect not only the volume of excimer laser refractive surgery, but also the clinical characteristics of patients undergoing surgery, our goal was to compare the characteristics of patients completing excimer laser refractive surgery and the types of procedures performed in t...

Effects of light refraction on the accuracy of camera calibration and reconstruction in underwater motion analysis.

Science.gov (United States)

Kwon, Young-Hoo; Casebolt, Jeffrey B

2006-07-01

One of the most serious obstacles to accurate quantification of the underwater motion of a swimmer's body is image deformation caused by refraction. Refraction occurs at the water-air interface plane (glass) owing to the density difference. Camera calibration-reconstruction algorithms commonly used in aquatic research do not have the capability to correct this refraction-induced nonlinear image deformation and produce large reconstruction errors. The aim of this paper is to provide a thorough review of: the nature of the refraction-induced image deformation and its behaviour in underwater object-space plane reconstruction; the intrinsic shortcomings of the Direct Linear Transformation (DLT) method in underwater motion analysis; experimental conditions that interact with refraction; and alternative algorithms and strategies that can be used to improve the calibration-reconstruction accuracy. Although it is impossible to remove the refraction error completely in conventional camera calibration-reconstruction methods, it is possible to improve the accuracy to some extent by manipulating experimental conditions or calibration frame characteristics. Alternative algorithms, such as the localized DLT and the double-plane method are also available for error reduction. The ultimate solution for the refraction problem is to develop underwater camera calibration and reconstruction algorithms that have the capability to correct refraction.

Theory, design, and experimental verification of a reflectionless bianisotropic Huygens' metasurface for wide-angle refraction

Science.gov (United States)

Chen, Michael; Abdo-Sánchez, Elena; Epstein, Ariel; Eleftheriades, George V.

2018-03-01

Huygens' metasurfaces are electrically thin devices which allow arbitrary field transformations. Beam refraction is among the first demonstrations of realized metasurfaces. As previously shown for extreme-angle refraction, control over only the electric impedance and magnetic admittance of the Huygens' metasurface proved insufficient to produce the desired reflectionless field transformation. To maintain zero reflections for wide refraction angles, magnetoelectric coupling between the electric and magnetic response of the metasurface, leading to bianisotropy, can be introduced. In this paper, we report the theory, design, and experimental characterization of a reflectionless bianisotropic metasurface for extreme-angle refraction of a normally incident plane wave towards 71.8° at 20 GHz. The theory and design of three-layer asymmetric bianisotropic unit cells are discussed. The realized printed circuit board structure was tested via full-wave simulations as well as experimental characterization. To experimentally verify the prototype, two setups were used. A quasi-optical experiment was conducted to assess the specular reflections of the metasurface, while a far-field antenna measurement characterized its refraction nature. The measurements verify that the fabricated metasurface has negligible reflections and the majority of the scattered power is refracted to the desired Floquet mode. This provides an experimental demonstration of a reflectionless wide-angle refracting metasurface using a bianisotropic Huygens' metasurface at microwave frequencies.

Frequency comb calibrated frequency-sweeping interferometry for absolute group refractive index measurement of air.

Science.gov (United States)

Yang, Lijun; Wu, Xuejian; Wei, Haoyun; Li, Yan

2017-04-10

The absolute group refractive index of air at 194061.02 GHz is measured in real time using frequency-sweeping interferometry calibrated by an optical frequency comb. The group refractive index of air is calculated from the calibration peaks of the laser frequency variation and the interference signal of the two beams passing through the inner and outer regions of a vacuum cell when the frequency of a tunable external cavity diode laser is scanned. We continuously measure the refractive index of air for 2 h, which shows that the difference between measured results and Ciddor's equation is less than 9.6×10-8, and the standard deviation of that difference is 5.9×10-8. The relative uncertainty of the measured refractive index of air is estimated to be 8.6×10-8. The data update rate is 0.2 Hz, making it applicable under conditions in which air refractive index fluctuates fast.

Fiber optic refractive index sensor using optofluidic anti-resonant reflecting guidance

Science.gov (United States)

Gao, Ran; Lu, Danfeng; Cheng, Jin; Qi, Zhi-mei

2017-10-01

An optofluidic anti-resonant reflecting guidance has been proposed and experimental demonstrated for the measurement of liquid refractive index. Two micro-channels were fabricated for the delivery of the liquid sample in the hollow core photonic crystal fiber by using femtosecond laser micromachining, serving as an inlet and outlet. The refractive index can be detected by using the resonant condition of the Fabry-Perot resonator, which is interrogated through the wavelength shift and of the lossy dip in the transmission spectrum. The experimental results show that the sensitivity of up to 1328 nm/RIU is achieved for the refractive index in the range from 1.345 to 1.363 RIU, respectively. The proposed sensor appears to have potential applications of precise measurement in chemistry, medicine, and biology.

Broadband giant-refractive-index material based on mesoscopic space-filling curves

Science.gov (United States)

Chang, Taeyong; Kim, Jong Uk; Kang, Seung Kyu; Kim, Hyowook; Kim, Do Kyung; Lee, Yong-Hee; Shin, Jonghwa

2016-08-01

The refractive index is the fundamental property of all optical materials and dictates Snell's law, propagation speed, wavelength, diffraction, energy density, absorption and emission of light in materials. Experimentally realized broadband refractive indices remain 1,800 resulting from a mesoscopic crystal with a dielectric constant greater than three million. This gigantic enhancement effect originates from the space-filling curve concept from mathematics. The principle is inherently very broad band, the enhancement being nearly constant from zero up to the frequency of interest. This broadband giant-refractive-index medium promises not only enhanced resolution in imaging and raised fundamental absorption limits in solar energy devices, but also compact, power-efficient components for optical communication and increased performance in many other applications.

Origami with negative refractive index to generate super-lenses

International Nuclear Information System (INIS)

Guenneau, Fanny; Chakrabarti, Sangeeta; Guenneau, Sebastien; Ramakrishna, S Anantha

2014-01-01

Negative refractive index materials (NRIM) enable unique effects including superlenses with a high degree of sub-wavelength image resolution, a capability that stems from the ability of NRIM to support a host of surface plasmon states. Using a generalized lens theorem and the powerful tools of transformational optics, a variety of focusing configurations involving complementary positive and negative refractive index media can be generated. A paradigm of such complementary media are checkerboards that consist of alternating cells of positive and negative refractive index, and are associated with very singular electromagnetics. We present here a variety of multi-scale checkerboard lenses that we call origami lenses and investigate their electromagnetic properties both theoretically and computationally. Some of these meta-structures in the plane display thin bridges of complementary media, and this highly enhances their plasmonic response. We demonstrate the design of three-dimensional checkerboard meta-structures of complementary media using transformational optics to map the checkerboard onto three-dimensional corner lenses, the only restriction being that the corresponding unfolded structures in the plane are constrained by the four color-map theorem. (paper)

Spherical subjective refraction with a novel 3D virtual reality based system.

Science.gov (United States)

Pujol, Jaume; Ondategui-Parra, Juan Carlos; Badiella, Llorenç; Otero, Carles; Vilaseca, Meritxell; Aldaba, Mikel

To conduct a clinical validation of a virtual reality-based experimental system that is able to assess the spherical subjective refraction simplifying the methodology of ocular refraction. For the agreement assessment, spherical refraction measurements were obtained from 104 eyes of 52 subjects using three different methods: subjectively with the experimental prototype (Subj.E) and the classical subjective refraction (Subj.C); and objectively with the WAM-5500 autorefractor (WAM). To evaluate precision (intra- and inter-observer variability) of each refractive tool independently, 26 eyes were measured in four occasions. With regard to agreement, the mean difference (±SD) for the spherical equivalent (M) between the new experimental subjective method (Subj.E) and the classical subjective refraction (Subj.C) was -0.034D (±0.454D). The corresponding 95% Limits of Agreement (LoA) were (-0.856D, 0.924D). In relation to precision, intra-observer mean difference for the M component was 0.034±0.195D for the Subj.C, 0.015±0.177D for the WAM and 0.072±0.197D for the Subj.E. Inter-observer variability showed worse precision values, although still clinically valid (below 0.25D) in all instruments. The spherical equivalent obtained with the new experimental system was precise and in good agreement with the classical subjective routine. The algorithm implemented in this new system and its optical configuration has been shown to be a first valid step for spherical error correction in a semiautomated way. Copyright © 2016 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.

Heritability and familial aggregation of refractive error in the Old Order Amish.

Science.gov (United States)

Peet, Jon A; Cotch, Mary-Frances; Wojciechowski, Robert; Bailey-Wilson, Joan E; Stambolian, Dwight

2007-09-01

To determine the heritability of refractive error and familial aggregation of myopia and hyperopia in an elderly Old Order Amish (OOA) population. Nine hundred sixty-seven siblings (mean age, 64.2 years) in 269 families were recruited for the Amish Eye Study in the Lancaster County area of Pennsylvania. Refractive error was determined by noncycloplegic manifest refraction. Heritability of refractive error was estimated with multivariate linear regression as twice the residual sibling-sibling correlation after adjustment for age and gender. Logistic regression models were used to estimate the sibling recurrence odds ratio (OR(s)). Myopia and hyperopia were defined with five different thresholds. The age- and gender-adjusted heritability of refractive error was 70% (95% CI: 48%-92%) in the OOA. Age and gender-adjusted OR(s) and sibling recurrence risk (lambda(s)), with different thresholds defining myopia ranged from 3.03 (95% CI: 1.58-5.80) to 7.02 (95% CI: 3.41-14.46) and from 2.36 (95% CI: 1.65-3.19) to 5.61 (95% CI: 3.06-9.34). Age and gender-adjusted OR(s) and lambda(s) for different thresholds of hyperopia ranged from 2.31 (95% CI: 1.56-3.42) to 2.94 (95% CI: 2.04-4.22) and from 1.33 (95% CI: 1.22-1.43) to 1.85 (95% CI: 1.18-2.78), respectively. Women were significantly more likely than men to have hyperopia. There was no significant gender difference in the risk of myopia. In the OOA, refractive error is highly heritable. Hyperopia and myopia aggregate strongly in OOA families.

An empirical method to estimate bulk particulate refractive index for ocean satellite applications

Digital Repository Service at National Institute of Oceanography (India)

Suresh, T.; Desa, E.; Mascarenhas, A.A.M.Q.; Matondkar, S.G.P.; Naik, P.; Nayak, S.R.

An empirical method is presented here to estimates bulk particulate refractive index using the measured inherent and apparent optical properties from the various waters types of the Arabian Sea. The empirical model, where the bulk refractive index...

Suppression of Air Refractive Index Variations in High-Resolution Interferometry

Directory of Open Access Journals (Sweden)

Zdeněk Buchta

2011-08-01

Full Text Available The influence of the refractive index of air has proven to be a major problem on the road to improvement of the uncertainty in interferometric displacement measurements. We propose an approach with two counter-measuring interferometers acting as a combination of tracking refractometer and a displacement interferometer referencing the wavelength of the laser source to a mechanical standard made of a material with ultra-low thermal expansion. This technique combines length measurement within a specified range with measurement of the refractive index fluctuations in one axis. Errors caused by different position of the interferometer laser beam and air sensors are thus eliminated. The method has been experimentally tested in comparison with the indirect measurement of the refractive index of air in a thermal controlled environment. Over a 1 K temperature range an agreement on the level of 5 × 10−8 has been achieved.

Measurement of the Specific Refractivities of CF4 and C2F6

Science.gov (United States)

Burner, A. W.; Goad, W. K.

1977-01-01

In order to relate the measured fringe shift of an interferometer to density, the relation between density rho and refractive index n must be known. For gases where the refractive index is close to unity, this relation between density and refractive index is very closely approximated by (n - 1) = K rho where K is the specific refractivity, or the Gladstone-Dale constant. The specific refractivity, which is weakly dependent on wavelength and temperature, is readily available for a number of common test gases such as N2 and air. For more unique test gases such as CF4 and C2F6 for which refractive index data at optical wavelengths is not readily available, the constants can be estimated from the atomic refractivities of carbon and fluorine. In order to verify this estimation, a two-beam interferometer was used to experimentally determine the specific refractivities of CF4 and C2F6. This data was required for holographic interferometric measurements made at the Langley Hypersonic CF4 Tunnel. A Twyman-Green interferometer with a He-Ne laser light source of vacuum wavelength lambda equal to 633 nm was used to measure the constants. One beam of the two-beam interferometer passed through an optical cell of known inside length l which could be evacuated and slowly filled with the test gas to a density of 7.2 kg/cu m for CF4 or 5.7 kg/cu m for C2F6. If the refractive index (and hence density) is constant along the optical path through the cell, the fringe shift M and density change Delta rho are related M = 2Kl Delta rho/lambda for the double pass interferometer. Thus K can be determined by measuring the fringe shift as the density is changed. The output of a photodiode used to detect the fringe shift was recorded on a strip chart recorder. The rate of pressure increase of the test gas in the cell was controlled such that the fringes shifted at a rate of 0.5 to 1 fringe per sec. The pressure in the test cell was measured with a high accuracy quartz crystal pressure

Negative refractions by triangular lattice sonic crystals in partial band gaps

International Nuclear Information System (INIS)

Alagoz, S.; Sahin, A.; Alagoz, B. B.; Nur, S.

2015-01-01

This study numerically demonstrates the effects of partial band gaps on the negative refraction properties of sonic crystal. The partial band gap appearing at the second band edge leads to the efficient transmissions of scattered wave envelopes in the transverse directions inside triangular lattice sonic crystal, and therefore enhances the refraction property of sonic crystal. Numerical simulation results indicate a diagonal guidance of coupled scattered wave envelopes inside crystal structure at the partial band gap frequencies and then output waves are restored in the vicinity of the output interface of sonic crystal by combining phase coherent scattered waves according to Huygens’ principles. This mechanism leads to two operations for wavefront engineering: one is spatial wavefront shifting operation and the other is convex–concave wavefront inversion operation. The effects of this mechanism on the negative refraction and wave focalization are investigated by using the finite difference time domain (FDTD) simulations. This study contributes to a better understanding of negative refraction and wave focusing mechanisms at the band edge frequencies, and shows the applications of the slab corner beam splitting and SC-air multilayer acoustic system. (paper)

Light Refraction by Water as a Rationale for the Poggendorff Illusion.

Science.gov (United States)

Bozhevolnyi, Sergey I

2016-08-24

The Poggendorff illusion in its classical form of parallel lines interrupting a transversal is viewed from the perspective of being related to the everyday experience of observing the light refraction in water. It is argued that if one considers a transversal to be a light ray in air and the parallel lines to form an occluding strip of a medium with the refractive index being between that of air and water, then one should be able to account, both qualitatively and quantitatively, for most of the features associated with the Poggendorff illusion. Statistical treatment of the visual experiments conducted with seven participants, each analyzing 50 configurations having different intercepting angles and strip widths, resulted in the effective refractive index of the occluding strip N = 1.13 ± 0.15, which is sufficiently close to the average (between that of water and air) refractive index of ∼1.17. It is further argued that the same mechanism can also be employed to account for many variants of the Poggendorff illusion, including the corner-Poggendorff pattern, as well as for the Hering illusion. © The Author(s) 2016.

Nonintrusive measurement of the liquid refractive index by using properties of the cuvette wall.

Science.gov (United States)

Xu, Ming; Ren, Junpeng; Miao, Runcai; Zhang, Zongquan

2016-10-01

We present a method of nonintrusive measurement of the refractive index of a liquid in a glass cuvette, which uses some optical properties of the cuvette wall and the principle of total internal reflection. By coating a transmission-scattering paint layer on the outer surface of the cuvette, we transform an incident laser beam into a transmitted scattered light. When the transmitted scattered light reaches the interface between the container wall and the liquid inside, the light beams satisfying the condition of total internal reflection are reflected to the coating layer, automatically forming a circular dark pattern that is related to the refractive index of the liquid. Based on an analytic relation between the diameter of the circular dark pattern and the refractive index of the liquid, we devised a method of in situ nonintrusive refractive index measurement. We tested the effect of several parameters on the measuring accuracy and found that the optimal thickness of the transmission-scattering layer is in the range of 50-70 μm, and the aperture of the diaphragm should be in the range of 0.7-1.0 mm. We measured the refractive indices of ethanol, Coca Cola, and red wine, and achieved an accuracy of ±3×10-4  RIU (refractive index unit).

Development and characterization of high refractive index and high scattering acrylate polymer layers

Science.gov (United States)

Eiselt, Thomas; Gomard, Guillaume; Preinfalk, Jan; Gleißner, Uwe; Lemmer, Uli; Hanemann, Thomas

2016-11-01

In this work, we develop a wet-processable scattering layer exhibiting a high refractive index that can be used in organic light-emitting diodes for light outcoupling purposes. The composite layers contain an acrylate casting resin, benzylmethacrylate, and phenanthrene, which is employed to increase the refractive index. The mixtures are first rheologically characterized and then polymerized with heat and UV radiation. For the refractive index measurements, the polymerized samples require a planar surface without air bubbles. To produce flat samples, a special construction consisting of a glass plate, a teflon sheet, a silicone ring (PDMS mold), another teflon sheet, and another glass plate is developed. Glue clamps are used to hold the construction together. The refractive index of the samples can be increased from 1.565 to 1.585 at 20°C at a wavelength of 589 nm following the addition of 20 wt% phenanthrene. A master mixture with a high refractive index is taken for further experiments. Nanoscaled titanium dioxide is added and dispersed into the master mixture and then spin coated on a glass substrate. These layers are optically characterized. Most of the presented layers present the expected haze of over 50%.

Directly patternable high refractive index ferroelectric sol–gel resist

Energy Technology Data Exchange (ETDEWEB)

Garoli, D., E-mail: denis.garoli@iit.it [Istituto Italiano di Tecnologia, Via Morego 16, 16136 Genova (Italy); Della Giustina, G. [Industrial Engineering Department, University of Padova and INSTM, Via Marzolo 9, 35131 Padova (Italy)

2015-08-15

The development of a ferroelectric negative tone sol–gel resist for Ultraviolet (UV) and Electron Beam (EB) lithography is presented. A new system based on Lead Zirconate Titanate (PZT, with formula PbZr{sub 0.52}Ti{sub 0.48}O{sub 3}) was synthesized by sol–gel method. The lithographic performances were investigated and several structures spanning from the micron range down to less than 50 nm have been achieved by UV and EB lithography. The system interaction with UV light and Electron beam was thoroughly characterized by FT-IT spectroscopy. The exposed PZT was annealed at high temperatures in order to study the crystalline phase evolution, the optical constants values and stability of patterned structures. After exposure and annealing, the refractive index of the material can vary from 1.68 up to 2.33 (@400 nm), while the ferroelectric behaviour seems to be maintained after high temperature annealing. These results suggest a possible application of PZT resist not only as ferroelectric but also as nanopatternable high refractive index material. Moreover, direct nanopatterning by means of Focused Ion Beam (FIB) lithography was verified and the potentiality for the preparation of high aspect ratio hollow nanostructures will be presented. - Highlights: • A new formula directly patternable PZT high refractive index resist is presented. • The gel is sensitive to both UV and electron beam exposure. • The refractive index can vary from 1.68 up to 2.33 (@400 nm). • Direct nanopatterning by means of Focused Ion Beam (FIB) lithography was verified. • High aspect ratio hollow nanostructures will be presented.

Refractive index based measurements

DEFF Research Database (Denmark)

2014-01-01

In a method for performing a refractive index based measurement of a property of a fluid such as chemical composition or temperature by observing an apparent angular shift in an interference fringe pattern produced by back or forward scattering interferometry, ambiguities in the measurement caused...... by the apparent shift being consistent with one of a number of numerical possibilities for the real shift which differ by 2n are resolved by combining measurements performed on the same sample using light paths therethrough of differing lengths....

Risk assessment for ectasia after corneal refractive surgery.

Science.gov (United States)

Randleman, J Bradley; Woodward, Maria; Lynn, Michael J; Stulting, R Doyle

2008-01-01

To analyze the epidemiologic features of ectasia after excimer laser corneal refractive surgery, to identify risk factors for its development, and to devise a screening strategy to minimize its occurrence. Retrospective comparative and case-control study. All cases of ectasia after excimer laser corneal refractive surgery published in the English language with adequate information available through December 2005, unpublished cases seeking treatment at the authors' institution from 1998 through 2005, and a contemporaneous control group who underwent uneventful LASIK and experienced a normal postoperative course. Evaluation of preoperative characteristics, including patient age, gender, spherical equivalent refraction, pachymetry, and topographic patterns; perioperative characteristics, including type of surgery performed, flap thickness, ablation depth, and residual stromal bed (RSB) thickness; and postoperative characteristics including time to onset of ectasia. Development of postoperative corneal ectasia. There were 171 ectasia cases, including 158 published cases and 13 unpublished cases evaluated at the authors' institution. Ectasia occurred after LASIK in 164 cases (95.9%) and after photorefractive keratectomy (PRK) in 7 cases (4.1%). Compared with controls, more ectasia cases had abnormal preoperative topographies (35.7% vs. 0%; Pvs. 40.0 years; Pvs. -5.09 diopters; Pvs. 546.5 microm; Pvs. 317.3 microm; PLASIK that, if validated, represents a significant improvement over current screening strategies.

Dried fruit breadfruit slices by Refractive Window™ technique

Directory of Open Access Journals (Sweden)

Diego F. Tirado

2016-01-01

Full Text Available A large amount of products are dried due several reasons as preservation, weight reduction and improvement of stability. However, on the market are not offered low-cost and high quality products simultaneously. Although there are effective methods of dehydrating foods such as freeze drying, which preserves the flavor, color and vitamins, they are poor accessibility technologies. Therefore, alternative processes are required to be efficient and economical. The aim of this research was compare drying kinetics of sliced of breadfruit (Artocarpus communis using the technique of Refractive Window® (VR with the tray drying. To carry out this study, sliced of 1 and 2 mm thick were used. Refractive window drying was performed with the water bath temperature to 92 °C; and tray drying at 62 °C and an air velocity of 0.52 m/s. During the Refractive window drying technique, the moisture content reached the lower than tray drying levels. Similarly it happened with samples of 1 mm, which, having a smaller diameter reached lower moisture levels than samples 2 mm. The higher diffusivities were obtained during drying sliced VR 1 and 2 mm with coefficients of 6.13 and 3.90*10-9 m2/s respectively.

Conical refraction in a degenerated two-crystal cascade

International Nuclear Information System (INIS)

Peet, V

2016-01-01

When a collimated light beam is passed consequently along the optic axes of two identical biaxial crystals, the conical refraction produces in the focal image plane a specific light pattern consisting of a ring and a central spot. The ring is formed due to the additive action of two crystals, while the spot results from the reversed conical refraction in such a degenerated cascade arrangement. The relative intensity of these two components depends on the azimuth angle between the orientations of the crystals about the beam axis. It is shown that this dependence arises due to the interference of pairs of waves produced by conical refraction in two crystals. If a part of these waves is blocked by polarization selection of beam components, the dependence of the light pattern on the azimuth angle vanishes. In this case, the outgoing light profile consists of a ring and a central spot with fixed intensities so that the total beam power is divided equally between these two components. Depending on the applied polarization, the central spot appears either as a restored input beam or a charge-two optical vortex. The results of numerical simulations of the effect are in a very good agreement with the experimental observations. (paper)

Nonlinearity of the refractive index due to an excitonic molecule resonance state in CdS

International Nuclear Information System (INIS)

Baumert, R.; Broser, I.; Buschick, K.

1986-01-01

The authors report the observation of an intensity-dependent refractive-index nonlinearity in CdS due to a resonance state where an excitonic molecule is created by induced absorption of light. The refractive index n as a function of the incident laser photon energy E is measured directly by light refraction in thin crystal prisms. A renormalized dielectric function describes the measured n(E) spectra well. This strong refractive-index nonlinearity is well suited to produce an optical bistability and to further strengthen the evidence of CdS to be an important material for laser-induced dynamic gratings

Changes in refractive characteristics in Japanese children with Down syndrome.

Science.gov (United States)

Horio, Junna; Kaneko, Hiroki; Takayama, Kei; Tuzuki, Kinichi; Kakihara, Hiroko; Iwami, Miou; Kawase, Yoshikatsu; Tsunekawa, Taichi; Yamaguchi, Naoko; Nonobe, Norie; Terasaki, Hiroko

2018-03-01

To investigate the refractive characteristics of Japanese children with Down syndrome. Retrospective study. The clinical records of refractive errors and ocular manifestations in children with Down syndrome who visited the Aichi Children's Health and Medical Center between November 2001 and January 2016 were retrospectively reviewed. The children were divided into the 3 following groups depending on their age: group 1 (≤ 6 years), group 2 (7-12 years), and group 3 (13-19 years). The collection of refractive error data was performed only for the right eyes and only once for each child, when the children were last examined with their pupils dilated. The study included 416 children (224 boys, 192 girls; average age, 6.1 ± 4.1 years). Group 3 had significantly stronger myopia than did groups 1 and 2. The mean cylindrical power in all the children was - 2.1 ± 1.2 diopters (D), and cylindrical power ≤ - 1.0 D (stronger than - 1.0 D) was seen in 366 eyes (88%). No significant difference in cylindrical power was found among the 3 groups. The spherical equivalent refraction showed an age-dependent myopic shift. Given that the amount of astigmatism did not show age-dependent differences, the age-dependent myopic shift could be due mainly to the change in spherical power.

Measurement of wavelength-dependent refractive indices of liquid scintillation cocktails

International Nuclear Information System (INIS)

Kossert, Karsten

2013-01-01

Refractive indices of several commercial liquid scintillation cocktails were measured by means of an automatic critical-angle dispersion refractometer in the wavelength range from 404.7 nm to 706.5 nm. The results are needed for various applications. In particular, detailed Monte Carlo simulations of liquid scintillation counters that include the computation of optical light require these data. In addition, the refractive index is an important parameter for studies of micelle sizes by means of dynamic light scattering. In this work, the refractive indices were determined for Ultima Gold™, Ultima Gold™ F, Ultima Gold™ LLT, Ultima Gold™ AB, Hionic Fluor™, Permafluor ® E+, Mineral Oil Scintillator, Insta-Gel Plus, OptiPhase HiSafe 2, OptiPhase HiSafe 3, Ultima Gold™ XR, Insta-Gel Plus, AquaLight, MaxiLight and Ultima Gold™ MV at 16 °C, 18 °C, 20 °C and 22 °C. The carbon dioxide absorber Carbo-Sorb ® E was also analyzed. For some scintillators, various batches were compared and mixtures with water or nitromethane were studied. - Highlights: • Refractive indices of several liquid scintillation cocktails were measured. • The wavelengths cover a range from 404.7 nm to 706.5 nm. • Measurements were carried out at 16 °C, 18 °C, 20 °C and 22 °C. • For some cocktails, mixtures with water or nitromethane were studied

Interferometric measurement of refractive index modification in a single mode microfiber

Science.gov (United States)

Ahmed, Farid; Ahsani, Vahid; Jun, Martin B. G.

2017-02-01

Efficient and cost effective measurement of the refractive index profile in an optical fiber is a significant technical job to design and manufacture in-fiber photonic devices and communication systems. For instance, to design fiber gratings, it is required to estimate the refractive index modulation to be inscribed by the fabrication apparatus such as ultraviolet or infrared lasers. Mach-Zehnder interferometer (MZI) based quantification of refractive index change written in single mode microfiber by femtosecond laser radiation is presented in this study. The MZI is constructed by splicing a microfiber (core diameter: 3.75 μm, cladding diameter: 40 μm) between standard single mode fibers. To measure the RI inscribed by infrared femtosecond laser, 200 μm length of the core within the MZI was scanned with laser radiation. As the higher index was written within 200 μm length of the core, the transmission spectrum of the interferometer displayed a corresponding red shift. The observed spectral shift was used to calculate the amount of refractive index change inscribed by the femtosecond irradiation. For the MZI length of 3.25 mm, and spectral shift of 0.8 nm, the calculated refractive index was found to be 0.00022. The reported results display excellent agreement between theory and experimental findings. Demonstrated method provides simple yet very effective on-site measurement of index change in optical fibers. Since the MZI can be constructed in diverse fiber types, this technique offers flexibility to quantify index change in various optical fibers.

Determination of refractive indices of biconvex lenses by use of a Michelson interferometer.

Science.gov (United States)

Chhaniwal, Vani K; Anand, Arun; Narayanamurthy, C S

2006-06-10

Measurements of lens parameters such as focal length, radius of curvature, and refractive index are important. We describe a measurement method that utilizes a Michelson interferometer to determine parameters of thin, convex lenses. The real fringe system formed by a Michelson interferometer is used to determine the focal lengths and the radii of curvature of the lenses. The refractive index of the lens material is determined from the thin-lens formula. We were able to determine the refractive indices to an accuracy as great as 99.97%. A detailed theoretical and experimental analysis is given.

Simultaneous refractive index and thickness measurement with the transmission interferometric adsorption sensor

Energy Technology Data Exchange (ETDEWEB)

Sannomiya, Takumi; Voeroes, Janos [Laboratory of Biosensors and Bioelectronics, Department of Information Technology and Electrical Engineering, ETH Zurich, 8092, Zurich (Switzerland); Balmer, Tobias E [Materials Research Center, ETH Zurich, 8093, Zurich (Switzerland); Heuberger, Manfred, E-mail: sannomiya@biomed.ee.ethz.c, E-mail: tobias.balmer@mat.ethz.c, E-mail: manfred.heuberger@empa.c, E-mail: janos.voros@biomed.ee.ethz.c [Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, 8093, Zurich (Switzerland)

2010-10-13

Refractive index and thickness of the adlayer are determined simultaneously using the transmission interferometric adsorption sensor (TInAS). Optical biosensors, where both refractive index and thickness of a homogeneous adlayer (thus the adsorbed mass) are determined simultaneously, so-called model-free biosensors, are important tools to investigate the adsorbed mass of biomolecules with unknown conformation. Our proposed calculation method enables model-free biosensing from a single spectrum acquired by a simple TInAS setup, namely using information of peak/dip positions as well as peak/dip intensities. The feasibility of this method was experimentally tested by adsorbing polyelectrolyte multilayer as well as biomolecules. To validate the new method also for the more intricate heterogeneous adlayer, the apparent refractive index and thickness were assessed theoretically by simulating a selection of different adsorbate configurations with the multiple multipole program (MMP). We found that a lateral inhomogeneity of the adsorbate (e.g. islands or adsorbed colloids) results in correct thickness and in reduced refractive index averaged in proportion to their density while vertically inhomogeneous density caused more complex responses. However, the apparent mass was always correct. Measurement errors can lead to significant errors in the apparent refractive index, particularly when the adlayer is very thin (<5 nm). This model-free TInAS technique would be useful not only for the measurement of adsorbed mass but also for the conformational analysis of the adsorbed molecules.

Comparing Models GRM, Refraction Tomography and Neural Network to Analyze Shallow Landslide

Directory of Open Access Journals (Sweden)

Armstrong F. Sompotan

2011-11-01

Full Text Available Detailed investigations of landslides are essential to understand fundamental landslide mechanisms. Seismic refraction method has been proven as a useful geophysical tool for investigating shallow landslides. The objective of this study is to introduce a new workflow using neural network in analyzing seismic refraction data and to compare the result with some methods; that are general reciprocal method (GRM and refraction tomography. The GRM is effective when the velocity structure is relatively simple and refractors are gently dipping. Refraction tomography is capable of modeling the complex velocity structures of landslides. Neural network is found to be more potential in application especially in time consuming and complicated numerical methods. Neural network seem to have the ability to establish a relationship between an input and output space for mapping seismic velocity. Therefore, we made a preliminary attempt to evaluate the applicability of neural network to determine velocity and elevation of subsurface synthetic models corresponding to arrival times. The training and testing process of the neural network is successfully accomplished using the synthetic data. Furthermore, we evaluated the neural network using observed data. The result of the evaluation indicates that the neural network can compute velocity and elevation corresponding to arrival times. The similarity of those models shows the success of neural network as a new alternative in seismic refraction data interpretation.

Falls and Postural Control in Older Adults With Eye Refractive Errors

Directory of Open Access Journals (Sweden)

Afsun Nodehi-Moghadam

2016-04-01

Conclusion: Vision impairment of older adults due to refractive error is not associated with an increase in falls. Furthermore, TUG test results did not show balance disorders in these groups. Further research, such as assessment of postural control with advanced devices and considering other falling risk factors is also needed to identify the predictors of falls in older adults with eye refractive errors.

Prevalence and risk factors of undercorrected refractive errors among Singaporean Malay adults: the Singapore Malay Eye Study.

Science.gov (United States)

Rosman, Mohamad; Wong, Tien Y; Tay, Wan-Ting; Tong, Louis; Saw, Seang-Mei

2009-08-01

To describe the prevalence and the risk factors of undercorrected refractive error in an adult urban Malay population. This population-based, cross-sectional study was conducted in Singapore in 3280 Malay adults, aged 40 to 80 years. All individuals were examined at a centralized clinic and underwent standardized interviews and assessment of refractive errors and presenting and best corrected visual acuities. Distance presenting visual acuity was monocularly measured by using a logarithm of the minimum angle of resolution (logMAR) number chart at a distance of 4 m, with the participants wearing their "walk-in" optical corrections (spectacles or contact lenses), if any. Refraction was determined by subjective refraction by trained, certified study optometrists. Best corrected visual acuity was monocularly assessed and recorded in logMAR scores using the same test protocol as was used for presenting visual acuity. Undercorrected refractive error was defined as an improvement of at least 0.2 logMAR (2 lines equivalent) in the best corrected visual acuity compared with the presenting visual acuity in the better eye. The mean age of the subjects included in our study was 58 +/- 11 years, and 52% of the subjects were women. The prevalence rate of undercorrected refractive error among Singaporean Malay adults in our study (n = 3115) was 20.4% (age-standardized prevalence rate, 18.3%). More of the women had undercorrected refractive error than the men (21.8% vs. 18.8%, P = 0.04). Undercorrected refractive error was also more common in subjects older than 50 years than in subjects aged 40 to 49 years (22.6% vs. 14.3%, P Malay adults with refractive errors was higher than that of the Singaporean Chinese adults with refractive errors. Undercorrected refractive error is a significant cause of correctable visual impairment among Singaporean Malay adults, affecting one in five persons.

Anomalous refraction of light colors by a metamaterial prism.

Science.gov (United States)

Silveirinha, Mário G

2009-05-15

A prism of glass separates white light into its spectral components in such a manner that colors associated with shorter wavelengths are more refracted than the colors associated with longer wavelengths. Here, we demonstrate that this property is not universal, and that a lossless metamaterial prism with a suitable microstructure may enable a broadband regime of anomalous dispersion, where the spectral components of light are separated in an unconventional way, so that "violet light" is less refracted than "red light." This phenomenon is fundamentally different from conventional anomalous dispersion effects, which are invariably accompanied by significant loss and are typically very narrow band.

Refractive index in generalized superconductors with Born-Infeld electrodynamics

Science.gov (United States)

Cheng, Jun; Pan, Qiyuan; Yu, Hongwei; Jing, Jiliang

2018-03-01

We investigate, in the probe limit, the negative refraction in the generalized superconductors with the Born-Infeld electrodynamics. We observe that the system has a negative Depine-Lakhtakia index in the superconducting phase at small frequencies and the greater the Born-Infeld corrections the larger the range of frequencies or the range of temperatures for which the negative refraction occurs. Furthermore, we find that the tunable Born-Infeld parameter can be used to improve the propagation of light in the holographic setup. Our analysis indicates that the Born-Infeld electrodynamics plays an important role in determining the optical properties of the boundary theory.

All-angle negative refraction and active flat lensing of ultraviolet light.

Science.gov (United States)

Xu, Ting; Agrawal, Amit; Abashin, Maxim; Chau, Kenneth J; Lezec, Henri J

2013-05-23

Decades ago, Veselago predicted that a material with simultaneously negative electric and magnetic polarization responses would yield a 'left-handed' medium in which light propagates with opposite phase and energy velocities--a condition described by a negative refractive index. He proposed that a flat slab of left-handed material possessing an isotropic refractive index of -1 could act like an imaging lens in free space. Left-handed materials do not occur naturally, and it has only recently become possible to achieve a left-handed response using metamaterials, that is, electromagnetic structures engineered on subwavelength scales to elicit tailored polarization responses. So far, left-handed responses have typically been implemented using resonant metamaterials composed of periodic arrays of unit cells containing inductive-capacitive resonators and conductive wires. Negative refractive indices that are isotropic in two or three dimensions at microwave frequencies have been achieved in resonant metamaterials with centimetre-scale features. Scaling the left-handed response to higher frequencies, such as infrared or visible, has been done by shrinking critical dimensions to submicrometre scales by means of top-down nanofabrication. This miniaturization has, however, so far been achieved at the cost of reduced unit-cell symmetry, yielding a refractive index that is negative along only one axis. Moreover, lithographic scaling limits have so far precluded the fabrication of resonant metamaterials with left-handed responses at frequencies beyond the visible. Here we report the experimental implementation of a bulk metamaterial with a left-handed response to ultraviolet light. The structure, based on stacked plasmonic waveguides, yields an omnidirectional left-handed response for transverse magnetic polarization characterized by a negative refractive index. By engineering the structure to have a refractive index close to -1 over a broad angular range, we achieve Veselago

Reflection from a flat dielectric film with negative refractive index

OpenAIRE

Hillion, Pierre

2007-01-01

We analyse the reflection of a TM electromagnetic field first on a flat dielectric film and second on a Veselago film with negative refractive index, both films being deposited on a metallic substrat acting as a mirror. An incident harmonic plane wave generates inside a conventional dielectric film a refracted propagating wave and an evanescent wave that does not contribute to reflection on the metallic substrat so that part of the information conveyed by the incident field is lost. At the op...

Perfect antireflection via negative refraction

International Nuclear Information System (INIS)

Monzon, Juan J.; Barriuso, Alberto G.; Sanchez-Soto, Luis L.

2006-01-01

We suggest a geometrical framework to discuss the action of slabs of negatively refracting materials. We show that these slabs generate the same orbits as normal materials, but traced out in opposite directions. This property allows us to confirm that the action of any lossless multilayer can be optically canceled by putting it together with the multilayer constructed as the inverted mirror image, with ε and μ reversed in sign

Turbulent effective absorptivity and refractivity

International Nuclear Information System (INIS)

Rax, J.M.

1984-09-01

The problem of wave propagation in a turbulent magnetized plasma is investigated. Considering small scale, low frequency density fluctuations we solve the Maxwell equations and show that the eikonal approximation remains valid with an effective refractivity and an effective absorptivity taking into account the energy diffusion due to the turbulent motion. Then the result is applied to the problem of lower hybrid waves scattering by drift waves density fluctuations in tokamaks

What is refractive optical bistability

International Nuclear Information System (INIS)

Dzhehov, Tomislav

1993-01-01

The basic elements of the theory of refractive optical bistability, assuming mediums with linear absorption are given. Special attention is paid to bistable etalons of semiconductor materials an oxide glasses, since some of them are considered as promising components for optical bistability applications. The design optimization of such devices for minimum switching intensity is analyzed. Computer simulation of the transfer characteristic recording for two InSb etalons is presented. (author)

Refractive index modulation in LiNbO3: MgO slab through Lamb wave

Science.gov (United States)

Prakash, Suraj; Sharma, Gaurav; Yadav, Gulab Chand; Singh, Vivek

2018-05-01

Present theoretical analysis deals with inducing refractive index contrast in Y-Z LiNbO3:MgO plate via GHz Lamb wave perturbation for photonic applications. Dispersion curves for Lamb wave in plate are plotted by employing displacement potential technique. Selecting wave parameters from dispersion curve, fundamental symmetric Lamb mode (S0) is excited in slab for 6GHz frequency. Produced displacement field by propagating S0 mode and thus developed strain is estimated to calculate refractive index modulation by applying photo-elastic relations. Modulated refractive index is of sinusoidal nature with period of modulation dependence on Lamb's wavelength. This plate having periodically modulated refractive index can be used as photonic crystal for different applications with acoustically tunable photonic band gap.

Direct Electrospray Printing of Gradient Refractive Index Chalcogenide Glass Films.

Science.gov (United States)

Novak, Spencer; Lin, Pao Tai; Li, Cheng; Lumdee, Chatdanai; Hu, Juejun; Agarwal, Anuradha; Kik, Pieter G; Deng, Weiwei; Richardson, Kathleen

2017-08-16

A spatially varying effective refractive index gradient using chalcogenide glass layers is printed on a silicon wafer using an optimized electrospray (ES) deposition process. Using solution-derived glass precursors, IR-transparent Ge 23 Sb 7 S 70 and As 40 S 60 glass films of programmed thickness are fabricated to yield a bilayer structure, resulting in an effective gradient refractive index (GRIN) film. Optical and compositional analysis tools confirm the optical and physical nature of the gradient in the resulting high-optical-quality films, demonstrating the power of direct printing of multimaterial structures compatible with planar photonic fabrication protocols. The potential application of such tailorable materials and structures as they relate to the enhancement of sensitivity in chalcogenide glass based planar chemical sensor device design is presented. This method, applicable to a broad cross section of glass compositions, shows promise in directly depositing GRIN films with tunable refractive index profiles for bulk and planar optical components and devices.

Anomalous Refraction of Acoustic Guided Waves in Solids with Geometrically Tapered Metasurfaces.

Science.gov (United States)

Zhu, Hongfei; Semperlotti, Fabio

2016-07-15

The concept of a metasurface opens new exciting directions to engineer the refraction properties in both optical and acoustic media. Metasurfaces are typically designed by assembling arrays of subwavelength anisotropic scatterers able to mold incoming wave fronts in rather unconventional ways. The concept of a metasurface was pioneered in photonics and later extended to acoustics while its application to the propagation of elastic waves in solids is still relatively unexplored. We investigate the design of acoustic metasurfaces to control elastic guided waves in thin-walled structural elements. These engineered discontinuities enable the anomalous refraction of guided wave modes according to the generalized Snell's law. The metasurfaces are made out of locally resonant toruslike tapers enabling an accurate phase shift of the incoming wave, which ultimately affects the refraction properties. We show that anomalous refraction can be achieved on transmitted antisymmetric modes (A_{0}) either when using a symmetric (S_{0}) or antisymmetric (A_{0}) incident wave, the former clearly involving mode conversion. The same metasurface design also allows achieving structure embedded planar focal lenses and phase masks for nonparaxial propagation.

Estimates of Atmospheric Distortion Number for Nonlinear Refraction

National Research Council Canada - National Science Library

Roadcap, J. R; McNicholl, P. J; Beland, R. R; Jumper, G. Y

2007-01-01

A characteristic nondimensional distortion number Nd was derived in the 1970s that allows inference of the degree of nonlinear refraction or thermal blooming associated with an atmospheric laser path...

Design of embedded system to determine liquid refractive index based on ultrasonic sensor using an ATMega328

Science.gov (United States)

Radiyonoa, Y.; Surantoro, S.; Pujayanto, P.; Budiharti, R.; Respati, Y. S.; Saputro, D. E.

2018-05-01

The occurrence of the broken pencil shadow into a glass of water becomes an interesting matter to be learned. The students of senior high school still find difficulty in determining liquid refractive index. To overcome this problem, it needs to develop an experimental tool to determine liquid refractive index by utilizing the newest technology. It is expected to be useful for students. This study is aimed to (1) make the design of physics learning experimental tool determinant of a liquid refractive index assisted by microcontroller based on ultrasonic sensors ATMega328 (2) explain the working principle and experimental result of liquid refractive indexing instrument assisted with ATMega328 microcontroller based ultrasonic sensor. This research used the experimental method. The result of the research shows design of physics learning experimental tool determinant of a liquid refractive index assisted by microcontroller based on ultrasonic sensors ATMega328 that has relative counting mistake of 0.36% on the measurement of aquades liquid refractive index, relative mistake of 0.18% on the 5% NaCl measurement, 0.24% on 5% glucose, and relative mistake of 0.50% on the measurement of 5 % fructose liquid refractive index. It has been created a proper device to be used in determining liquid refractive index.

Corneal polarimetry after LASIK refractive surgery

Science.gov (United States)

Bueno, Juan M.; Berrio, Esther; Artal, Pablo

2006-01-01

Imaging polarimetry provides spatially resolved information on the polarization properties of a system. In the case of the living human eye, polarization could be related to the corneal biomechanical properties, which vary from the normal state as a result of surgery or pathologies. We have used an aberro-polariscope, which we recently developed, to determine and to compare the spatially resolved maps of polarization parameters across the pupil between normal healthy and post-LASIK eyes. The depolarization distribution is not uniform across the pupil, with post-surgery eyes presenting larger levels of depolarization. While retardation increases along the radius in normal eyes, this pattern becomes irregular after LASIK refractive surgery. The maps of slow axis also differ in normal and post-surgery eyes, with a larger disorder in post-LASIK eyes. Since these changes in polarization indicate subtle structural modifications of the cornea, this approach can be useful in a clinical environment to follow the biomechanical and optical changes of the cornea after refractive surgery or for the early diagnosis of different corneal pathologies.

Method of determining dispersion dependence of refractive index of nanospheres building opals

Science.gov (United States)

Kępińska, Mirosława; Starczewska, Anna; Duka, Piotr

2017-11-01

The method of determining dispersion dependence of refractive index of nanospheres building opals is presented. In this method basing on angular dependences of the spectral positions of Bragg diffraction minima on transmission spectra for opal series of known spheres diameter, the spectrum of effective refractive index for opals and then refractive index for material building opal's spheres is determined. The described procedure is used for determination of neff(λ) for opals and nsph(λ) for material which spheres building investigated opals are made of. The obtained results are compared with literature data of nSiO2(λ) considered in the analysis and interpretation of extremes related to the light diffraction at (hkl) SiO2 opal planes.

Printable photonic crystals with high refractive index for applications in visible light

International Nuclear Information System (INIS)

Calafiore, Giuseppe; Mejia, Camilo A; Munechika, Keiko; Peroz, Christophe; Piña-Hernandez, Carlos; Fillot, Quentin; Dhuey, Scott; Sassolini, Simone; Salvadori, Filippo; Cabrini, Stefano

2016-01-01

Nanoimprint lithography (NIL) of functional high-refractive index materials has proved to be a powerful candidate for the inexpensive manufacturing of high-resolution photonic devices. In this paper, we demonstrate the fabrication of printable photonic crystals (PhCs) with high refractive index working in the visible wavelengths. The PhCs are replicated on a titanium dioxide-based high-refractive index hybrid material by reverse NIL with almost zero shrinkage and high-fidelity reproducibility between mold and printed devices. The optical responses of the imprinted PhCs compare very well with those fabricated by conventional nanofabrication methods. This study opens the road for a low-cost manufacturing of PhCs and other nanophotonic devices for applications in visible light. (paper)

Silicon photonic crystal nanostructures for refractive index sensing

DEFF Research Database (Denmark)

Dorfner, Dominic; Hürlimann, T.; Zabel, T.

2008-01-01

The authors present the fabrication and optical investigation of Silicon on Insulator photonic crystal drop-filters for use as refractive index sensors. Two types of defect nanocavities (L3 and H1-r) are embedded between two W1 photonic crystal waveguides to evanescently route light at the cavity...... mode frequency between input and output waveguides. Optical characterization of the structures in air and various liquids demonstrate detectivities in excess of n=n = 0:018 and n=n = 0:006 for the H1-r and L3 cavities, respectively. The measured cavity-frequencies and detector refractive index...... responsivities are in good agreement with simulations, demonstrating that the method provides a background free transducer signal with frequency selective addressing of a specic area of the sensor chip....

Characterising refractive index dispersion in chalcogenide glasses

DEFF Research Database (Denmark)

Fang, Y.; Sojka, L.; Jayasuriya, D.

2016-01-01

Much effort has been devoted to the study of glasses that contain the chalcogen elements (sulfur, selenium and tellurium) for photonics' applications out to MIR wavelengths. In this paper we describe some techniques for determining the refractive index dispersion characteristics of these glasses...

Wave refraction studies off Agonda beach (Goa)

Digital Repository Service at National Institute of Oceanography (India)

Krishnakumar, V.; Pathak, M.C.; Kotnala, K.L.

Analysis of wave refraction and longshore current has been carried out for a narrow strip off the shores of Agonda (Goa, India). Zones with high wave energy and rip currents have been demarcated. It is found from the analysis that the southern part...

High refractive index modification of SiO2 created by femtosecond laser nanostructuring

International Nuclear Information System (INIS)

Barillot, T; Grojo, D; Gertsvolf, M; Rayner, D M; Corkum, P B; Lei, S

2010-01-01

By comparing simulations with experiment, we show that the effective refractive index of fused SiO 2 can be locally reduced by (1.8 ± 0.2)% by femtosecond laser nanostructuring. We create a microlens of material containing a planar array of nanocracks embedded inside fused silica and probe how it refracts or absorbs light as a function of pulse energy. The self-generated microlens lowers the peak light intensity by deflecting the light around the focus. We obtain the refractive index by simulating the beam transport using the 3D wave equation in conjunction with the measured dimensions of the modified material.

Effects of Atmospheric Refraction on an Airborne Weather Radar Detection and Correction Method

Directory of Open Access Journals (Sweden)

Lei Wang

2015-01-01

Full Text Available This study investigates the effect of atmospheric refraction, affected by temperature, atmospheric pressure, and humidity, on airborne weather radar beam paths. Using three types of typical atmospheric background sounding data, we established a simulation model for an actual transmission path and a fitted correction path of an airborne weather radar beam during airplane take-offs and landings based on initial flight parameters and X-band airborne phased-array weather radar parameters. Errors in an ideal electromagnetic beam propagation path are much greater than those of a fitted path when atmospheric refraction is not considered. The rates of change in the atmospheric refraction index differ with weather conditions and the radar detection angles differ during airplane take-off and landing. Therefore, the airborne radar detection path must be revised in real time according to the specific sounding data and flight parameters. However, an error analysis indicates that a direct linear-fitting method produces significant errors in a negatively refractive atmosphere; a piecewise-fitting method can be adopted to revise the paths according to the actual atmospheric structure. This study provides researchers and practitioners in the aeronautics and astronautics field with updated information regarding the effect of atmospheric refraction on airborne weather radar detection and correction methods.

The relationship between refractive and biometric changes during Edinger–Westphal stimulated accommodation in rhesus monkeys

Science.gov (United States)

Vilupuru, Abhiram S.; Glasser, Adrian

2010-01-01

Experiments were undertaken to understand the relationship between dynamic accommodative refractive and biometric (lens thickness (LT), anterior chamber depth (ACD) and anterior segment length (ASL=ACD+LT)) changes during Edinger–Westphal stimulated accommodation in rhesus monkeys. Experiments were conducted on three rhesus monkeys (aged 11·5, 4·75 and 4·75 years) which had undergone prior, bilateral, complete iridectomies and implantation of a stimulating electrode in the Edinger–Westphal (EW) nucleus. Accommodative refractive responses were first measured dynamically with video-based infrared photorefraction and then ocular biometric responses were measured dynamically with continuous ultrasound biometry (CUB) during EW stimulation. The same stimulus amplitudes were used for the refractive and biometric measurements to allow them to be compared. Main sequence relationships (ratio of peak velocity to amplitude) were calculated. Dynamic accommodative refractive changes are linearly correlated with the biometric changes and accommodative biometric changes in ACD, ASL and LT show systematic linear correlations with increasing accommodative amplitudes. The relationships are relatively similar for the eyes of the different monkeys. Dynamic analysis showed that main sequence relationships for both biometry and refraction are linear. Although accommodative refractive changes in the eye occur primarily due to changes in lens surface curvature, the refractive changes are well correlated with A-scan measured accommodative biometric changes. Accommodative changes in ACD, LT and ASL are all well correlated over the full extent of the accommodative response. PMID:15721617

Computed estimation of visual acuity after laser refractive keratectomy

Science.gov (United States)

Rol, Pascal O.; Parel, Jean-Marie A.; Hanna, Khalil

1991-06-01

A number of surgical techniques has been developed to correct ametropia (refractive defaults) of the eye by changing the anterior corneal radius. Because the air-cornea interface makes up for about two-third of the refractive power of the eye, a refractive correction is obtained by a suitable photoablation of the cornea. For this purpose, e.g., an ArF excimer laser which emits a wavelength of 193 nm is being used. After a mechanical removal of the epithelium, the Bowman's layer and the corneal stroma are photoablated on typically 50% of the central surface of the cornea with various precomputed shapes. Methods using a variable diaphragm1 or a scanning slit2 are being utilized. After regrowth of the epithelium, a smooth interface with air develops itself, which can be attributed to a mechanical equilibration. Yet, SEM studies have shown that with such kind of treatments, irregularities can remain in the new stromal surface (Fig. 1). A possible explanation for this effect is associated with an inhomogeneous energy distribution of the laser beam profile3. To some extent, the stromal surface is equalized by the epithelial layer during healing& However, as the corneal epithelium and stroma have different refractive indices, a scatter of the incident light may result causing a haze in the cornea and a blur of the image at the retina. In such a case the resolution and the contrast performance of the eye which is expected from a successful operation, may be reduced. This study is an attempt to quantify the vision blur as a function of the deformation observed at the epithelium-stroma interface.

A new iterative algorithm to reconstruct the refractive index.

Science.gov (United States)

Liu, Y J; Zhu, P P; Chen, B; Wang, J Y; Yuan, Q X; Huang, W X; Shu, H; Li, E R; Liu, X S; Zhang, K; Ming, H; Wu, Z Y

2007-06-21

The latest developments in x-ray imaging are associated with techniques based on the phase contrast. However, the image reconstruction procedures demand significant improvements of the traditional methods, and/or new algorithms have to be introduced to take advantage of the high contrast and sensitivity of the new experimental techniques. In this letter, an improved iterative reconstruction algorithm based on the maximum likelihood expectation maximization technique is presented and discussed in order to reconstruct the distribution of the refractive index from data collected by an analyzer-based imaging setup. The technique considered probes the partial derivative of the refractive index with respect to an axis lying in the meridional plane and perpendicular to the propagation direction. Computer simulations confirm the reliability of the proposed algorithm. In addition, the comparison between an analytical reconstruction algorithm and the iterative method has been also discussed together with the convergent characteristic of this latter algorithm. Finally, we will show how the proposed algorithm may be applied to reconstruct the distribution of the refractive index of an epoxy cylinder containing small air bubbles of about 300 micro of diameter.

Towards a Negative Refractive Index in an Atomic System

Science.gov (United States)

Simmons, Zach; Brewer, Nick; Yavuz, Deniz

2014-05-01

The goal of our experiments is to obtain a negative index of refraction in the optical region of the spectrum using an atomic system. The concept of negative refraction, which was first predicted by Veselago more than four decades ago, has recently emerged as a very exciting field of science. Negative index materials exhibit many seemingly strange properties such as electromagnetic vectors forming a left-handed triad. A key potential application for these materials was discovered in 2000 when Pendry predicted that a slab with a negative refractive index can image objects with a resolution far better than the diffraction limit. Thus far, research in negative index materials has primarily focused on meta-materials. The fixed response and often large absorption of these engineered materials motivates our efforts to work in an atomic system. An atomic media offers the potential to be actively modified, for example by changing laser parameters, and can be tuned to cancel absorption. A doped crystal allows for high atomic densities compared to other atomic systems. So far we have identified a transition in such a material, Eu:YSO, as a candidate for these experiments and are performing spectroscopy on this material.

Comment on "Total Negative Refraction in Real Crystals for Ballistic Electrons and Light" (Phys. Rev. Lett. 91, 157404 (2003))

OpenAIRE

Yau, H. -F.; Liu, J. -P.; Ke, B.; Kuo, C. -H.; Ye, Z.

2003-01-01

Recently, Zhang et al. (Phys. Rev. Lett. 91, 157404 (2003)) have demonstrated that an amphoteric refraction, i. e. both positive and negative refraction, may prevail at the interface of two uniaxial anisotropic crystals when their optical axes are in different directions. The authors subsequently made a correspondence between such a refraction with the negative refraction expected for Left Handed Materials (LHMs). Here we comment that the amphoteric refraction can be observed even with one un...

Refraction angle and edge visibility in X-ray diffraction enhanced imaging

International Nuclear Information System (INIS)

Chen Yu; Jia Quanjie; Li Gang; Wang Yuzhu; Xue Xianying; Jiang Xiaoming

2007-01-01

Diffraction-enhanced X-ray imaging could extract accurately the refraction angles of the sample, which is very important to increase the image contrast of low Z samples. In this paper, the DEI experiments with X-rays of different energies were performed both on wedge-shaped and rounded model samples. Refraction angles of the two samples were all obtained accurately, and the results agreed well with the calculations. Quantitative analyses based on Edge Visibility were performed for the wedge-shaped model sample. The results revealed that the calculated positions for the Best Edge Visibility of the slope with fixed refraction angle were calculable in good agreement with the experimental results. A quantitative research on the Edge Visibility of real tissues sample was carried out and the optimal condition for best contrast of DEI images were discussed. (authors)

Cover-layer with High Refractive Index for Near-Field Recording Media

Science.gov (United States)

Kim, Jin-Hong; Lee, Jun-Seok

2007-06-01

TiO2 nanoparticles are added into UV-curable resin to increase the refractive index of the cover-layer laminated for cover-layer incident near-field recording media. A high refractive index is required for the cover-layer operating with an optical head with a high numerical aperture. The eye pattern from a cover-layer coated 20 GB read-only memory disc in which the refractive index of the cover-layer is 1.75 is achieved, but the gap servo is unstable owing to the rough surface of the cover-layer. Even though the light loss due to the nanoparticles is negligible, a rough microstructure is developed by adding the nanoparticles into an organic binder material. To achieve a smooth surface for a stable gap servo, the solubility of the nanoparticles should be enhanced by the optimization of the surface of the nanoparticles.

Photochromic Polyurethanes Showing a Strong Change of Transparency and Refractive Index

Directory of Open Access Journals (Sweden)

Luca Oggioni

2017-09-01

Full Text Available Photochromic polymers have been studied as rewritable systems for optical elements with tunable transparency in the visible and refractive index in the NIR. Six diarylethene monomers have been synthesized to give thin films of photochromic polyurethanes. The absorption properties of the monomers in solution and of the corresponding polymeric films have been evaluated showing that a transparency contrast in the visible spectrum of the order of 10 3 can be obtained by a suitable choice of the chemical structure and illumination wavelength. The change in the refractive index in the NIR have been determined by ellipsometry showing changes larger than 10 − 2 . A trend of this variation with the absorption properties has been also highlighted. Fresnel lenses working on the basis of both a change of the transparency and the refractive index (amplitude and phase have been demonstrated.

Magnetic compound refractive lens for focusing and polarizing cold neutron beams

International Nuclear Information System (INIS)

Littrell, K. C.; Velthuis, S. G. E. te; Felcher, G. P.; Park, S.; Kirby, B. J.; Fitzsimmons, M. R.

2007-01-01

Biconcave cylindrical lenses are used to focus beams of x rays or neutrons using the refractive properties of matter. In the case of neutrons, the refractive properties of magnetic induction can similarly focus and simultaneously polarize the neutron beam without the concomitant attenuation of matter. This concept of a magnetic refractive lens was tested using a compound lens consisting of 99 pairs of cylindrical permanent magnets. The assembly successfully focused the intensity of a white beam of cold neutrons of one spin state at the detector, while defocusing the other. This experiment confirmed that a lens of this nature may boost the intensity locally by almost an order of magnitude and create a polarized beam. An estimate of the performance of a more practically dimensioned device suitable for incorporation in reflectometers and slit-geometry small angle scattering instruments is given

Magnetic compound refractive lens for focusing and polarizing cold neutron beams.

Science.gov (United States)

Littrell, K C; te Velthuis, S G E; Felcher, G P; Park, S; Kirby, B J; Fitzsimmons, M R

2007-03-01

Biconcave cylindrical lenses are used to focus beams of x rays or neutrons using the refractive properties of matter. In the case of neutrons, the refractive properties of magnetic induction can similarly focus and simultaneously polarize the neutron beam without the concomitant attenuation of matter. This concept of a magnetic refractive lens was tested using a compound lens consisting of 99 pairs of cylindrical permanent magnets. The assembly successfully focused the intensity of a white beam of cold neutrons of one spin state at the detector, while defocusing the other. This experiment confirmed that a lens of this nature may boost the intensity locally by almost an order of magnitude and create a polarized beam. An estimate of the performance of a more practically dimensioned device suitable for incorporation in reflectometers and slit-geometry small angle scattering instruments is given.

Rainbow refractometry on particles with radial refractive index gradients

Energy Technology Data Exchange (ETDEWEB)

Saengkaew, Sawitree [CNRS/Universite et INSA de Rouen, UMR 6614/CORIA, BP12, 76 800, Saint Etienne du Rouvray CEDEX (France); Chulalongkorn University, Center of Excellence in Particle Technology, Faculty of Engineering, Bangkok (Thailand); Charinpanitkul, Tawatchai; Vanisri, Hathaichanok; Tanthapanichakoon, Wiwut [Chulalongkorn University, Center of Excellence in Particle Technology, Faculty of Engineering, Bangkok (Thailand); Biscos, Yves; Garcia, Nicolas; Lavergne, Gerard [ONERA/DMAE, Toulouse (France); Mees, Loic; Gouesbet, Gerard; Grehan, Gerard [CNRS/Universite et INSA de Rouen, UMR 6614/CORIA, BP12, 76 800, Saint Etienne du Rouvray CEDEX (France)

2007-10-15

The rainbow refractrometry, under its different configurations (classical and global), is an attractive technique to extract information from droplets in evaporation such as diameter and temperature. Recently a new processing strategy has been developed which increases dramatically the size and refractive index measurements accuracy for homogeneous droplets. Nevertheless, for mono component as well as for multicomponent droplets, the presence of temperature and/or of concentration gradients induce the presence of a gradient of refractive index which affects the interpretation of the recorded signals. In this publication, the effect of radial gradient on rainbow measurements with a high accuracy never reached previously is quantified. (orig.)

Negative refraction at infrared wavelengths in a two-dimensional photonic crystal

International Nuclear Information System (INIS)

Berrier, A.; Mulot, M.; Swillo, M.; Qiu, M.; Thylen, L.; Anand, S.; Talneau, A.

2004-01-01

We report on the first experimental evidence of negative refraction at telecommunication wavelengths by a two-dimensional photonic crystal field. Samples were fabricated by chemically assisted ion beam etching in the InP-based low-index constrast system. Experiments of beam imaging and light collection show light focusing by the photonic crystal field. Finite-difference time-domain simulations confirm that the observed focusing is due to negative refraction in the photonic crystal area

Laser photo-reflectance characterization of resonant nonlinear electro-refraction in thin semiconductor films

International Nuclear Information System (INIS)

Chism, Will; Cartwright, Jason

2012-01-01

Photo-reflectance (PR) measurements provide a non-contact means for the precise characterization of semiconductor electronic properties. In this paper, we investigate the use of a laser beam as the probe beam in the PR setup. In this case it is seen that the nonlinear refraction is responsible for the amplitude change of the reflected probe field, whereas the phase change is due to nonlinear absorption. The open aperture condition may then be used to eliminate the spatial phase at the detector, thereby isolating the electro-refractive contribution to the PR signal. This greatly simplifies the PR analysis and allows absolute measurements of electro-refraction in thin semiconductor films. We report the application of the laser PR technique to characterize physical strain in thin silicon on silicon-germanium films. - Highlights: ► We describe the theory of laser photoreflectance. ► Laser photoreflectance is used to independently characterize nonlinear refraction. ► We report the characterization of strain in thin strained silicon films.

Giant Kerr nonlinearities using refractive-index enhancement

International Nuclear Information System (INIS)

Yavuz, D. D.; Sikes, D. E.

2010-01-01

By utilizing refractive-index enhancement with vanishing absorption, a scheme is suggested that achieves giant Kerr nonlinearities between two weak laser beams. One application of this scheme is discussed and an all-optical distributed Bragg reflector is proposed that works at very low light levels.

Risk factors for refractive errors in primary school children (6-12 years old) in Nakhon Pathom Province.

Science.gov (United States)

Yingyong, Penpimol

2010-11-01

Refractive error is one of the leading causes of visual impairment in children. An analysis of risk factors for refractive error is required to reduce and prevent this common eye disease. To identify the risk factors associated with refractive errors in primary school children (6-12 year old) in Nakhon Pathom province. A population-based cross-sectional analytic study was conducted between October 2008 and September 2009 in Nakhon Pathom. Refractive error, parental refractive status, and hours per week of near activities (studying, reading books, watching television, playing with video games, or working on the computer) were assessed in 377 children who participated in this study. The most common type of refractive error in primary school children was myopia. Myopic children were more likely to have parents with myopia. Children with myopia spend more time at near activities. The multivariate odds ratio (95% confidence interval)for two myopic parents was 6.37 (2.26-17.78) and for each diopter-hour per week of near work was 1.019 (1.005-1.033). Multivariate logistic regression models show no confounding effects between parental myopia and near work suggesting that each factor has an independent association with myopia. Statistical analysis by logistic regression revealed that family history of refractive error and hours of near-work were significantly associated with refractive error in primary school children.

Relationship between surface tension and refractive index in binary non-electrolyte mixtures

International Nuclear Information System (INIS)

Acevedo, I.L.; Pedrosa, G.C.; Katz, M.

1990-01-01

Lorentz-Lorenz equation for molecular refraction has been combined with Sugden's parachor equation for binary non-electrolyte mixtures at 298.15 K. The obtained equation has been shown successful in calculating values of surface tensions, by measuring refractive indices of the binary mixtures at the same mole fractions. The estimated error decreases when the mixtures present possible isorefractives. (Author) [es

Thickness-dependent dispersion parameters, energy gap and nonlinear refractive index of ZnSe thin films

International Nuclear Information System (INIS)

Prakash, Deo; Shaaban, E.R.; Shapaan, M.; Mohamed, S.H.; Othman, A.A.; Verma, K.D.

2016-01-01

Highlights: • Combined experimental and theoretical researches on ZnSe Thin Films. • The film thickness and refractive index were determined using envelope method. • The absorption coefficient and the energy gap were calculated. • Dispersion parameters were determined using Wemple-DiDomenico relation. • The third order susceptibility and nonlinear refractive index were calculated. - Abstract: Zinc selenide (ZnSe) thin films with different thicknesses were evaporated onto glass substrates using the thermal evaporation technique. X-ray diffraction analysis confirmed that both the film and powder have cubic zinc-blende structure. The fundamental optical parameters like absorption coefficient, extinction coefficient and band gap were evaluated in transparent region of transmittance and reflectance spectrum. The optical transition of the films was found to be allowed, where the energy gap increased from 2.576 to 2.702 eV with increasing film thickness. Also, the refractive index value increase with increasing film thickness. The refractive indices evaluated through envelope method were extrapolated by Cauchy dispersion relationship over the whole spectra range. Additionally, the dispersion of refractive index was determined in terms of Wemple-DiDomenico single oscillator model. Third order susceptibility and nonlinear refractive index were determined for different thickness of ZnSe thin films.

Thickness-dependent dispersion parameters, energy gap and nonlinear refractive index of ZnSe thin films

Energy Technology Data Exchange (ETDEWEB)

Prakash, Deo [School of Computer Science & Engineering, Faculty of Engineering, SMVD University, Kakryal, Katra 182320, J& K (India); Shaaban, E.R., E-mail: esam_ramadan2008@yahoo.com [Physics Department, Faculty of Science, Al-Azhar University, Assiut 71542 (Egypt); Shapaan, M. [Department of Physics, Faculty of Science, Al-Azahar University, Cairo (Egypt); Mohamed, S.H. [Physics Department, Faculty of Science, Sohag University, 82524 Sohag (Egypt); Othman, A.A. [Physics Department, Faculty of Science, Assiut University, Assiut 71516 (Egypt); Verma, K.D., E-mail: kdverma1215868@gmail.com [Material Science Research Laboratory, Department of Physics, S. V. College, Aligarh 202001, U.P. (India)

2016-08-15

Highlights: • Combined experimental and theoretical researches on ZnSe Thin Films. • The film thickness and refractive index were determined using envelope method. • The absorption coefficient and the energy gap were calculated. • Dispersion parameters were determined using Wemple-DiDomenico relation. • The third order susceptibility and nonlinear refractive index were calculated. - Abstract: Zinc selenide (ZnSe) thin films with different thicknesses were evaporated onto glass substrates using the thermal evaporation technique. X-ray diffraction analysis confirmed that both the film and powder have cubic zinc-blende structure. The fundamental optical parameters like absorption coefficient, extinction coefficient and band gap were evaluated in transparent region of transmittance and reflectance spectrum. The optical transition of the films was found to be allowed, where the energy gap increased from 2.576 to 2.702 eV with increasing film thickness. Also, the refractive index value increase with increasing film thickness. The refractive indices evaluated through envelope method were extrapolated by Cauchy dispersion relationship over the whole spectra range. Additionally, the dispersion of refractive index was determined in terms of Wemple-DiDomenico single oscillator model. Third order susceptibility and nonlinear refractive index were determined for different thickness of ZnSe thin films.

Prevalence of uncorrected refractive errors in adults aged 30 years and above in a rural population in Pakistan

International Nuclear Information System (INIS)

Abdullah, A.S.; Azam, M.; Nigar, M.

2015-01-01

Uncorrected refractive errors are a leading cause of visual disability globally. This population-based study was done to estimate the prevalence of uncorrected refractive errors in adults aged 30 years and above of village Pawakah, Khyber Pakhtunkhwa (KPK), Pakistan. Methods: It was a cross-sectional survey in which 1000 individuals were included randomly. All the individuals were screened for uncorrected refractive errors and those whose visual acuity (VA) was found to be less than 6/6 were refracted. In whom refraction was found to be unsatisfactory (i.e., a best corrected visual acuity of <6/6) further examination was done to establish the cause for the subnormal vision. Results: A total of 917 subjects participated in the survey (response rate 92%). The prevalence of uncorrected refractive errors was found to be 23.97% among males and 20% among females. The prevalence of visually disabling refractive errors was 6.89% in males and 5.71% in females. The prevalence was seen to increase with age, with maximum prevalence in 51-60 years age group. Hypermetropia (10.14%) was found to be the commonest refractive error followed by Myopia (6.00%) and Astigmatism (5.6%). The prevalence of Presbyopia was 57.5% (60.45% in males and 55.23% in females). Poor affordability was the commonest barrier to the use of spectacles, followed by unawareness. Cataract was the commonest reason for impaired vision after refractive correction. The prevalence of blindness was 1.96% (1.53% in males and 2.28% in females) in this community with cataract as the commonest cause. Conclusions: Despite being the most easily avoidable cause of subnormal vision uncorrected refractive errors still account for a major proportion of the burden of decreased vision in this area. Effective measures for the screening and affordable correction of uncorrected refractive errors need to be incorporated into the health care delivery system. (author)

Emittance of a finite scattering medium with refractive index greater than unity

International Nuclear Information System (INIS)

Crosbie, A.L.

1980-01-01

Refractive index and scattering can significantly influence the transfer of radiation in a semitransparent medium such as water, glass, plastics, or ceramics. In a recent article (1979), the author presented exact numerical results for the emittance of a semiinfinite scattering medium with a refractive index greater than unity. The present investigation extends the analysis to a finite medium. The physical situation consists of a finite planar layer. The isothermal layer emits, absorbs, and isotropically scatters thermal radiation. It is characterized by single scattering albedo, optical thickness, refractive index, and temperature. A formula for the directional emittance is derived, the directional emittance being the emittance of the medium multiplied by the interface transmittance. The ratio of hemispherical to normal emittance is tabulated and discussed

Spatial Frequency Multiplexing of Fiber-Optic Interferometric Refractive Index Sensors Based on Graded-Index Multimode Fibers

Science.gov (United States)

Liu, Li; Gong, Yuan; Wu, Yu; Zhao, Tian; Wu, Hui-Juan; Rao, Yun-Jiang

2012-01-01

Fiber-optic interferometric sensors based on graded-index multimode fibers have very high refractive-index sensitivity, as we previously demonstrated. In this paper, spatial-frequency multiplexing of this type of fiber-optic refractive index sensors is investigated. It is estimated that multiplexing of more than 10 such sensors is possible. In the multiplexing scheme, one of the sensors is used to investigate the refractive index and temperature responses. The fast Fourier transform (FFT) of the combined reflective spectra is analyzed. The intensity of the FFT spectra is linearly related with the refractive index and is not sensitive to the temperature.

Angularly symmetric splitting of a light beam upon reflection and refraction at an air-dielectric plane boundary: comment.

Science.gov (United States)

Andersen, Torben B

2016-05-01

In a recent paper, conditions for achieving equal and opposite angular deflections of a light beam by reflection and refraction at an interface between air and a dielectric were determined [J. Opt. Soc. Am. A32, 2436 (2015)JOAOD60740-323210.1364/JOSAA.32.002436]. The paper gives plots of angles of incidence and refraction as a function of the prism refractive index as well as plots of reflectances and incident linear-polarization azimuth angles as functions of the refractive index. We show here that it is possible to express these quantities as simple algebraic functions of the refractive index.

Public sector refraction and spectacle dispensing in low-resource countries of the Western Pacific.

Science.gov (United States)

Ramke, Jacqueline; du Toit, Rènée; Palagyi, Anna; Williams, Carmel; Brian, Garry

2008-05-01

Given that uncorrected refractive error is a frequent cause of vision impairment, and that there is a high unmet need for spectacles, an appraisal of public sector arrangements for the correction of refractive error was conducted in eight Pacific Island countries. Mixed methods (questionnaire and semi-structured interviews) were used to collect information from eye care personnel (from Fiji, Papua New Guinea, Solomon Islands, Vanuatu, Cook Islands, Samoa, Tonga and Tuvalu) attending a regional eye health workshop in 2005. Fiji, Tonga and Vanuatu had Vision 2020 eye care plans that included refraction services, but not spectacle provision. There was wide variation in public sector spectacle dispensing services, but, except in Samoa, ready-made spectacles and a full cost recovery pricing strategy were the mainstay. There were no systems for the registration of personnel, nor guidelines for clinical or systems management. The refraction staff to population ratio varied considerably. Solomon Islands, Tuvalu and Vanuatu had the best coverage by services, either fixed or outreach. Most services had little promotional activity or community engagement. To be successful, it would seem that public sector refraction services should answer a real and perceived need, fit within prevailing policy and legislation, value, train, retain and equip employees, be well managed, be accessible and affordable, be responsive to consumers, and provide ongoing good quality outcomes. To this end, a checklist to aid the initiation and maintenance of refraction and spectacle systems in low-resource countries has been constructed.

Real time refractive index measurement by ESPI

International Nuclear Information System (INIS)

Torroba, R.; Joenathan, C.

1991-01-01

In this paper a method to measure refractive index variations in real time is reported. A technique to introduce reference fringes in real time is discussed. Both the theoretical and experimental results are presented and an example with phase shifting is given. (author). 8 refs, 5 figs

seismic refraction investigation of the subsurface structure

African Journals Online (AJOL)

DR. AMINU

employed for exploration include magnetic, electrical and gravitational methods, which depends on the earth's natural fields. Others are seismic and electromagnetic methods, which depends on the introduction of artificial energy in thereof. The seismic refraction method uses the seismic energy that returns to the surface of ...

Interferometer for Measuring Fast Changes of Refractive Index and Temperature in Transparent Liquids

DEFF Research Database (Denmark)

Miller, Arne; Hussmann, E. K.; McLaughlin, W. L.

1975-01-01

A double‐beam interferometer has been designed for detecting changes of refractive index in transparent liquids associated with the absorption of ionizing radiation energy, due to short electron beam pulses from an accelerator. The response time of the interferometer is less than 0.2 μsec......, and refractive index changes of the order of 10−7 can be measured, corresponding to a temperature change of ∼10−3  °C and an absorbed dose in water of ∼350 rad. The interferometer can be used as either a real‐time or integrating radiation dosimeter, if the temperature coefficient of the refractive index (dn...

Characteristics of the thick, compound refractive lens

International Nuclear Information System (INIS)

Pantell, Richard H.; Feinstein, Joseph; Beguiristain, H. Raul; Piestrup, Melvin A.; Gary, Charles K.; Cremer, Jay T.

2003-01-01

A compound refractive lens (CRL), consisting of a series of N closely spaced lens elements each of which contributes a small fraction of the total focusing, can be used to focus x rays or neutrons. The thickness of a CRL can be comparable to its focal length, whereupon a thick-lens analysis must be performed. In contrast with the conventional optical lens, where the ray inside the lens follows a straight line, the ray inside the CRL is continually changing direction because of the multiple refracting surfaces. Thus the matrix representation for the thick CRL is quite different from that for the thick optical lens. Principal planes can be defined such that the thick-lens matrix can be converted to that of a thin lens. For a thick lens the focal length is greater than for a thin lens with the same lens curvature, but this lengthening effect is less for the CRL than for the conventional optical lens

Single Mode Optical Fiber based Refractive Index Sensor using Etched Cladding

OpenAIRE

Kumar, Ajay; Gupta, Geeta; Mallik, Arun; Bhatnagar, Anuj

2011-01-01

The use of optical fiber for sensor applications is a topic of current interest. We report the fabrication of etched single mode optical fiber based refractive index sensor. Experiments are performed to determine the etch rate of fiber in buffered hydrofluoric acid, which can be high or low depending upon the temperature at which etching is carried out. Controlled wet etching of fiber cladding is performed using these measurements and etched fiber region is tested for refractive index sensing...

High-precision diode-laser-based temperature measurement for air refractive index compensation

International Nuclear Information System (INIS)

Hieta, Tuomas; Merimaa, Mikko; Vainio, Markku; Seppae, Jeremias; Lassila, Antti

2011-01-01

We present a laser-based system to measure the refractive index of air over a long path length. In optical distance measurements, it is essential to know the refractive index of air with high accuracy. Commonly, the refractive index of air is calculated from the properties of the ambient air using either Ciddor or Edlen equations, where the dominant uncertainty component is in most cases the air temperature. The method developed in this work utilizes direct absorption spectroscopy of oxygen to measure the average temperature of air and of water vapor to measure relative humidity. The method allows measurement of temperature and humidity over the same beam path as in optical distance measurement, providing spatially well-matching data. Indoor and outdoor measurements demonstrate the effectiveness of the method. In particular, we demonstrate an effective compensation of the refractive index of air in an interferometric length measurement at a time-variant and spatially nonhomogeneous temperature over a long time period. Further, we were able to demonstrate 7 mK RMS noise over a 67 m path length using a 120 s sample time. To our knowledge, this is the best temperature precision reported for a spectroscopic temperature measurement.

Autorefraction versus subjective refraction in a radially asymmetric multifocal intraocular lens.

Science.gov (United States)

van der Linden, Jan Willem; Vrijman, Violette; Al-Saady, Rana; El-Saady, Rana; van der Meulen, Ivanka J; Mourits, Maarten P; Lapid-Gortzak, Ruth

2014-12-01

To evaluate whether the automated refraction (AR) correlates with subjective manifest (MR) refraction in eyes implanted with radially asymmetric multifocal intraocular lens (IOLs). This retrospective study evaluated 52 eyes (52 patients) implanted with a radially asymmetric multifocal IOL (LS-312 MF30, Oculentis, Germany). At 3 months postoperatively, the AR and MR values were compared to determine the correlation between the sphere (S), the spherical equivalent (SE) and the astigmatic components J0 and J45. The difference of mean spherical measurement was +0.98D ± 0.62, with the AR measuring more myopic. The difference of the mean spherical equivalent was +1.11D ± 0.57, again with AR being more myopic. Both these differences were statistically significant (p < 0.001). The astigmatic components showed less differences, with the mean difference of the J0 being -0.09D ± 0.43, and the J45 of +0.04D ± 0.47, which were both not statistically significant (p = 0.123 and p = 0.531, respectively). Correlation analysis of the refractive parameters showed r(2) = 0.067, r(2) = 0.078, r(2) = 0.018 and r(2) = 0.015, respectively, all of which point to a low correlation between the AR and the MR. Autorefraction shows poor correlation to manifest subjective refraction with these radially asymmetric multifocal IOLs. The autorefraction systematically underestimates the spherical and spherical equivalent power, while the correlation between the astigmatic components was also low. Autorefraction seems not a valid starting point for manifest subjective refraction with these types of lenses, unless a corrective factor of about +1 dioptre is used. © 2014 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

The New Zealand cataract and refractive surgery survey 1997/1998.

Science.gov (United States)

Elder, M; Tarr, K; Leaming, D

2000-04-01

This study documents the current practice for cataract and refractive surgery in New Zealand. A postal questionnaire was distributed in late 1997 to all consultant members of the Ophthalmological Society of New Zealand that were resident in the country at that time. Most questions were identical to the 1997 survey of the American Society of Cataract and Refraction Surgeons (ASCRS) to enable a comparison. There were 98 returns from 101 surveys distributed. Of the returns, 72 performed cataract surgery, 23 performed PRK and 11 performed LASIK. ASCRS members did more refractive surgery than did New Zealanders: 28 versus 1% of 1-5 RK per month, 7 versus 1% of 1-2 clear lens extractions per month and 85 versus 51% had access to an excimer laser. For cataract surgery, ASCRS members used more topical anaesthesia (30 vs 5.5%), used no sutures more often (73 vs 51%), used more preoperative antibiotics (76 vs 26%) and used fewer injections of antibiotic/steroids (38 vs 61%). Otherwise the two groups were broadly similar.

Association between Ocular Sensory Dominance and Refractive Error Asymmetry.

Directory of Open Access Journals (Sweden)

Feng Jiang

Full Text Available To investigate the association between ocular sensory dominance and interocular refractive error difference (IRED.A total of 219 subjects were recruited. The refractive errors were determined by objective refraction with a fixation target located 6 meters away. 176 subjects were myopic, with 83 being anisometropic (IRED ≥ 0.75 D. 43 subjects were hyperopic, with 22 being anisometropic. Sensory dominance was measured with a continuous flashing technique with the tested eye viewing a Gabor increasing in contrast and the fellow eye viewing a Mondrian noise decreasing in contrast. The log ratio of Mondrian to Gabor's contrasts was recorded when a subject just detected the tilting direction of the Gabor during each trial. T-test was used to compare the 50 values collected from each eye, and the t-value was used as a subject's ocular dominance index (ODI to quantify the degree of ocular dominance. A subject with ODI ≥ 2 (p < 0.05 had clear dominance and the eye with larger mean ratio was the dominant one. Otherwise, a subject had an unclear dominance.The anisometropic subjects had stronger ocular dominance in comparison to non-anisometropic subjects (rank-sum test, p < 0.01 for both myopic and hyperopic subjects. In anisometropic subjects with clear dominance, the amplitude of the anisometropia was correlated with ODI values (R = 0.42, p < 0.01 in myopic anisometropic subjects; R = 0.62, p < 0.01 in hyperopic anisometropic subjects. Moreover, the dominant eyes were more myopic in myopic anisometropic subjects (sign-test, p < 0.05 and less hyperopic in hyperopic anisometropic subjects (sign-test, p < 0.05.The degree of ocular sensory dominance is associated with interocular refractive error difference.

Atmospheric stability index using radio occultation refractivity profiles

Indian Academy of Sciences (India)

A new stability index based on atmospheric refractivity at ∼500 hPa level and surface measurements of temperature ... able at different heights rather than pressure levels. However ..... the radio occultation technique being a limb sound-.

Refractive Index Measurement within a Photonic Crystal Fibre Based on Short Wavelength Diffraction

Directory of Open Access Journals (Sweden)

Nathaniel Groothoff

2007-10-01

Full Text Available A new class of refractive index sensors using solid core photonic crystal fibres isdemonstrated. Coherent scattering at the cladding lattice is used to optically characterizematerials inserted into the fibre holes. The liquid to solid phase transition of water uponfreezing to ice 1h is characterized by determining the refractive index.

Light refraction in PbMgsub(1/3)Nbsub(2/3)Osub(3) ferroelectric with a diffuse phase transition

International Nuclear Information System (INIS)

Korshunov, O.Yu.; Markovin, P.A.; Pisarev, R.V.

1983-01-01

In PbMgsub(1/2)Nbsub(2/3)Osub(3) ferroelectric with a diffuse phase transition refractive indeX variations with temperature are studied for two wavelengths of 0.63 and 0.44 μm in the 140-600 K temperature range, and refractive index dispersion is measured at room temperature. A broad smooth peak of rate of light refraction temperation changes in the 300-310 K range that coincides with the previously observed by other authors on the temperatUre dependence of microwave dielectric permittivity. A refractive properties anomaly is also observed at 156 K that is related with another phase transition at this temperature. Mechanisms of refractive index thermal variations are analyzed and a ferroelectric contribution into light refraction that equals approximately 4x10 -2 at 140 K is found. The contribution remains up to 600 K due to polarization fluctuations. It is shown that within the frames of dispersion theory the effect of ferroelectric ordering on light refraction can be explained by changes of both frequency and effective oscillator force

Refractive index sensor based on optical fiber end face using pulse reference-based compensation technique

Science.gov (United States)

Bian, Qiang; Song, Zhangqi; Zhang, Xueliang; Yu, Yang; Chen, Yuzhong

2018-03-01

We proposed a refractive index sensor based on optical fiber end face using pulse reference-based compensation technique. With good compensation effect of this compensation technique, the power fluctuation of light source, the change of optic components transmission loss and coupler splitting ratio can be compensated, which largely reduces the background noise. The refractive index resolutions can achieve 3.8 × 10-6 RIU and1.6 × 10-6 RIU in different refractive index regions.

Refraction-enhanced backlit imaging of axially symmetric inertial confinement fusion plasmas.

Science.gov (United States)

Koch, Jeffrey A; Landen, Otto L; Suter, Laurence J; Masse, Laurent P; Clark, Daniel S; Ross, James S; Mackinnon, Andrew J; Meezan, Nathan B; Thomas, Cliff A; Ping, Yuan

2013-05-20

X-ray backlit radiographs of dense plasma shells can be significantly altered by refraction of x rays that would otherwise travel straight-ray paths, and this effect can be a powerful tool for diagnosing the spatial structure of the plasma being radiographed. We explore the conditions under which refraction effects may be observed, and we use analytical and numerical approaches to quantify these effects for one-dimensional radial opacity and density profiles characteristic of inertial-confinement fusion (ICF) implosions. We also show how analytical and numerical approaches allow approximate radial plasma opacity and density profiles to be inferred from point-projection refraction-enhanced radiography data. This imaging technique can provide unique data on electron density profiles in ICF plasmas that cannot be obtained using other techniques, and the uniform illumination provided by point-like x-ray backlighters eliminates a significant source of uncertainty in inferences of plasma opacity profiles from area-backlit pinhole imaging data when the backlight spatial profile cannot be independently characterized. The technique is particularly suited to in-flight radiography of imploding low-opacity shells surrounding hydrogen ice, because refraction is sensitive to the electron density of the hydrogen plasma even when it is invisible to absorption radiography. It may also provide an alternative approach to timing shockwaves created by the implosion drive, that are currently invisible to absorption radiography.

Effect of TiCl4 treatment on the refractive index of nanoporous TiO2 films

Science.gov (United States)

Lee, Jeeyoung; Lee, Myeongkyu

2015-12-01

We investigate the effect of TiCl4 treatment on the refractive index of a nanoporous TiO2 film. A nanoparticulate TiO2 film prepared on a glass substrate was immersed in a TiCl4 aqueous solution. The subsequent reaction of TiCl4 with H2O produces TiO2 and thus modifies the density and the refractive index of the film. With increasing TiCl4 concentration, the refractive index initially increased and then declined after being maximized (n = 2.02 at 633 nm) at 0.08 M concentration. A refractive index change as large as 0.45 could be obtained with the TiCl4 treatment, making it possible to achieve diffraction efficiency exceeding 80% in a diffraction grating-embedded TiO2 film. For high TiCl4 concentrations of 0.32 M and 0.64 M, the refractive index remained nearly unchanged. This was attributed to the limited permeability of high-viscosity TiCl4 solutions into the nanoporous films. The measured pore size distributions were in good agreement with the results of a diffraction analysis and refractive index measurement.

Refractive error, ocular biometry, and lens opalescence in an adult population: the Los Angeles Latino Eye Study.

Science.gov (United States)

Shufelt, Chrisandra; Fraser-Bell, Samantha; Ying-Lai, Mei; Torres, Mina; Varma, Rohit

2005-12-01

To characterize age- and gender-related differences in refractive error, ocular biometry, and lens opalescence (NOP) in a population-based sample of adult Latinos. Also assessed were the determinants of age-related refractive differences. Participants in the Los Angeles Latino Eye Study (LALES), a population-based study of Latinos aged 40 years and more, underwent an ophthalmic examination, including ultrasonic measurements of axial length (AL), vitreous chamber depth (VCD), anterior chamber depth (ACD), lens thickness (LT), and noncycloplegic automated and subjective refraction. Corneal curvature/power (CP) was measured using an autorefractor. NOP was graded at the slit lamp by an ophthalmologist using the Lens Opacity Classification System II. Age- and gender-related differences were calculated. Multiple regression models were used to identify the determinants of age-related refractive differences. Of the 6357 LALES participants, 5588 phakic individuals with biometric data were included in this analysis. Older individuals had shallower ACDs, thicker lenses, more NOP, and more hyperopia compared to younger individuals (P or = 0.05). Women had significantly shorter AL, shallower ACD and VCD, than did men (P < or = 0.01). The strongest determinants of refractive error were AL (primarily VCD) and CP. NOP was a small but significant determinant of refractive error in older individuals. Age- and gender-related differences in ocular biometric, refractive error, and NOP measurements are present in adult Latinos. While the relative contribution of NOP in determining refractive error is small, it is greater in older persons compared to younger individuals.

Refractometers for different refractive index range by surface plasmon resonance sensors in multimode optical fibers with different metals

Science.gov (United States)

Zuppella, P.; Corso, Alain J.; Pelizzo, Maria G.; Cennamo, N.; Zeni, L.

2016-09-01

We have realized a plasmonic sensor based on Au/Pd metal bilayer in a multimode plastic optical fiber. This metal bilayer, based on a metal with high imaginary part of the refractive index and gold, shows interesting properties in terms of sensitivity and performances, in different refractive index ranges. The development of highly sensitive platforms for high refractive index detection (higher than 1.38) is interesting for chemical applications based on molecularly imprinted polymer as receptors, while the aqueous medium is the refractive index range of biosensors based on bio-receptors. In this work we have presented an Au/Pd metal bilayer optimized for 1.38-1.42 refractive index range.

Hugoniot and refractive indices of bromoform under shock compression

Science.gov (United States)

Liu, Q. C.; Zeng, X. L.; Zhou, X. M.; Luo, S. N.

2018-01-01

We investigate physical properties of bromoform (liquid CHBr3) including compressibility and refractive index under dynamic extreme conditions of shock compression. Planar shock experiments are conducted along with high-speed laser interferometry. Our experiments and previous results establish a linear shock velocity-particle velocity relation for particle velocities below 1.77 km/s, as well as the Hugoniot and isentropic compression curves up to ˜21 GPa. Shock-state refractive indices of CHBr3 up to 2.3 GPa or ˜26% compression, as a function of density, can be described with a linear relation and follows the Gladstone-Dale relation. The velocity corrections for laser interferometry measurements at 1550 nm are also obtained.

Hugoniot and refractive indices of bromoform under shock compression

Directory of Open Access Journals (Sweden)

Q. C. Liu

2018-01-01

Full Text Available We investigate physical properties of bromoform (liquid CHBr3 including compressibility and refractive index under dynamic extreme conditions of shock compression. Planar shock experiments are conducted along with high-speed laser interferometry. Our experiments and previous results establish a linear shock velocity−particle velocity relation for particle velocities below 1.77 km/s, as well as the Hugoniot and isentropic compression curves up to ∼21 GPa. Shock-state refractive indices of CHBr3 up to 2.3 GPa or ∼26% compression, as a function of density, can be described with a linear relation and follows the Gladstone-Dale relation. The velocity corrections for laser interferometry measurements at 1550 nm are also obtained.

[Complications after refractive surgery abroad].

Science.gov (United States)

Terzi, E; Kern, T; Kohnen, T

2008-05-01

In this article a retrospective analysis of patients presenting at a German university following refractive surgery abroad is presented. A total of 20 cases of patients who had undergone treatment between 1998 and 2006 in China (1 case), Greece (1 case), Iran (1 case), Russia (2 cases), Switzerland (1 case), Slovakia (1 case), Spain (2 cases), South Africa (3 cases), Turkey (6 cases) and the USA (2 cases) were analyzed retrospectively. The following complications were observed: epithelial ingrowth into the interface with or without melting of the flap (6 cases), corneal ectasia (2 cases), dislocation of a phakic posterior chamber intraocular lens and prolapse into the anterior chamber with endothelial cell loss (1 case), secondary increase of intraocular pressure following implantation of a phakic intraocular lens (1 case), flap-related complications following laser-in-situ keratomileusis (LASIK) (2 cases), keratitis (1 case), dislocation of the complete flap (1 case), diffuse lamellar keratitis (DLK) grade IV (1 case), hyperopia as a consequence of radial keratotomy (1 case), and under correction/over correction and poor optical quality following laser epithelial keratomileusis (LASEK) and LASIK for high myopia (5 cases) with possible early corneal ectasia. There are four important problems arising from refractive surgery abroad, often referred to as "LASIK tourism": wrong indications, insufficient management of complications, lack of postoperative care and the health economic aspect.

The prevalence of refractive conditions in Puerto Rican adults attending an eye clinic system

Directory of Open Access Journals (Sweden)

Neisha M. Rodriguez

2014-07-01

Conclusion: Hyperopia is the most common refractive error and its prevalence and seems to increase among the aging population who visited the clinics. Further programs and studies must be developed to address the refractive errors needs of the adult Puerto Rican population.

Refractive index sensor based on a 1D photonic crystal in a microfluidic channel

DEFF Research Database (Denmark)

Rodrigues de Sousa Nunes, Pedro André; Mortensen, Asger; Kutter, Jörg Peter

2010-01-01

A refractive index sensor has been fabricated in silicon oxynitride by standard UV lithography and dry etching processes. The refractive index sensor consists of a 1D photonic crystal (PhC) embedded in a microfluidic channel addressed by fiber-terminated planar waveguides. Experimental...

Deep-water bedforms induced by refracting Internal Solitary Waves

Science.gov (United States)

Falcini, Federico; Droghei, Riccardo; Casalbore, Daniele; Martorelli, Eleonora; Mosetti, Renzo; Sannino, Gianmaria; Santoleri, Rosalia; Latino Chiocci, Francesco

2017-04-01

Subaqueous bedforms (or sand waves) are typically observed in those environments that are exposed to strong currents, characterized by a dominant unidirectional flow. However, sand-wave fields may be also observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs), induced by tides, can produce an effective, unidirectional boundary flow filed that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

The effects of refraction on transit transmission spectroscopy: application to Earth-like exoplanets

Energy Technology Data Exchange (ETDEWEB)

Misra, Amit; Meadows, Victoria [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195 (United States); Crisp, Dave, E-mail: amit0@astro.washington.edu [NAI Virtual Planetary Laboratory, Seattle, WA (United States)

2014-09-01

We quantify the effects of refraction in transit transmission spectroscopy on spectral absorption features and on temporal variations that could be used to obtain altitude-dependent spectra for planets orbiting stars of different stellar types. We validate our model against altitude-dependent transmission spectra of the Earth from ATMOS and against lunar eclipse spectra from Pallé et al. We perform detectability studies to show the potential effects of refraction on hypothetical observations of Earth analogs with the James Webb Space Telescope NIRSPEC. Due to refraction, there will be a maximum tangent pressure level that can be probed during transit for each given planet-star system. We show that because of refraction, for an Earth-analog planet orbiting in the habitable zone of a Sun-like star only the top 0.3 bars of the atmosphere can be probed, leading to a decrease in the signal-to-noise ratio (S/N) of absorption features by 60%, while for an Earth-analog planet orbiting in the habitable zone of an M5V star it is possible to probe almost the entire atmosphere with minimal decreases in S/N. We also show that refraction can result in temporal variations in the transit transmission spectrum which may provide a way to obtain altitude-dependent spectra of exoplanet atmospheres. Additionally, the variations prior to ingress and subsequent to egress provide a way to probe pressures greater than the maximum tangent pressure that can be probed during transit. Therefore, probing the maximum range of atmospheric altitudes, and in particular the near-surface environment of an Earth-analog exoplanet, will require looking at out-of-transit refracted light in addition to the in-transit spectrum.

The effects of refraction on transit transmission spectroscopy: application to Earth-like exoplanets

International Nuclear Information System (INIS)

Misra, Amit; Meadows, Victoria; Crisp, Dave

2014-01-01

We quantify the effects of refraction in transit transmission spectroscopy on spectral absorption features and on temporal variations that could be used to obtain altitude-dependent spectra for planets orbiting stars of different stellar types. We validate our model against altitude-dependent transmission spectra of the Earth from ATMOS and against lunar eclipse spectra from Pallé et al. We perform detectability studies to show the potential effects of refraction on hypothetical observations of Earth analogs with the James Webb Space Telescope NIRSPEC. Due to refraction, there will be a maximum tangent pressure level that can be probed during transit for each given planet-star system. We show that because of refraction, for an Earth-analog planet orbiting in the habitable zone of a Sun-like star only the top 0.3 bars of the atmosphere can be probed, leading to a decrease in the signal-to-noise ratio (S/N) of absorption features by 60%, while for an Earth-analog planet orbiting in the habitable zone of an M5V star it is possible to probe almost the entire atmosphere with minimal decreases in S/N. We also show that refraction can result in temporal variations in the transit transmission spectrum which may provide a way to obtain altitude-dependent spectra of exoplanet atmospheres. Additionally, the variations prior to ingress and subsequent to egress provide a way to probe pressures greater than the maximum tangent pressure that can be probed during transit. Therefore, probing the maximum range of atmospheric altitudes, and in particular the near-surface environment of an Earth-analog exoplanet, will require looking at out-of-transit refracted light in addition to the in-transit spectrum.

Overlapping illusions by transformation optics without any negative refraction material

Science.gov (United States)

Sun, Fei; He, Sailing

2016-01-01

A novel method to achieve an overlapping illusion without any negative refraction index material is introduced with the help of the optic-null medium (ONM) designed by an extremely stretching spatial transformation. Unlike the previous methods to achieve such an optical illusion by transformation optics (TO), our method can achieve a power combination and reshape the radiation pattern at the same time. Unlike the overlapping illusion with some negative refraction index material, our method is not sensitive to the loss of the materials. Other advantages over existing methods are discussed. Numerical simulations are given to verify the performance of the proposed devices.

Infrared refractive index of thin YBa2Cu3O7 superconducting films

International Nuclear Information System (INIS)

Zhang, Z.M.; Choi, B.I.; Le, T.A.; Flik, M.I.; Siegal, M.P.; Phillips, J.M.

1992-01-01

This work investigates whether thin-film optics with a constant refractive index can be applied to high-T c superconducting thin films. The reflectance and transmittance of YBa 2 Cu 3 O 7 films on LaAlO 3 substrates are measured using a Fourier-transform infrared spectrometer at wavelengths from 1 to 100 μm at room temperature. The reflectance of these superconducting films at 10K in the wavelength region from 2.5 to 25 μm is measured using a cryogenic reflectance accessory. The film thickness varies from 10 to 200 nm. By modeling the frequency-dependent complex conductivity in the normal and superconducting states and applying electromagnetic-wave theory, the complex refractive index of YBa 2 Cu 3 O 7 films is obtained with a fitting technique. It is found that a thickness-independent refractive index can be applied even to a 25nm film, and average values of the spectral refractive index for film thicknesses between 25 and 200 nm are recommended for engineering applications

Refractive Secondary Solar Concentrator Being Designed and Developed

Science.gov (United States)

Macosko, Robert P.; Donovan, Richard M.

1998-01-01

As the need for achieving super high temperatures (2000 K and above) in solar heat receivers has developed so has the need for secondary concentrators. These concentrators refocus the already highly concentrated solar energy provided by a primary solar collector, thereby significantly reducing the light entrance aperture of the heat receiver and the resulting infrared radiation heat loss from the receiver cavity. Although a significant amount of research and development has been done on nonimaging hollow reflective concentrators, there has been no other research or development to date on solid, single crystal, refractive concentrators that can operate at temperatures above 2000 K. The NASA Lewis Research Center recently initiated the development of single-crystal, optically clear, refractive secondary concentrators that, combined with a flux extractor, offer a number of significant advantages over the more conventional, hollow, reflective concentrators at elevated temperatures. Such concentrators could potentially provide higher throughput (efficiency), require no special cooling device, block heat receiver material boiloff from the receiver cavity, provide for flux tailoring in the cavity via the extractor, and potentially reduce infrared heat loss via an infrared block coating.The many technical challenges of designing and fabricating high-temperature refractive secondary concentrators and flux extractors include identifying optical materials that can survive the environment (high-temperature, vacuum and/or hydrogen atmosphere), developing coatings for enhanced optical and thermal performance, and developing crystal joining techniques and hardware that can survive launch loads.

Rectification of light refraction in curved waveguide arrays.

Science.gov (United States)

Longhi, Stefano

2009-02-15

An "optical ratchet" for discretized light in photonic lattices, which enables observing rectification of light refraction at any input beam conditions, is theoretically presented, and a possible experimental implementation based on periodically curved zigzag waveguide arrays is proposed.

Application of super-virtual seismic refraction interferometry to enhance first arrivals: A case study from Saudi Arabia

KAUST Repository

Alshuhail, Abdulrahman Abdullatif Abdulrahman

2012-01-01

Complex near-surface anomalies are one of the main onshore challenges facing seismic data processors. Refraction tomography is becoming a common technology to estimate an accurate near-surface velocity model. This process involves picking the first arrivals of refracted waves. One of the main challenges with refraction tomography is the low signal-to-noise ratio characterizing the first-break waveform arrivals, especially for the far-offset receivers. This is especially evident in data recorded using reflection acquisition geometry. This low signal-to-noise ratio is caused by signal attenuation due to geometrical spreading of the seismic wavefield, near-surface-generated noise, and amplitude absorption. Super-virtual refraction interferometry improves the quality of the first-break picks by enhancing the amplitude of the refracted waves and attenuating the amplitude of the random noise.

Variable discrete ordinates method for radiation transfer in plane-parallel semi-transparent media with variable refractive index

Science.gov (United States)

Sarvari, S. M. Hosseini

2017-09-01

The traditional form of discrete ordinates method is applied to solve the radiative transfer equation in plane-parallel semi-transparent media with variable refractive index through using the variable discrete ordinate directions and the concept of refracted radiative intensity. The refractive index are taken as constant in each control volume, such that the direction cosines of radiative rays remain non-variant through each control volume, and then, the directions of discrete ordinates are changed locally by passing each control volume, according to the Snell's law of refraction. The results are compared by the previous studies in this field. Despite simplicity, the results show that the variable discrete ordinate method has a good accuracy in solving the radiative transfer equation in the semi-transparent media with arbitrary distribution of refractive index.

Refracting Schoolgirls: Pedagogical Intra-Actions Producing Shame

Science.gov (United States)

Wolfe, Melissa Joy

2017-01-01

This article contributes to the discussion of gender inequality in schools with the central theme tracing ways that pedagogical affect im/mobilises agency. I argue that what I call "the schoolgirl affect," as distinctly gendered pedagogical practices in schools, constitute a schoolgirl body that refracts capacity for action in particular…

Refractive Status at Birth: Its Relation to Newborn Physical Parameters at Birth and Gestational Age

Science.gov (United States)

Varghese, Raji Mathew; Sreenivas, Vishnubhatla; Puliyel, Jacob Mammen; Varughese, Sara

2009-01-01

Background Refractive status at birth is related to gestational age. Preterm babies have myopia which decreases as gestational age increases and term babies are known to be hypermetropic. This study looked at the correlation of refractive status with birth weight in term and preterm babies, and with physical indicators of intra-uterine growth such as the head circumference and length of the baby at birth. Methods All babies delivered at St. Stephens Hospital and admitted in the nursery were eligible for the study. Refraction was performed within the first week of life. 0.8% tropicamide with 0.5% phenylephrine was used to achieve cycloplegia and paralysis of accommodation. 599 newborn babies participated in the study. Data pertaining to the right eye is utilized for all the analyses except that for anisometropia where the two eyes were compared. Growth parameters were measured soon after birth. Simple linear regression analysis was performed to see the association of refractive status, (mean spherical equivalent (MSE), astigmatism and anisometropia) with each of the study variables, namely gestation, length, weight and head circumference. Subsequently, multiple linear regression was carried out to identify the independent predictors for each of the outcome parameters. Results Simple linear regression showed a significant relation between all 4 study variables and refractive error but in multiple regression only gestational age and weight were related to refractive error. The partial correlation of weight with MSE adjusted for gestation was 0.28 and that of gestation with MSE adjusted for weight was 0.10. Birth weight had a higher correlation to MSE than gestational age. Conclusion This is the first study to look at refractive error against all these growth parameters, in preterm and term babies at birth. It would appear from this study that birth weight rather than gestation should be used as criteria for screening for refractive error, especially in developing

Refractive status at birth: its relation to newborn physical parameters at birth and gestational age.

Directory of Open Access Journals (Sweden)

Raji Mathew Varghese

Full Text Available Refractive status at birth is related to gestational age. Preterm babies have myopia which decreases as gestational age increases and term babies are known to be hypermetropic. This study looked at the correlation of refractive status with birth weight in term and preterm babies, and with physical indicators of intra-uterine growth such as the head circumference and length of the baby at birth.All babies delivered at St. Stephens Hospital and admitted in the nursery were eligible for the study. Refraction was performed within the first week of life. 0.8% tropicamide with 0.5% phenylephrine was used to achieve cycloplegia and paralysis of accommodation. 599 newborn babies participated in the study. Data pertaining to the right eye is utilized for all the analyses except that for anisometropia where the two eyes were compared. Growth parameters were measured soon after birth. Simple linear regression analysis was performed to see the association of refractive status, (mean spherical equivalent (MSE, astigmatism and anisometropia with each of the study variables, namely gestation, length, weight and head circumference. Subsequently, multiple linear regression was carried out to identify the independent predictors for each of the outcome parameters.Simple linear regression showed a significant relation between all 4 study variables and refractive error but in multiple regression only gestational age and weight were related to refractive error. The partial correlation of weight with MSE adjusted for gestation was 0.28 and that of gestation with MSE adjusted for weight was 0.10. Birth weight had a higher correlation to MSE than gestational age.This is the first study to look at refractive error against all these growth parameters, in preterm and term babies at birth. It would appear from this study that birth weight rather than gestation should be used as criteria for screening for refractive error, especially in developing countries where the

Negative refraction imaging of acoustic metamaterial lens in the supersonic range

Directory of Open Access Journals (Sweden)

Jianning Han

2014-05-01

Full Text Available Acoustic metamaterials with negative refraction index is the most promising method to overcome the diffraction limit of acoustic imaging to achieve ultrahigh resolution. In this paper, we use localized resonant phononic crystal as the unit cell to construct the acoustic negative refraction lens. Based on the vibration model of the phononic crystal, negative quality parameters of the lens are obtained while excited near the system resonance frequency. Simulation results show that negative refraction of the acoustic lens can be achieved when a sound wave transmiting through the phononic crystal plate. The patterns of the imaging field agree well with that of the incident wave, while the dispersion is very weak. The unit cell size in the simulation is 0.0005 m and the wavelength of the sound source is 0.02 m, from which we show that acoustic signal can be manipulated through structures with dimensions much smaller than the wavelength of incident wave.

Refractive index dependent local electric field enhancement in cylindrical gold nanohole

International Nuclear Information System (INIS)

Zhu Jian

2011-01-01

We report on the local electric field characters in a long cylindrical gold nanohole. Theoretical calculation results based on quasi-static model show that the local environmental dielectric constant dependent electric field intensity and field distribution in the gold nanohole show quite unique properties, different from those in the thin gold nanotube. Because of the thick gold wall, no plasmon hybridization exists. So there is only one resonance frequency taking place, and the intense local field has been focused into the gold nanohole. Our main finding is that, the local field in the nanohole is largely dependent on the inner hole refractive index and outer environmental refractive index. The competition between inner hole and outer polarization leads to a non-monotonic change of the local field intensity with increasing the dielectric constant of the nanohole. This refractive index controlled local field enhancement in cylindrical gold nanohole presents a potential for tunable surface-enhanced fluorescence and novel nano-optical biosensing applications.

Diffraction limit of refractive compound lens

International Nuclear Information System (INIS)

Kolchevsky, N.N.; Petrov, P.V.

2015-01-01

A compound X-ray and neutron lenses is an array of lenses with a common axis. The resolution limited by aberration and by diffraction. Diffraction limit comes from theory based on absorption aperture of the compound refractive lenses. Beam passing through transparent lenses form Airy pattern. Results of calculation of diffraction resolution limit for non-transparent X-ray and neutron lenses are discussed. (authors)

Low-reflection beam refractions by ultrathin Huygens metasurface

International Nuclear Information System (INIS)

Jia, Sheng Li; Wan, Xiang; Fu, Xiao Jian; Zhao, Yong Jiu; Cui, Tie Jun

2015-01-01

We propose a Huygens source unit cell to develop an ultrathin low-reflection metasurface, which could provide extreme controls of phases of the transmitted waves. Both electric and magnetic currents are supported by the proposed unit cell, thus leading to highly efficient and full controls of phases. The coupling between electric and magnetic responses is negligible, which will significantly reduce the difficulty of design. Since the unit cell of metasurface is printed on two bonded boards, the fabrication process is simplified and the thickness of metasurface is reduced. Based on the proposed unit cell, a beam-refracting metasurface with low-reflection is designed and manufactured. Both near-field and far-field characteristics of the beam-refracting metasurface are investigated by simulations and measurements, which indicate that the proposed Huygens metasurface performs well in controlling electromagnetic waves

Construction of Lines of Constant Density and Constant Refractive Index for Ternary Liquid Mixtures.

Science.gov (United States)

Tasic, Aleksandar Z.; Djordjevic, Bojan D.

1983-01-01

Demonstrates construction of density constant and refractive index constant lines in triangular coordinate system on basis of systematic experimental determinations of density and refractive index for both homogeneous (single-phase) ternary liquid mixtures (of known composition) and the corresponding binary compositions. Background information,…

Refraction corrected calibration for aquatic locomotion research: application of Snell's law improves spatial accuracy

NARCIS (Netherlands)

Henrion, S.; Spoor, C.W.; Pieters, R.P.M.; Müller, U.K.; Leeuwen, van J.L.

2015-01-01

Images of underwater objects are distorted by refraction at the water–glass–air interfaces and these distortions can lead to substantial errors when reconstructing the objects' position and shape. So far, aquatic locomotion studies have minimized refraction in their experimental setups and used the

Automation, Operation, and Data Analysis in the Cryogenic, High Accuracy, Refraction Measuring System (CHARMS)

Science.gov (United States)

Frey, Bradley J.; Leviton, Douglas B.

2005-01-01

The Cryogenic High Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center has been enhanced in a number of ways in the last year to allow the system to accurately collect refracted beam deviation readings automatically over a range of temperatures from 15 K to well beyond room temperature with high sampling density in both wavelength and temperature. The engineering details which make this possible are presented. The methods by which the most accurate angular measurements are made and the corresponding data reduction methods used to reduce thousands of observed angles to a handful of refractive index values are also discussed.

Finite element approximation of the radiative transport equation in a medium with piece-wise constant refractive index

International Nuclear Information System (INIS)

Lehtikangas, O.; Tarvainen, T.; Kim, A.D.; Arridge, S.R.

2015-01-01

The radiative transport equation can be used as a light transport model in a medium with scattering particles, such as biological tissues. In the radiative transport equation, the refractive index is assumed to be constant within the medium. However, in biomedical media, changes in the refractive index can occur between different tissue types. In this work, light propagation in a medium with piece-wise constant refractive index is considered. Light propagation in each sub-domain with a constant refractive index is modeled using the radiative transport equation and the equations are coupled using boundary conditions describing Fresnel reflection and refraction phenomena on the interfaces between the sub-domains. The resulting coupled system of radiative transport equations is numerically solved using a finite element method. The approach is tested with simulations. The results show that this coupled system describes light propagation accurately through comparison with the Monte Carlo method. It is also shown that neglecting the internal changes of the refractive index can lead to erroneous boundary measurements of scattered light

Refractive Index Imaging of Cells with Variable-Angle Near-Total Internal Reflection (TIR) Microscopy.

Science.gov (United States)

Bohannon, Kevin P; Holz, Ronald W; Axelrod, Daniel

2017-10-01

The refractive index in the interior of single cells affects the evanescent field depth in quantitative studies using total internal reflection (TIR) fluorescence, but often that index is not well known. We here present method to measure and spatially map the absolute index of refraction in a microscopic sample, by imaging a collimated light beam reflected from the substrate/buffer/cell interference at variable angles of incidence. Above the TIR critical angle (which is a strong function of refractive index), the reflection is 100%, but in the immediate sub-critical angle zone, the reflection intensity is a very strong ascending function of incidence angle. By analyzing the angular position of that edge at each location in the field of view, the local refractive index can be estimated. In addition, by analyzing the steepness of the edge, the distance-to-substrate can be determined. We apply the technique to liquid calibration samples, silica beads, cultured Chinese hamster ovary cells, and primary culture chromaffin cells. The optical technique suffers from decremented lateral resolution, scattering, and interference artifacts. However, it still provides reasonable results for both refractive index (~1.38) and for distance-to-substrate (~150 nm) for the cells, as well as a lateral resolution to about 1 µm.

Antisymmetric-Symmetric Mode Conversion of Ultrasonic Lamb Waves and Negative Refraction on Thin Steel Plate

International Nuclear Information System (INIS)

Kim, Young H.; Sung, Jin Woo

2013-01-01

In this study, focusing of ultrasonic Lamb wave by negative refraction with mode conversion from antisymmetric to symmetric mode was investigated. When a wave propagates backward by negative refraction, the energy flux is antiparallel to the phase velocity. Backward propagation of Lamb wave is quite well known, but the behavior of backward Lamb wave at an interface has rarely been investigated. A pin-type transducer is used to detect Lamb wave propagating on a steel plate with a step change in thickness. Conversion from forward to backward propagating mode leads to negative refraction and thus wave focusing. By comparing the amplitudes of received Lamb waves at a specific frequency measured at different distance between transmitter and interface, the focusing of Lamb wave due to negative refraction was confirmed.

Refractive results of cataract surgery using optical biometry and Haigis formula in eyes with refractive keratotomy

Directory of Open Access Journals (Sweden)

Juan Carlos Sánchez Caballero

2013-04-01

Full Text Available OBJECTIVE: To analyze refractive results in postoperative cataract surgery in eyes previously submitted to keratotomy using Haigis formula and data provided by IOL Master®optical biometer. METHODS: The measurements for IOL calculation were obtained through optical biometry by partial coherence interferometry (IOL Master®- Zeiss, 5.4 and 5.5 version that provides us with the axial length, the central keratometry of 2.5mm, white-to-white diameter and anterior chamber anatomical depth. The formula chosen was Haigis. The surgical technique applied was with the scleral incision at 1.5 mm from the limbus, with scleral-corneal tunnel of 2.2 mm wide, phacoemulsification using INFINITI Ozil®- Alcon and implantation of hydrophobic acrylic aspheric intraocular lens - SN60WF®- Alcon. RESULTS: We studied 20 eyes submitted to keratotomy in the past and currently with cataract with indication for cataract surgerywith intraocular lens implantation using phacoemulsification. Postoperative spherical equivalent was plano in 40% of the eyes and lower than -1.00 in 85% of the eyes. CONCLUSION: The optical biometry by partial coherence interferometry associated with Haigis formula is a valid alternative in IOL calculation for eyes submitted to keratotomy. The refractive results are highly predictable and reproducible.

Relationship between visual field progression and baseline refraction in primary open-angle glaucoma.

Science.gov (United States)

Naito, Tomoko; Yoshikawa, Keiji; Mizoue, Shiro; Nanno, Mami; Kimura, Tairo; Suzumura, Hirotaka; Umeda, Yuzo; Shiraga, Fumio

2016-01-01

To analyze the relationship between visual field (VF) progression and baseline refraction in Japanese patients with primary open-angle glaucoma (POAG) including normal-tension glaucoma. In this retrospective study, the subjects were patients with POAG who had undergone VF tests at least ten times with a Humphrey Field Analyzer (Swedish interactive thresholding algorithm standard, Central 30-2 program). VF progression was defined as a significantly negative value of mean deviation (MD) slope at the final VF test. Multivariate logistic regression models were applied to detect an association between MD slope deterioration and baseline refraction. A total of 156 eyes of 156 patients were included in this analysis. Significant deterioration of MD slope was observed in 70 eyes of 70 patients (44.9%), whereas no significant deterioration was evident in 86 eyes of 86 patients (55.1%). The eyes with VF progression had significantly higher baseline refraction compared to those without apparent VF progression (-1.9±3.8 diopter [D] vs -3.5±3.4 D, P=0.0048) (mean ± standard deviation). When subject eyes were classified into four groups by the level of baseline refraction applying spherical equivalent (SE): no myopia (SE > -1D), mild myopia (-1D ≥ SE > -3D), moderate myopia (-3D ≥ SE > -6D), and severe myopia (-6D ≥ SE), the Cochran-Armitage trend analysis showed a decreasing trend in the proportion of MD slope deterioration with increasing severity of myopia (P=0.0002). The multivariate analysis revealed that baseline refraction (P=0.0108, odds ratio [OR]: 1.13, 95% confidence interval [CI]: 1.03-1.25) and intraocular pressure reduction rate (P=0.0150, OR: 0.97, 95% CI: 0.94-0.99) had a significant association with MD slope deterioration. In the current analysis of Japanese patients with POAG, baseline refraction was a factor significantly associated with MD slope deterioration as well as intraocular pressure reduction rate. When baseline refraction was classified into

Rectification of light refraction in curved waveguide arrays

OpenAIRE

Longhi, S.

2010-01-01

An 'optical ratchet' for discretized light in photonic lattices, which enables to observe rectification of light refraction at any input beam conditions, is theoretically presented, and a possible experimental implementation based on periodically-curved zigzag waveguide arrays is proposed.

Densities, excess molar volumes, and refractive indices of 1,1,2,2-tetrabromoethane and 1-alkanols binary mixtures

International Nuclear Information System (INIS)

Al-Hayan, M.N.M.; Al-Bader, Maher A.M.

2006-01-01

Densities, excess molar volumes, refractive indices, and changes in refractive index on mixing for (1,1,2,2-tetrabromoethane + 1-pentanol, or 1-hexanol, or 1-heptanol, or 1-octanol, or 1-decanol) have been determined at T = 293.15 K and at T = 303.15 K. The excess molar volumes and changes in refractive index have been fitted to Redlich-Kister polynomials. The effect of the chain length of the 1-alkanol on the excess molar volume and the change in the refractive index of its mixtures with 1,1,2,2-tetrabromoethane are discussed. In addition, the refractive indices are compared with calculated values using mixing rules proposed by several authors, and a good agreement is obtained

Densities, excess molar volumes, and refractive indices of 1,1,2,2-tetrachloroethane and 1-alkanols binary mixtures

International Nuclear Information System (INIS)

Al-Hayan, M.N.M.

2006-01-01

Densities, excess molar volumes, refractive indices, and changes in refractive index on mixing for 1,1,2,2-tetrachloroethane + 1-pentanol, or 1-hexanol, or 1-heptanol, or 1-octanol, or 1-decanol have been determined at T = (293.15 and 303.15) K. The excess molar volumes and changes in refractive index have been fitted to Redlich-Kister polynomials. The effect of the chain length of the 1-alkanol on the excess molar volume and the change in the refractive index of its mixtures with 1,1,2,2-tetrachloroethane was discussed. In addition, the refractive indices were compared with calculated values using mixing rules proposed by several authors, and a very good agreement was obtained

Aero-Optical Wavefront Propagation and Refractive Fluid Interfaces in Large-Reynolds-Number Compressible Turbulent Flows

National Research Council Canada - National Science Library

Catrakis, Haris J; Jefferies, Rhett

2005-01-01

... of the refractive field and interfaces. Direct, non-intrusive, and non-integrated imaging of the refractive index field in purely gaseous flows is achieved using laser induced fluorescence of acetone vapor molecularly premixed in air...

A search for refraction in the Kepler gas giant data set

Science.gov (United States)

Sheets, Holly A.; Jacob, Laurent; Cowan, Nicolas; Deming, Drake

2018-06-01

I present the results of our systematic search for refraction in the atmospheres of giant planets in the Kepler data set. We chose our candidates using the approximations of Sidis and Sari (ApJ, 2010, 720, 904S), selecting those that had an expected signal greater than 10 parts per million. We model the refraction shoulders as simple exponentials outside of transit and fit a transit+shoulder model to individual candidates. We find that the effect is not present to the extent predicted from the approximations.

Improvement of optical imaging resolution by a negative refraction photonic crystal with a solid immersion lens

International Nuclear Information System (INIS)

Tseng, M.-C.; Chen, L.-W.; Liu, C.-Y.

2008-01-01

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the solid immersion lens (SIL) technology in imaging system based on negative refraction PCs and analyzed the influence of refractive index and geometric parameters of SIL on imaging resolution. In the finite element method calculation, the resolution of our optical system has improved greatly. The high performance of imaging resolution was achieved with shorter radius and larger refractive index of SIL. Furthermore, the effects of the three kinds of SILs at the same radius were analyzed. Such a mechanism of negative refraction PCs and SILs should open up a new application for designing components in optical imaging systems

Negative Refraction in Rare-Earth Doped Crystals

Science.gov (United States)

2016-06-09

in the material, which in turn refracts into free- space. The false- color plots in Fig. 10 show the snapshots for the electric field in the two spatial...M. Shelby, Homogeneous Line Broadening of Optical Transitions of Ions and Molecules in Glasses, J. Lumin. 36, 179 (1987). [20] B. S. Ham , P. R

Roughened glass slides and a spectrophotometer for the detection of the wavelength-dependent refractive index of transparent liquids.

Science.gov (United States)

Niskanen, Ilpo; Räty, Jukka; Myllylä, Risto; Sutinen, Veijo; Matsuda, Kiyofumi; Homma, Kazuhiro; Silfsten, Pertti; Peiponen, Kai-Erik

2012-07-01

We describe a method to determine the wavelength-dependent refractive index of liquids by measurement of light transmittance with a spectrophotometer. The method is based on using roughened glass slides with different a priori known refractive indices and immersing the slides into the transparent liquid with unknown refractive index. Using the dispersion data on the glass material it is possible to find the index match between the liquid and the glass slide, and hence the refractive index of the liquid.

High-precision diode-laser-based temperature measurement for air refractive index compensation.

Science.gov (United States)

Hieta, Tuomas; Merimaa, Mikko; Vainio, Markku; Seppä, Jeremias; Lassila, Antti

2011-11-01

We present a laser-based system to measure the refractive index of air over a long path length. In optical distance measurements, it is essential to know the refractive index of air with high accuracy. Commonly, the refractive index of air is calculated from the properties of the ambient air using either Ciddor or Edlén equations, where the dominant uncertainty component is in most cases the air temperature. The method developed in this work utilizes direct absorption spectroscopy of oxygen to measure the average temperature of air and of water vapor to measure relative humidity. The method allows measurement of temperature and humidity over the same beam path as in optical distance measurement, providing spatially well-matching data. Indoor and outdoor measurements demonstrate the effectiveness of the method. In particular, we demonstrate an effective compensation of the refractive index of air in an interferometric length measurement at a time-variant and spatially nonhomogeneous temperature over a long time period. Further, we were able to demonstrate 7 mK RMS noise over a 67 m path length using a 120 s sample time. To our knowledge, this is the best temperature precision reported for a spectroscopic temperature measurement. © 2011 Optical Society of America

Highly sensitive refractive index fiber inline Mach-Zehnder interferometer fabricated by femtosecond laser micromachining and chemical etching

Science.gov (United States)

Sun, Xiao-Yan; Chu, Dong-Kai; Dong, Xin-Ran; Zhou, Chu; Li, Hai-Tao; Luo-Zhi; Hu, You-Wang; Zhou, Jian-Ying; Cong-Wang; Duan, Ji-An

2016-03-01

A High sensitive refractive index (RI) sensor based on Mach-Zehnder interferometer (MZI) in a conventional single-mode optical fiber is proposed, which is fabricated by femtosecond laser transversal-scanning inscription method and chemical etching. A rectangular cavity structure is formed in part of fiber core and cladding interface. The MZI sensor shows excellent refractive index sensitivity and linearity, which exhibits an extremely high RI sensitivity of -17197 nm/RIU (refractive index unit) with the linearity of 0.9996 within the refractive index range of 1.3371-1.3407. The experimental results are consistent with theoretical analysis.

Determination of the refractive index of glucose-ethanol-water mixtures using spectroscopic refractometry near the critical angle.

Science.gov (United States)

Sobral, H; Peña-Gomar, M

2015-10-01

A spectroscopic refractometer was used to investigate the dispersion curves of ethanol and D-glucose solutions in water near the critical angle; here, the reflectivity was measured using a white source. Dispersion curves were obtained in the 320-1000 nm wavelength range with a resolution better than 10(-4) for the refractive index, n. The differential refractive index is measured as a function of wavelength, and a simple expression is proposed to obtain the refractive index of the glucose-ethanol-water ternary system. Using this expression, combined with the experimental differential refractive index values, the concentrations of individual components can be calculated.

Interconnection between several eye biomechanical and biometric parameters in children with axial and refractive mild myopia

Directory of Open Access Journals (Sweden)

T. Ye. Tsybulskaya

2016-08-01

Full Text Available Aim – to study the relationship of biometric and biomechanical indicators of corneoscleral capsule of the eye in children with axial and refractive mild myopia. Materials and methods. Axial myopia was diagnosed in 32 children (64 eyes, refractive myopia – 18 (36 eyes. The control group – 16 children without ophthalmic diseases (32 eyes. Eye examination: visometry, automated refractometry, biomicroscopy, ophthalmoscopy, determination of the axial length of the eyeball and corneal hysteresis. Results. Significant differences were determined in the indicators of dioptric power of the cornea: 42.2 dpt in patients with axial and 44.7 dpt with refractive myopia (p<0.05, and also difference between patients with refractive myopia and the control group, in which the diopter power of cornea was 42.6 (p<0.05. There are also significant differences in the indicators of the axial length of eyes between axial and refractive myopia – 24.5±0.64 mm and 23.1±0.43 mm (p<0.05. Significant difference with the control group in the axial length marked only in eyes with axial myopia 22.7±0.33 mm and 24.5±0.64 mm, respectively (p<0.05. Corneal hysteresis determined significantly reduced on eyes with both the axial and refractive myopia, which was significantly lower than in the indicators of emmetropic eyes of the control group 13.7 (p<0.05. Corneal hysteresis is inversely related to the axial length of the eyeball: in patients with axial myopia r -0.32, p<0.05; with refractive myopia r -0.36, p<0.05. Сorrelation between diopter power of cornea and axial length of the eyeball: r -0.53, р<0.05 in eyes with axial myopia and r -0.42, p<0.05 refractive myopia. Comparative analysis showed no significant differences between the corneal hysteresis, the axial length of the eye and the spherical component of myopia. Conclusions. In patients with axial and refractive mild myopia corneal hysteresis is reduced on average in 1.2 and 1.1 times, in comparison with

Determination of femtosecond-laser-induced refractive-index changes in an optical fiber from far-field measurements

DEFF Research Database (Denmark)

Savolainen, Juha-Matti; Grüner-Nielsen, Lars; Kristensen, Poul

2014-01-01

A new method for direct writing of localized, circularly symmetric refractive-index changes in optical fibers with a femtosecond laser is demonstrated. The refractive-index changes are characterized using a novel approach employing comparison of numerical simulations to the measured far......-field profiles of unmodified and modified fibers. From the analysis, a negative refractive-index change of −0.015 0.005 within a radius of 0.6 0.1 μm is determined....

Influence of corneal asphericity on the refractive outcome of intraocular lens implantation in cataract surgery.

Science.gov (United States)

Savini, Giacomo; Hoffer, Kenneth J; Barboni, Piero

2015-04-01

To evaluate the possible influence of anterior corneal surface asphericity on the refractive outcomes in eyes having intraocular lens (IOL) implantation after cataract surgery. Fondazione G.B. Bietti IRCCS, Rome, Italy. Retrospective comparative case series. Intraocular lens power was calculated using the Haigis, Hoffer Q, Holladay 1, and SRK/T formulas. Asphericity (Q-value) was measured at 8.0 mm with a Placido-disk corneal topographer (Keratron), a rotating Scheimpflug camera (Pentacam), and a rotating Scheimpflug camera combined with Placido-disk corneal topography (Sirius). The relationship between the error in refraction prediction (ie, difference between expected refraction and refraction measured 1 month after surgery) and the Q-value was assessed by linear regression. The same IOL model (Acrysof SA60AT) was implanted in 115 eyes of 115 consecutive patients. Regression analysis showed a statistically significant relationship between the error in refraction prediction and the Q-value with all formulas and all devices. In all cases, a more negative Q-value (prolate cornea) was associated with a myopic outcome, whereas a more positive Q-value (oblate cornea) was associated with a hyperopic outcome. The highest coefficient of determination was detected between the Hoffer Q formula and the Placido-disk corneal topographer (R(2) = 0.2630), for which the error in refraction prediction (y) was related to the Q-value (x) according to the formula y = -0.2641 + 1.4589 × x. Corneal asphericity influences the refractive outcomes of IOL implantation and should be taken into consideration when using third-generation IOL power formulas. Dr. Hoffer receives book royalties from Slack, Inc., Thorofare, New Jersey, and formula royalties from all manufacturers using the Hoffer Q formula. No other author has a financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Probing a Possible Vacuum Refractive Index with Gamma-Ray Telescopes

CERN Document Server

Ellis, John; Nanopoulos, D V; PH-TH

2009-01-01

We have used a stringy model of quantum space-time foam to suggest that the vacuum may exhibit a non-trivial refractive index depending linearly on gamma-ray energy: eta -1 ~ E_gamma/M_QG1, where M_QG1 is some mass scale typical of quantum gravity that may be ~ 10^18 GeV: see Phys. Lett. B 665, 412 (2008) and references therein. The MAGIC, HESS and Fermi gamma-ray telescopes have recently probed the possible existence of such an energy-dependent vacuum refractive index. All find indications of time-lags for higher-energy photons, but cannot exclude the possibility that they are due to intrinsic delays at the sources. However, the MAGIC and HESS observations of time-lags in emissions from AGNs Mkn 501 and PKS 2155-304 are compatible with each other and a refractive index depending linearly on the gamma-ray energy, with M_QG1 ~ 10^18 GeV. We combine their results to estimate the time-lag Delta t to be expected for the highest-energy photon from GRB 080916c measured by the Fermi telescope, which has an energy ~ ...

Estimated refractive index and solid density of DT, with application to hollow-microsphere laser targets

International Nuclear Information System (INIS)

Briggs, C.K.; Tsugawa, R.T.; Hendricks, C.D.; Souers, P.C.

1975-01-01

The literature values for the 0.55-μm refractive index N of liquid and gaseous H 2 and D 2 are combined to yield the equation (N - 1) = [(3.15 +- 0.12) x 10 -6 ]rho, where rho is the density in moles per cubic meter. This equation can be extrapolated to 300 0 K for use on DT in solid, liquid, and gas phases. The equation is based on a review of solid-hydrogen densities measured in bulk and also by diffraction methods. By extrapolation, the estimated densities and 0.55-μm refractive indices for DT are given. Radiation-induced point defects could possibly cause optical absorption and a resulting increased refractive index in solid DT and T 2 . The effect of the DT refractive index in measuring glass and cryogenic DT laser targets is also described

Refractive index of r-cut sapphire under shock pressure range 5 to 65 GPa

International Nuclear Information System (INIS)

Cao, Xiuxia; Li, Jiabo; Li, Jun; Li, Xuhai; Xu, Liang; Wang, Yuan; Zhu, Wenjun; Meng, Chuanmin; Zhou, Xianming

2014-01-01

High-pressure refractive index of optical window materials not only can provide information on electronic polarizability and band-gap structure, but also is important for velocity correction in particle-velocity measurement with laser interferometers. In this work, the refractive index of r-cut sapphire window at 1550 nm wavelength was measured under shock pressures of 5–65 GPa. The refractive index (n) decreases linearly with increasing shock density (ρ) for shock stress above the Hugoniot elastic limit (HEL): n = 2.0485 (± 0.0197) − 0.0729 (± 0.0043)ρ, while n remains nearly a constant for elastic shocks. This behavior is attributed to the transition from elastic (below HEL) to heterogeneous plastic deformation (above HEL). Based on the obtained refractive index-density relationship, polarizability of the shocked sapphire was also obtained

Extrinsic fiber-optic Fabry-Perot interferometer sensor for refractive index measurement of optical glass

International Nuclear Information System (INIS)

Chen Jihuan; Zhao Jiarong; Huang Xuguang; Huang Zhenjian

2010-01-01

A simple fiber-optic sensor based on Fabry-Perot interference for refractive index measurement of optical glass is investigated both theoretically and experimentally. A broadband light source is coupled into an extrinsic fiber Fabry-Perot cavity formed by the surfaces of a sensing fiber end and the measured sample. The interference signals from the cavity are reflected back into the same fiber. The refractive index of the sample can be obtained by measuring the contrast of the interference fringes. The experimental data meet with the theoretical values very well. The proposed technique is a new method for glass refractive index measurement with a simple, solid, and compact structure.

Image distortion due to refraction by planar surfaces

Energy Technology Data Exchange (ETDEWEB)

Arizaga, R; Cap, N; Rabal, H; Trivi, M [Centro de Investigaciones Opticas (CONICET La Plata-CIC) and OPTIMO Dto de Ciencias Basicas, Fac. de Ingenieria UNLP, PO Box 3, 1897 Gonnet, La Plata (Argentina)

2010-01-15

The term 'apparent depth' is commonly treated in textbooks as an issue easily understandable from the point of view of paraxial optical geometrical optics. Nevertheless, everyday life tells us that most of the time the observation of objects immersed in water is made under a great range of visual angles where the paraxial approximation is not valid. Here we developed a non-paraxial treatment to calculate the position and shape of the image of objects immersed in liquids of different refractive indices. The approach was focused on the parametric positions of the images of a single point at different viewing angles. Then we calculated how the image of an extended object is distorted. By using the Matlab software, it is possible to visualize the images for different geometrical conditions. We also include the analysis for refractive index with negative values as is the case of metamaterials.

Refractive and diffractive scattering in the interstellar medium

International Nuclear Information System (INIS)

Cordes, J.M.; Pidwerbetsky, A.; Lovelace, R.V.E.

1986-01-01

Radio wave propagation through electron-density fluctuations in the ISM is studied. Observable propagation effects are explored using a one-dimensional thin-screen model for the turbulent medium. Diffraction caused by stochastic small-scale irregularities is combined with refraction from deterministic large-scale irregularities. Some of the effects are illustrated with numerical simulations of the wave propagation. Multiple imaging is considered, delineating the possible effects and discussing their extensions to two-dimensional screens and extended three-dimensional media. The case where refraction as well as diffraction is caused by a stochastic medium with a spectrum of a given form is considered. The magnitudes of observable effects is estimated for representative spectra that may be relevant to the ISM. The importance of the various effects for timing and scintillation observations of pulsars, VLBI observations of galactic and extragalactic radio sources, and for variability measurements of extragalactic sources is assessed. 47 references

Image distortion due to refraction by planar surfaces

International Nuclear Information System (INIS)

Arizaga, R; Cap, N; Rabal, H; Trivi, M

2010-01-01

The term 'apparent depth' is commonly treated in textbooks as an issue easily understandable from the point of view of paraxial optical geometrical optics. Nevertheless, everyday life tells us that most of the time the observation of objects immersed in water is made under a great range of visual angles where the paraxial approximation is not valid. Here we developed a non-paraxial treatment to calculate the position and shape of the image of objects immersed in liquids of different refractive indices. The approach was focused on the parametric positions of the images of a single point at different viewing angles. Then we calculated how the image of an extended object is distorted. By using the Matlab software, it is possible to visualize the images for different geometrical conditions. We also include the analysis for refractive index with negative values as is the case of metamaterials.

Optofluidic refractive index sensor based on partial reflection

Science.gov (United States)

Zhang, Lei; Zhang, Zhang; Wang, Yichuan; Ye, Meiying; Fang, Wei; Tong, Limin

2017-06-01

We demonstrate a novel optofluidic refractive index (RI) sensor with high sensitivity and wide dynamic range based on partial reflection. Benefited from the divergent incident light and the output fibers with different tilting angles, we have achieved highly sensitive RI sensing in a wide range from 1.33 to 1.37. To investigate the effectiveness of this sensor, we perform a measurement of RI with a resolution of ca. 5.0×10-5 refractive index unit (RIU) for ethylene glycol solutions. Also, we have measured a series of liquid solutions by using different output fibers, achieving a resolution of ca. 0.52 mg/mL for cane surge. The optofluidic RI sensor takes advantage of the high sensitivity, wide dynamic range, small footprint, and low sample consumption, as well as the efficient fluidic sample delivery, making it useful for applications in the food industry.

Refraction of Radio Waves on the Radio-Occultation Satellite-to-Satellite Paths as a Characteristic of the Atmospheric State

Science.gov (United States)

Matyugov, S. S.; Yakovlev, O. I.; Pavelyev, A. G.; Pavelyev, A. A.; Anufriev, V. A.

2017-10-01

We present the results of analyzing the radio-wave refractive characteristics measured on the radio-occultation paths between the GPS navigation satellites and the FORMOSAT-3 research satellites in the central region of the European territory of Russia in 2007-2013. The diurnal, seasonal, and annual variations in the refraction angle at altitudes of 2 to 25 km are discussed. It is shown that the refraction angle can be used as an independent characteristic of the atmospheric state and its long-term variation trends. Diurnal and nocturnal variations in the refraction angle in the winter and summer seasons are analyzed. Trends in the atmospheric refraction variations over seven years are discussed.

Direct characterization of ultraviolet-light-induced refractive index structures by scanning near-field optical microscopy

DEFF Research Database (Denmark)

Svalgaard, Mikael; Madsen, S.; Hvam, Jørn Märcher

1998-01-01

We have applied a reflection scanning near-field optical microscope to directly probe ultraviolet (UV)-light-induced refractive index structures in planar glass samples. This technique permits direct comparison between topography and refractive index changes (10(-5)-10(-3)) with submicrometer...

Computed tomography of x-ray index of refraction using the diffraction enhanced imaging method

International Nuclear Information System (INIS)

Dilmanian, F.A.; Ren, B.; Wu, X.Y.; Orion, I.; Zhong, Z.; Thomlinson, W.C.; Chapman, L.D.

2000-01-01

Diffraction enhanced imaging (DEI) is a new, synchrotron-based, x-ray radiography method that uses monochromatic, fan-shaped beams, with an analyser crystal positioned between the subject and the detector. The analyser allows the detection of only those x-rays transmitted by the subject that fall into the acceptance angle (central part of the rocking curve) of the monochromator/analyser system. As shown by Chapman et al , in addition to the x-ray attenuation, the method provides information on the out-of-plane angular deviation of x-rays. New images result in which the image contrast depends on the x-ray index of refraction and on the yield of small-angle scattering, respectively. We implemented DEI in the tomography mode at the National Synchrotron Light Source using 22 keV x-rays, and imaged a cylindrical acrylic phantom that included oil-filled, slanted channels. The resulting 'refraction CT image' shows the pure image of the out-of-plane gradient of the x-ray index of refraction. No image artefacts were present, indicating that the CT projection data were a consistent set. The 'refraction CT image' signal is linear with the gradient of the refractive index, and its value is equal to that expected. The method, at the energy used or higher, has the potential for use in clinical radiography and in industry. (author)

The refraction and reflection laws from a complete integral of the eikonal equation and Huygens’ principle

International Nuclear Information System (INIS)

Castro-Ramos, Jorge; Juárez-Reyes, Salvador Alejandro; Ortega-Vidals, Paula; Silva-Ortigoza, Gilberto; Suárez-Xique, Román; Marcelino-Aranda, Mariana; Silva-Ortigoza, Ramón

2015-01-01

In this work we assume that we have two given optical media with constant refraction indexes, which are separated by an arbitrary refracting surface. In one of the optical media we place a point light source at an arbitrary position. The aim of this work is to use a particular complete integral of the eikonal equation and Huygens’ principle to obtain the refraction and reflection laws. We remark that this complete integral associates a new point light source with each light ray that arrives at the refracting surface. This means that by using only this complete integral it is not possible to determine the direction of propagation of the refracted light rays; the direction of propagation is obtained by imposing two extra conditions on the complete integral which are equivalent to Huygens’ principle (in two dimensions, only one condition is needed). Finally, we establish the connection between the complete integral used here and that derived by using the k-function procedure introduced by Stavroudis, which works with plane wavefronts instead of spherical ones. (paper)

Improving axial resolution in confocal microscopy with new high refractive index mounting media.

Science.gov (United States)

Fouquet, Coralie; Gilles, Jean-François; Heck, Nicolas; Dos Santos, Marc; Schwartzmann, Richard; Cannaya, Vidjeacoumary; Morel, Marie-Pierre; Davidson, Robert Stephen; Trembleau, Alain; Bolte, Susanne

2015-01-01

Resolution, high signal intensity and elevated signal to noise ratio (SNR) are key issues for biologists who aim at studying the localisation of biological structures at the cellular and subcellular levels using confocal microscopy. The resolution required to separate sub-cellular biological structures is often near to the resolving power of the microscope. When optimally used, confocal microscopes may reach resolutions of 180 nm laterally and 500 nm axially, however, axial resolution in depth is often impaired by spherical aberration that may occur due to refractive index mismatches. Spherical aberration results in broadening of the point-spread function (PSF), a decrease in peak signal intensity when imaging in depth and a focal shift that leads to the distortion of the image along the z-axis and thus in a scaling error. In this study, we use the novel mounting medium CFM3 (Citifluor Ltd., UK) with a refractive index of 1.518 to minimize the effects of spherical aberration. This mounting medium is compatible with most common fluorochromes and fluorescent proteins. We compare its performance with established mounting media, harbouring refractive indices below 1.500, by estimating lateral and axial resolution with sub-resolution fluorescent beads. We show furthermore that the use of the high refractive index media renders the tissue transparent and improves considerably the axial resolution and imaging depth in immuno-labelled or fluorescent protein labelled fixed mouse brain tissue. We thus propose to use those novel high refractive index mounting media, whenever optimal axial resolution is required.

Improving axial resolution in confocal microscopy with new high refractive index mounting media.