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Ng, Siu-chun Danny, and 吳兆駿. "The prevalence of refractive error and visual impairment caused by uncorrected refractive error in China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B4804331X.
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Purpose: WHO reports 46% of world vision impairment from refractive error (RE)
among children occurs in China. We estimated RE prevalence and associated vision
impairment (VI) among Chinese children and adults.
Methods: Data from population-based studies were stratified by gender in age intervals
of 3 years (ages 3-17 y) or 10 years (ages >= 30 y): counts of persons with myopia
(worse eye spherical equivalent <= -1.0D, <= -2.0D, <= -6.0D) and prevalence of low
vision (< 6/12 in the better-seeing eye for children and < 6/18 for adults) and blindness
(<=6/60) attributable to RE. Figures for VI included persons with habitual vision below
the cutoff improving to above the cutoff with refraction, and those with myopic
retinopathy. Estimates for ages 18-29 y were obtained from regression models derived
from the pooled estimates. Prevalence of myopia and VI attributable to RE in each
age/gender category was calculated by applying modeled rates to 2000 China census
figures and projections for 2020. Association with VI attributable to RE was tested for:
gender, urban versus rural residence, and residence in provinces with per capita GDP in
the upper versus lower 50% for China.
Results: Data were obtained from 5 cohorts for children and 14 for adults. There were
291 million and 21.4 million persons with myopia <= -1.0D and <= -6.0D respectively in
2000, expected to rise to 306 million and 36.9 million by 2020. Of these, 18.4 million
were blind and 116 million had low vision in 2000, with figures of 25.3 million and 123
million in 2020. Children accounted for the following proportion of RE disease burden in
China in 2000: myopia <= -1.0D: 19.0%; RE-associated low vision: 56.1%; blindness:
14.1%. Refractive error was responsible for 82.3% of blindness and 90.5% of low vision
among children, and 11.6% and 64.4% of blindness and low vision among adults. Urban
residence (OR 1.85, P = 0.004) and higher GDP (OR 10.6, P < 0.001) were associated
with refractive blindness among children. For adults, lower GDP was associated with
refractive blindness (OR 1.47, P = 0.01). Gender was un-associated with refractive
blindness among children or adults.
Conclusions: Both children and adults suffer a heavy burden of VI associated with RE in
China. Income may affect risk for such VI differently among children and adults.published_or_final_version
Public Health
Master
Master of Public Health
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Feltham, Mark Hayes Optometry & Vision Science Faculty of Science UNSW. "Factors which affect refractive outcome following LASIK for myopia." Awarded by:University of New South Wales. School of Optometry and Vision Science, 2004. http://handle.unsw.edu.au/1959.4/20800.
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Purpose: To improve the predictability, accuracy and stability of laser in-situ keratomileusis (LASIK), by evaluating the clinical, procedural and tissue response factors that affect refractive outcomes. Methods: Myopic LASIK surgeries (n=5,978) were carried out using the Technolas planoscan and Nidek EC-5000 excimer lasers. Clinical variables associated with a refractive outcome of within ??0.50 D of the target were identified using regression analysis. Possible procedural variations such as the timing of the procedure and accuracy of both the chosen keratome and excimer laser were evaluated. The predictability and accuracy of the ablation was assessed by measuring changes in corneal thickness during and after the procedure. Factors influencing the stability of refractive outcome were assessed. Results: Clinical factors associated with a refractive outcome of within ??0.50 D of the target included; corrections less than 5.00 DS (OR 0.21x, 95% CI 0.11-0.40x compared with corrections over -5.00 DS[referent]), patients younger than 40 years (patients over 50 OR 8.27x, 95% CI 3.41-20.03x, patients 40 to 50 years OR 1.93x, 95% CI 0.96-3.90x, compared with patients under 40[referent]) and average pre-operative curvatures between 43.50 and 45.50D (OR 0.39x, 95% CI 0.18-0.83 compared with curvatures of less than 43.50D [referent]). Refractive stability was improved using optic zone sizes between 5.5-6.0 mm, reduced myopic corrections, flatter pre-operative corneal curvatures and thicker corneal flaps (R??=25%, p<0.001). Procedural factors associated with poorer outcomes included: thinner measured flap thickness, deeper ablations and the use of the automated corneal shaper (ACS) microkeratome with a novice surgical team (R??=34%, p < 0.001). Delaying the ablation from 20 to 90 seconds (s) after flap lift was associated with a more stable refractive outcome at three months (p=0.017). In the 90 s following flap lift, the cornea thinned by 5??3%. The ablation rate per scan varied between procedures, however, the effect on refractive outcome was small (r=0.15, p=0.267). Changes in central corneal thickness indicated refractive stability (p=0.039). Conclusions: Applying the optimal clinical and procedural factors as described afforded a refractive outcome in a further 8% of cases, resulting in 94% to 96% of cases within ??0.50 DS of target. Refractive predictability was limited due to the inability of the keratome to produce a consistent corneal flap thickness and unexpected changes in corneal thickness. The accuracy of refractive outcome will decrease with larger ablations. The degree of refractive inaccuracy with high refractive corrections (> -10.00 D) can be over 1.00 D.
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Ferraz, Fábio Henrique da Silva [UNESP]. "Perfil de distribuição de erros refracionais no sul do centro-oeste do estado de São Paulo e seu impacto na acuidade visual: estudo de base populacional. -." Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/105628.
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000741373.pdf: 4583650 bytes, checksum: 87f6f61f6501ebdd745502a6340efa62 (MD5)Determinar o perfil de distribuição dos erros refracionais em uma amostra populacional do centro-oeste do Estado de São Paulo, suas possíveis associações com características individuais e a influência sobre a acuidade visual. foi desenvolvido estudo de secção transversal com amostragem residencial probabilística e sistemática em nove municípios no sul do centro-oeste paulista, como parte do Projeto de Prevenção à Cegueira na Comunidade. Os indivíduos acima de um ano de idade foram submetidos a entrevista e exame oftalmológico completo. A acuidade visual em sistema Snellen e posterior conversão para logMAR foi obtida antes e após exame de refração e categorizada em quatro segmentos. Os erros refracionais foram classificados em miopia (EE ≤ - 0,50D), hipermetropia (EE ≥ 0,50D), astigmatismo (DC ≤ -0,50D) e anisometropia (diferença de EE ≥ 1,00D entre os olhos). Foi realizada a análise descritiva dos dados de prevalência na amostra, análise univariada e multivariada com modelos de regressão logística múltipla para determinar possíveis associações de prevalências. 3012 residências foram entrevistadas e 7654 indivíduos foram incluídos no estudo, sendo 62,7% mulheres, 92,1% considerados com pele branca e média para a idade de 36,89 anos (extremos de 1 a 96 anos). A miopia foi mais prevalente na terceira e quarta décadas de vida, atingindo 43,31% sem diferenças significativas entre sexos, enquanto a hipermetropia foi mais prevalente entre mulheres acima de 60 anos de idade, com uma frequência de 65,6% nesta faixa etária. O astigmatismo apresentou uma frequência progressivamente maior com a idade e semelhante entre os sexos. O eixo do astigmatismo também apresentou variação conforme a idade, com o eixo horizontal mais frequente em jovens e o vertical nos idosos. A prevalência da anisometropia apresentou variação com a idade sendo mais frequente nos extremos de idade,...
Establish the refractive errors distribution in a population sample of the Central São Paulo State, correlations with personal features and its influence in visual acuity. A cross sectional survey was developed with randomized and systematic residential sampling in nine cities of middle region of São Paulo St/Brazil as part of Blindness Prevention Project at Community. Inhabitants above one year old were submitted to an interview and full ophthalmic exam. Visual acuity in logMAR system was determined before and after refraction exam and classified in four categories. Refractive errors were classified in myopia (SE ≤ -0,50D), hyperopia (SE ≥ 0,50D), astigmatism (CD ≤ -0,50D) and anisometrophy (SE difference between eyes ≥ 1,00D). Prevalence data sample were submitted to descriptive analysis, univariate and multivariate logistic regression models to find eventual prevalence associations. 7654 participants were included in this survey, in which 62,7% were women, 92,1% with white skin and middle age of 36,89 years old (1 to 96 years). Myopia was more prevalent at 3rd and 4th decades, achieving 43,31% without significant differences between genders, while hyperopia was more prevalent in women above 60 years old, with 65,5%. Astigmatism prevalence increased by age with no differences between genders. Astigmatism axis changed by age too, when horizontal axis were more frequently observed in youngers and vertical in olders. Anisometrophy prevalence changed by age, more frequent at extremes, achieving 32,66% after 70 years old. No significant differences were found in ethnic categories. Visual acuity increasing prevalence by visual impairment corrected with spectacles (UREN) was 6,53% in the total sample, mainly after 60 years old and high refrective errors. Prevalence associations were found between age and all ametrophic categories, sex and hyperopia and between UREN with myopia, hyperopia and ...
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Ferraz, Fábio Henrique da Silva. "Perfil de distribuição de erros refracionais no sul do centro-oeste do estado de São Paulo e seu impacto na acuidade visual : estudo de base populacional. -." Botucatu, 2013. http://hdl.handle.net/11449/105628.
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Orientador: Silvana Artioli SchelliniBanca: Milton Ruiz Alves
Banca: Carlos Eduardo Leite Arieta
Banca: Maria Rosa Bet de Moraes Silva
Banca: Flávio Eduardo Hirai
Resumo: Determinar o perfil de distribuição dos erros refracionais em uma amostra populacional do centro-oeste do Estado de São Paulo, suas possíveis associações com características individuais e a influência sobre a acuidade visual. foi desenvolvido estudo de secção transversal com amostragem residencial probabilística e sistemática em nove municípios no sul do centro-oeste paulista, como parte do Projeto de Prevenção à Cegueira na Comunidade. Os indivíduos acima de um ano de idade foram submetidos a entrevista e exame oftalmológico completo. A acuidade visual em sistema Snellen e posterior conversão para logMAR foi obtida antes e após exame de refração e categorizada em quatro segmentos. Os erros refracionais foram classificados em miopia (EE ≤ - 0,50D), hipermetropia (EE ≥ 0,50D), astigmatismo (DC ≤ -0,50D) e anisometropia (diferença de EE ≥ 1,00D entre os olhos). Foi realizada a análise descritiva dos dados de prevalência na amostra, análise univariada e multivariada com modelos de regressão logística múltipla para determinar possíveis associações de prevalências. 3012 residências foram entrevistadas e 7654 indivíduos foram incluídos no estudo, sendo 62,7% mulheres, 92,1% considerados com pele branca e média para a idade de 36,89 anos (extremos de 1 a 96 anos). A miopia foi mais prevalente na terceira e quarta décadas de vida, atingindo 43,31% sem diferenças significativas entre sexos, enquanto a hipermetropia foi mais prevalente entre mulheres acima de 60 anos de idade, com uma frequência de 65,6% nesta faixa etária. O astigmatismo apresentou uma frequência progressivamente maior com a idade e semelhante entre os sexos. O eixo do astigmatismo também apresentou variação conforme a idade, com o eixo horizontal mais frequente em jovens e o vertical nos idosos. A prevalência da anisometropia apresentou variação com a idade sendo mais frequente nos extremos de idade, ...
Abstract: Establish the refractive errors distribution in a population sample of the Central São Paulo State, correlations with personal features and its influence in visual acuity. A cross sectional survey was developed with randomized and systematic residential sampling in nine cities of middle region of São Paulo St/Brazil as part of Blindness Prevention Project at Community. Inhabitants above one year old were submitted to an interview and full ophthalmic exam. Visual acuity in logMAR system was determined before and after refraction exam and classified in four categories. Refractive errors were classified in myopia (SE ≤ -0,50D), hyperopia (SE ≥ 0,50D), astigmatism (CD ≤ -0,50D) and anisometrophy (SE difference between eyes ≥ 1,00D). Prevalence data sample were submitted to descriptive analysis, univariate and multivariate logistic regression models to find eventual prevalence associations. 7654 participants were included in this survey, in which 62,7% were women, 92,1% with white skin and middle age of 36,89 years old (1 to 96 years). Myopia was more prevalent at 3rd and 4th decades, achieving 43,31% without significant differences between genders, while hyperopia was more prevalent in women above 60 years old, with 65,5%. Astigmatism prevalence increased by age with no differences between genders. Astigmatism axis changed by age too, when horizontal axis were more frequently observed in youngers and vertical in olders. Anisometrophy prevalence changed by age, more frequent at extremes, achieving 32,66% after 70 years old. No significant differences were found in ethnic categories. Visual acuity increasing prevalence by visual impairment corrected with spectacles (UREN) was 6,53% in the total sample, mainly after 60 years old and high refrective errors. Prevalence associations were found between age and all ametrophic categories, sex and hyperopia and between UREN with myopia, hyperopia and ...
Doutor
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Webber, Fiona. "A study of the prevalence of refractive errors and of patients requring refractive services at 15 eye clinics in the Amathole, Chris Hani, Joe Gqabi and O. R. Tambo districts of the Eastern Cape." Thesis, University of Fort Hare, 2012. http://hdl.handle.net/10353/d1001100.
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This is a study on the prevalence of refractive errors and patients requiring refractive services at 15 eye clinics in the Amathole, Chris Hani, Joe Gqabi and OR Tambo District Municipalities of the Eastern Cape. This is an area characterised by extreme poverty where the cost of an eye examination and prescription spectacles remains financially unobtainable for most. Optometry services are provided mainly by private optometrists who service the small proportion of the population that can afford them. Adults and children remain house bound or are labelled as dull and unproductive simply because they don’t have access to an eye examination and a pair of spectacles. Purpose The purpose of the study is to identify patients with refractive errors and those requiring refractive services at the 15 eye clinics in the Eastern Cape. Another purpose is to describe the refractive services that are available to patients attending health facilities, where the eye clinics are conducted. Lastly, the purpose is to explore the possibility of nurses providing refractive services independently or under the supervision of optometrists to supplement the lack to refracting and dispensing services. Study Method A quantitative and qualitative non-experimental descriptive design was used. Research involved the analysis of Vision Care’s eye clinic records collected from 15 eye clinics from January 2010-June 2010. Semi-structured interviews were conducted with 30 nurses working at the 15 health facilities where the eye clinics were conducted using purposive sampling. The quantitative data was analysed using excel spreadsheets and graphs and qualitative data was analysed using coding and categorizing methods. Conclusion According to Vision Care’s data of the patients assessed, 19.2 percent had a refractive error and 54 percent of the patients required refractive services. It is estimated that 71.41 percent of the patients had a refractive error according to the optometrist. Although there were some organisations active in the eradication of cataracts, there was little healthcare available in the form of refraction services. xiv Patients needed to travel an average of 63.8kms to access refraction services against the backdrop of poor roads, poverty and unemployment. 28 out of 30 nurses either ‘strongly agreed’ or ‘agreed’ that nurses could be trained to perform refractions and dispense spectacles. 29 out of 30 nurses thought that this would have a positive impact on eye care. Further research is necessary to assess the feasibility of implementing a nurse operated refractive program and whether it should be within their scope of practice to refract and dispense spectacles.
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Tayah, David. "Componentes oculares em anisometropia." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/5/5149/tde-10032008-153020/.
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Objetivo: Em anisométropes, comparar os valores médios individuais dos componentes oculares de ambos os olhos (poder da córnea, profundidade da câmara anterior, poder equivalente do cristalino e comprimento axial), correlacionar as diferenças dos componentes oculares com as diferenças de refração de ambos os olhos; verificar a contribuição total e a seqüência geral de influência das variáveis na diferença refrativa; e identificar o menor número de fatores que contenham o mesmo grau de informações expressas no conjunto de variáveis que influenciam na diferença refrativa. Métodos: Realizou-se um estudo transversal analítico em população de 77 anisométropes de duas ou mais dioptrias, atendida no ambulatório de Oftalmologia do Hospital Universitário da Faculdade de Medicina Nilton Lins, Manaus, Amazonas. Os anisométropes foram submetidos à refração estática objetiva e subjetiva, ceratometria e biometria ultra-sônica A-scan. A análise dos dados foi feita por meio dos seguintes modelos estatísticos: análise univariada, multivariada, de regressão múltipla e fatorial. Resultados: 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) (P<0,01) e correlação negativa fraca entre a diferença refrativa e a diferença de poder do cristalino (r=-0,34) (p<0,01). As variáveis analisadas responderam, no seu conjunto, por 78% da variação total para a diferença refrativa. A seqüência geral de influência das variáveis na diferença refrativa foi a seguinte: comprimento axial, poder do cristalino, poder da córnea e profundidade da câmara anterior. Foram identificados três fatores para a diferença refrativa: a) fator 1 (refração, comprimento axial); b) fator 2 (profundidade da câmera anterior, poder da córnea) e c) fator 3 (poder do cristalino). Conclusões: O estudo conduzido em 77 indivíduos com anisometropias variando de 2,00 a mais de 19,00 dioptrias, realizado para avaliar a influência dos componentes oculares, mostrou que o comprimento axial foi o principal fator causador das anisometropias, seguido pelo cristalino que contribuiu menos, depois pela córnea e profundidade da câmara anterior, com contribuições ainda menores. A investigação sugere falência no mecanismo adaptativo normal em anisometropia, o que poderia produzir não só descontrole do alongamento do comprimento axial (fator 1), mas também falência no controle do aplanamento da córnea e do aprofundamento da câmara anterior (fator 2) e no achatamento do cristalino (fator 3).Purpose: To compare the individual means of ocular components of both eyes (corneal power, anterior chamber depth, crystalline lens power and axial length) in patients with anisometropia; to correlate the differences of the ocular components with refractive differences in both eyes; to verify total contribution and the sequence of influence that variables have in 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, Medical School Nilton Lins, Manaus, Amazon state. All participants were submitted to ophthalmologic exam which included objective and subjective cycloplegic refractometry, keratometry and ultrasonic biometry. Data analysis comprised the following statistical models: univariate, multivariate, multiple and factorial regression analyses. Results: There were no significant differences in the comparison of the individual means of the ocular components. There was negative correlation between refractive difference and difference of axial length (r=- 0.64; p<0.01) and weak negative correlation between refractive difference and crystalline lens power difference (r=-0.34; p< 0.01). The analyzed variables amounted to 78% of the total variation of refractive difference. The general sequence of variables influencing refractive difference was: axial length, crystalline lens power, cornea power, and anterior chamber depth. There were three factors identified for refractive differences: a) factor 1 (refraction, axial length); b) factor 2 (anterior chamber depth, cornea power), and c) factor 3 (crystalline lens power). Conclusions: Seventy-seven cases of anisometropia ranging from 2,00 to over 19,00 dioptres, examined for the individual components of refraction, showed that axial length was the major causative factor; crystalline lens have contributed less, followed by cornea and anterior chamber length. This study has suggested deficit of the normal adaptive mechanism in anisometropia that could produce not only axial elongation (factor 1), but also failure to control flattening of the cornea, deepening of the anterior chamber length (factor 2) and flattening of crystalline lens (factor 3).
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Běťáková, Vendula. "Design optometrického přístroje pro primární vyšetření zraku." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318744.
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The goal of this bachelor thesis is a proposal design of optometric device for primary examination of eye vision, which should respect the functional requirements and conceptualize the technical and aesthetic aspects. The work includes a study of the current market situation and development of new technologies in the field. The proposal deals with an ergonomic design and issues.
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Beverage, Jacob Lee. "Measuring refractive error in the human eye using a Shack-Hartmann-based autorefractor." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/298729.
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The oldest and most prevalent optical system in the world is the human eye. Variations in the anatomical structure of the eye can cause errors in its optical performance, which in turn lead to errors in the overall performance of the visual system. Fortunately, these refractive errors can be measured and then corrected externally with spectacles, contact lenses, or refractive surgery. This dissertation describes the design, fabrication, and testing of a new autorefractor that can be used to objectively measure human refractive error. The new autorefractor is based on Shack-Hartmann wavefront sensing techniques and uses a novel, Fourier transform-based algorithm to estimate refractive error. The Fourier-based data analysis models the wavefront aberration as a combination of defocus and astigmatism only, expresses the simplified wavefront in terms of measurable quantities in Fourier-space, and relates the coefficients describing the wavefront to the patient's refraction. The Shack-Hartmann-based autorefractor (SHAR) is designed to be inexpensive and compact to facilitate its transition to a commercial device. It represents a significant improvement in automated clinical refraction because it can make accurate measurements of a wide range of refractive errors without relying on moving parts or the intensity of light reflected off the retina. To evaluate its performance, the SHAR was compared to the gold-standard among current commercially available autorefractors in a study of human refractive errors. The results from this limited study population suggested that the SHAR has the potential to perform at least as well as the commercial standard autorefractor.
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Orr, Janis B. "Optical and biometric characteristics of the eye and their relationship to refractive error." Thesis, Glasgow Caledonian University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601635.
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Refractive error, particularly myopia, is a significant visual problem considered to result from a complex interplay between genetics and environmental influences. While there has been a worldwide increase in the prevalence of myopia in recent years, the aetiology of myopia is not yet known. Emmetropisation is the process of normal eye growth during development such that refractive error stabilises at, or close to, emmetropia. This has been shown to be an active process influenced by the visual environment. Previous animal studies have shown that emmetropisation can be disrupted by introducing abnormal optical factors into the central and/or peripheral visual field. Differences in the optical and biometric properties of the emmetropic, myopic, and hyperopic eye have previously been found. The aim of this thesis was to extend previous work by investigating several important biometric and optical characteristics, in emmetropic, myopic and hyperopic eyes, in order to establish any systematic refractive group differences, which may explain the failure of the emmetropisation process. The results presented in this thesis show clear differences between the shape and refractive characteristics of the peripheral retina between myopic, emmetropic and hyperopic subjects. These results suggest that refractive error group dependent differences in the peripheral retina could be a key correlate of refractive error development. Optical properties of the eye, specifically pupil diameter, monochromatic higher order aberrations, and chromatic aberration were shown not to vary significantly between refractive groups, suggesting that these factors are unlikely to play any major role in the development of myopia. It could be, however, that the optical properties of the eye are a consequence of myopia development. Alternatively, the optical properties of the eye vary before myopia develops, or reaches adult levels.
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Carnell, Peter Hamilton. "A finite element model for estimating mechanical properties of the cornea." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/17946.
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Schultz, Kristin E. "Accommodative microfluctuations, crystalline lens tension, ciliary body thickness, and refractive error in children." Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1240445960.
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Kuchem, Mallory Kuhlmann. "Ciliary muscle, eye shape, and accommodation in adults with anisometropia." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338254685.
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Nava, Diane Rachel. "Participation of retinal glucagonergic amacrine cells in the regulation of eye growth and refractive error| Evidence from neurotoxins and in vivo immunolesioning." Thesis, University of California, Berkeley, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10150995.
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Growth is one of the fundamental characteristics of biological systems. The study of eye growth regulation presents an interesting window that allows for the investigation of the role of the visual environment on internal processes. We now know that there is an intricate circuitry within the eye, independent of higher brain processes, that controls the growth of the eye but more needs to be elucidated about these local regulatory circuits. An improved understanding of this circuitry is critical to developing new therapies for abnormalities in eye growth regulation such as myopia, which is impacting more and more individuals around the world each day and in its more severe from, is linked to potentially blinding ocular complications.
The role of retinal glucagon, a neuropeptide, in the regulation of eye growth and refractive error has attracted the interest of researchers over the past 15 years yet there remain many unresolved questions. The research described in this dissertation aimed to elucidate the respective roles in eye growth regulation of specific subpopulations of retinal glucagonergic amacrine cells, which have been the subject of much speculation as the source of inhibitory growth signals, i.e. stop signals, yet not thoroughly investigated.
The approach taken to investigate this problem is to ablate glucagonergic amacrine cells in vivo using different neurotoxins, and to examine how this affects the sign-dependent circuitry of eye growth regulation. In addition, with the advent of advancements in high resolution imaging and electrophysiology, we were able to characterize the effects of these neurotoxins on the region-specific and time-sensitive changes in the structure and function of the living retina.
That the inhibitory response induced by imposed myopic defocus remains intact, in spite of total ablation of glucagon cells (Chapter 5) or elimination of the peripheral glucagon cells (Chapter 3) and other unintended adverse retina effects, compared to findings from previous studies involving QUIS (Chapter 2) of this thesis, is a novel finding. These results point to the same conclusion that glucagon cells themselves are not responsible for the decoding of the sign of optical defocus, but appear to have a role in fine-tuning of compensatory growth responses. The results of our experiments also suggest that the choroid may serve as an intermediate relay, and the altered anterior chamber development raise the further possibility that retina-derived growth modulatory factors also regulate the anterior segment, perhaps reaching this more remote site by diffusion forward through the vitreous chamber or via the uvea.
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Giovanzana, Stefano. "A virtual environment for modeling and analysis of human eye." Doctoral thesis, Università degli studi di Padova, 2011. http://hdl.handle.net/11577/3427528.
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The aim of this work is to develop a virtual environment for modelling and analyse individual virtual eyes which are able to integrate the modern imaging techniques input data. This environment is realized in 3D CAD software by means of specific plug-ins. The tools for analysing the virtual eye are based on ray-tracing and curvature analysis, while the shape of the eye is represented by NURBS or mesh surfaces. This thesis develops, and validates the use of, the plug-ins for the modelization of virtual eyes inside a 3D CAD environment; in particular a novel lens model whose shape is linked to geometrical and optical constraints was created. Shape was also tested on real crystalline images obtained with shadow photogrammetry. Moreover real eye topography was used for modelization of anterior cornea and preliminary results from ray tracing are shown. This model and the ray-tracing tools may be used in future works for design of ophthalmic, contact or intraocular lenses, specifically customised of a single ametropy.Lo scopo di questo lavoro è stato quello di sviluappare un ambiente virtuale per la modellazione e l’analisi di un occhio virtuale personalizzato, che fosse in grado di integrare le moderne tecniche di analisi ottica come dati di ingresso. Questo ambiente è stato sviluppato all’interno di un software CAD tramite l’ultilizzo di plug-in specifici. Gli strumenti utilizzati per analizzare l’occhio virtuale sono basati sul ray-tracing e sull’analisi di curvatura, mentre la geometria dell’occhio è stata modellizzata tramite l’utilizzo di superfici NURBS o mesh. La presente tesi sviluppa, e valida l’utilizzo, di codesti plug-in per la modellizzazione di un occhio virtuale in un ambiente CAD 3D; in particolare è stato creato un modello innovativo di lente, la cui forma è legata a vincoli geometrici ed ottici. La forma di tale lente è stata confrontata con cristallini reali le cui immagini sono state ottenute tramite fotografia ad ombra. Inoltre la topografia di un occho reale è state utilizzata per modellare la superficie anteriore della cornea e sono quindi riportati i risultati preliminari del ray-tracing. Questo modello e gli strumenti di ray-tracing utilizzati potranno essere utilizzati in futuro per la progettazione di lenti oftalmiche, a contatto o intraoculari specificatamente costumizzate sulle esigenze dell’ametrope.
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Hoseini, Yazdi Seyed Hosein. "Spatial characteristics of the response of the human choroid to imposed defocus." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/120362/1/Seyed%20Hosein_Hoseini%20Yazdi_Thesis.pdf.
Full textAbstract:
This thesis examined the thickness of the human choroid across a substantially larger region (~55°) than previously examined (~17°), its regional variation associated with myopia, and its short-term response to different spatial patterns of optical defocus. This research provided the first evidence of a local response of the choroid to a region specific pattern of myopic defocus in the human eye. These findings add to the current understanding of the choroid's contribution to vision dependent mechanisms of human eye growth and may assist in optimising the optical design of myopia control interventions.
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Rasengane, Tuwani A. "The incidence and distribution of ametropia in blacks in Umlazi." Thesis, 1988. http://hdl.handle.net/10413/9851.
Full textAbstract:
Age, sex, race, heredity, environment and nutrition have been
found to influence ametropia. In this study, the distribution of
refractive errors has been investigated in relation to age, sex,
race, education and near work, and lighting conditions. Visual
awareness and vision screening in pre-school and schoolchildren
were also investigated.
Data were collected using the Nikon auto-refractor, retinoscope,
Snellen V.A chart, and subjective techniques. 777 people were
refracted, whose ages ranged between four and eighty years.
Measurements were made in different sections of Umlazi township,
therefore people of different socio-economic sectors were
refracted.
Four year-old children were found to be hyperopic. Hyperopia
decreased and refraction shifted towards emmetropia. Myopia
started to appear at the age of ten. Myopia increased until the
age of twenty, and thereafter decreased slowly until the age of
thirty three, where the average refraction was emmetropia. From
age forty onwards, hyperopia was predominant.
The incidence of high astigmatism, high hyperopia and high myopia
is low in this community. Most people fall in the spherical
refractive error region of between -1.000 and +1.000. The curve
is leptokurtotic with highest peak around +0.250. The cylindrical
error is between -0.500 and -1.000.
No significant difference between sexes was found except at the
fourth age group (40-51), where females are more hyperopic than males. The other sex difference is at ages ten to twelve, where females develop myopia earlier than males. Illumination plays no important role in the development of refractive errors in this community. Education and near work seem to account very little to the development of myopia.
The influence of heredity on the development of ametropia was not
investigated in depth. However, there is no evidence of heredity
influencing the development of ametropia. There is a lack of vision screening and visual awareness.Thesis (M.Optom.)-University of Durban-Westville, 1988.
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Du, Toit Renee. "Visual and non-visual variables implicated in monovision wear." Thesis, 2014. http://hdl.handle.net/10210/11140.
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Xiang, Fan. "Preventing the epidemic of myopia in China : an integrated epidemiological and biological approach." Phd thesis, 2011. http://hdl.handle.net/1885/149803.
Full textAbstract:
Myopia is the most common refractive error. It is generally accepted that there is an epidemic of myopia in urban areas of East Asia, as more than 80% of the children who complete secondary school are shorted-sight, with around 20% highly myopic. Importantly, this problem is not unique to East Asia, and prevalence of myopia is increasing in other parts of the world. The high prevalence of myopia imposes costs for both optical correction and visual impairment. Furthermore, the high prevalence of severe myopia increases the risk of uncorrectable visual impairment and even blindness. Myopia has emerged as major heath issue in the world, and been included as one of the priority areas of Vision 2020.
The key findings of this thesis are: 1. The prevalence of myopia has increased progressively from 20-30% to over 80% over the past 100 years in East Asia, and it is plausible that a secular shift in life-style has taken place, resulting in more intensive education and less time spent outside by most children;
2. Environmental influences played an important role during the process, as in Guangzhou, most children now become myopic, and some become highly myopic, irrespective of the refractive status of their parents. There is an additional risk of myopia in children with myopic parents, and an increased risk of developing more severe myopia for those who had severe myopic parents. Exposure to the environment in younger generations did not simply shift the population mean of the refraction;
3. Increased rates of progression in a myopic direction and increased rates of axial elongation occur prior to the onset of clinical myopia. It might therefore be possible to initiate myopia prevention before the onset of myopia. Once a myopic refraction is established, the rates of axial elongation and myopic progression are reduced. The rapid slowing of axial elongation after the onset may suggest that myopic defocus is able to inhibit myopic progression to some extent.
4. The first two years of follow up of the Guangzhou Outdoor Activity Longitudinal Study showed promising results, with a consistent pattern of reduced axial elongation and myopia development in children with outdoor intervention, although greater exposure is needed to obtain clinically significant effects.
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Kruger, Elene. "Autokeratometric variation following large incision corneal wound closure by fibrin glue." Thesis, 2010. http://hdl.handle.net/10210/3117.
Full textAbstract:
M.Phil.Cataracts have been identified as one of the leading causes of blindness, especially in the developing world. The only presently known effective treatment for this growing problem is surgical removal of the opaque lens followed by replacement with an artificial intra ocular lens. Newer methods have brought greater success, and greater costs. For people in the developing world, these newer methods are not always an option. Together with the increased cost, there is a growing demand because of this worldwide problem. This increased need for surgery has lead to the development of waiting lists in the state funded hospitals. To qualify for a cataract extraction in most state funded hospitals, a best visual acuity of 6/60 is required, compared to the 6/12 to 6/24 levels required in the industrial countries and private practices. With these levels of visual impairment in the developing world, many patients are left functionally blind for long periods of time until cataract extraction can be performed. Older methods such as extra-capsular cataract extraction are still being used in the developing world. This is mostly due to the increased density of the cataracts at the time when the extraction can be performed because of the long waiting time leading to further maturation of the cataract. This method requires a large corneal incision, which is normally closed with nylon sutures. With this method of surgery meticulous wound closure is very important, and in many cases surgically induced astigmatism is one of the unwanted consequences. It was therefore decided, for the purpose of this study, to use autokeratometric data to explore the refractive effects of two different methods of corneal wound closure following planned extra-capsular cataract extraction (ECCE). Astigmatism is a major problem associated with extra capsular cataract extraction, especially when the wound is closed by means of sutures. Studies by Minassian et al. (2001), Jacobi (2003) and Dowler et al. (2000) all show that newer methods of cataract extraction making use of smaller incisions and therefore fewer sutures show faster recovery and less astigmatism. These methods are however mostly restricted to private practice, and therefore potentially unsuited for use in developing countries. The type of material used for wound closure is another very important factor. Depending on the method of suturing wound gape and wound compression can cause increased amounts of astigmatism. Using a method of wound closure that would cause less traction on the cornea could therefore cause less of a problem postoperatively. Tissue adhesives such as Tisseel® fibrin glue could be such an alternative. Studies by Henrick et al. (1987), Kim and Kharod (2007) and Bhatia (2006) show that fibrin glue forms a watertight, non irritating wound while promoting the healing process by the cross linking of collagen fibres.
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Khoza, Hllawulani Lizzy. "Risk Factors Associated with the Occurrence of Refractive errors among Secondary School Children in Malamulele Community, Limpopo Province." Diss., 2016. http://hdl.handle.net/11602/1040.
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Baloyi, Voster Hlawulani Austine. "The Pattern of Distribution of Refractive Error among Primary School Children of Malamulele Community, Vhembe District, Limpopo Province." Diss., 2016. http://hdl.handle.net/11602/850.
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HONG, CIH-LANG, and 洪次郎. "Measurement of Eye′s Refractive Error Based on Wavefront Sensing Principle." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/x9q9mn.
Full textAbstract:
碩士逢甲大學
視光科技碩士在職學位學程
107
The aim of this study is to evaluate eye’s refractive error by using an optical measurement system with wavefront analysis and wavefront sensing technology. In optical design theory, third-order aberrations and higher-order aberrations can cause image quality problems such as blur and distortion in human vision. Therefore, the optical measurement system with Shack-Hartmann wavefront sensor is used as a sensing element to perform wavefront respectively. The measurement of aberrations is carried out, and the Zernike polynomial is used to describe the quality of individual aberrations of the eyes. Various human wavefront aberration analysis is performed, and the factors and accuracy of refractive error are evaluated to solve the problem of abnormal visual quality. This study found that the Shack-Hartmann wavefront sensing technology serves as an optical measurement system that can quickly screen for three major eye diseases and objective visual quality analysis. Optical measurement system with wavefront analysis also allows the optometrist to understand the importance of each individual optical system, allowing for the assessment of eyeball aberrations and improving vision quality to aid vision correction.
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Hampson, Karen M., Matthew P. Cufflin, and Edward A. H. Mallen. "Sensitivity of Chaos Measures in Detecting Stress in the Focusing Control Mechanism of the Short-Sighted Eye." 2017. http://hdl.handle.net/10454/12300.
Full textAbstract:
yesWhen fixating on a stationary object, the power of the eye’s lens fluctuates. Studies have suggested that changes in these so-called microfluctuations in accommodation may be a factor in the onset and progression of short-sightedness. Like many physiological signals, the fluctuations in the power of the lens exhibit chaotic behaviour. A breakdown or reduction in chaos in physiological systems indicates stress to the system or pathology. The purpose of this study was to determine whether the chaos in fluctuations of the power of the lens changes with refractive error, i.e. how short-sighted a subject is, and/or accommodative demand, i.e. the effective distance of the object that is being viewed. Six emmetropes (EMMs, non-short-sighted), six early-onset myopes (EOMs, onset of short-sightedness before the age of 15), and six late-onset myopes (LOMs, onset of short-sightedness after the age of 15) took part in the study. Accommodative microfluctuations were measured at 22 Hz using an SRW-5000 autorefractor at accommodative demands of 1 D (dioptres), 2 D, and 3 D. Chaos theory analysis was used to determine the embedding lag, embedding dimension, limit of predictability, and Lyapunov exponent. Topological transitivity was also tested for. For comparison, the power spectrum and standard deviation were calculated for each time record. The EMMs had a statistically significant higher Lyapunov exponent than the LOMs ( 0.64±0.330.64±0.33 vs. 0.39±0.20 D/s0.39±0.20 D/s ) and a lower embedding dimension than the LOMs ( 3.28±0.463.28±0.46 vs. 3.67±0.493.67±0.49 ). There was insufficient evidence (non-significant p value) of a difference between EOMs and EMMs or EOMs and LOMs. The majority of time records were topologically transitive. There was insufficient evidence of accommodative demand having an effect. Power spectrum analysis and assessment of the standard deviation of the fluctuations failed to discern differences based on refractive error. Chaos differences in accommodation microfluctuations indicate that the control system for LOMs is under stress in comparison to EMMs. Chaos theory analysis is a more sensitive marker of changes in accommodation microfluctuations than traditional analysis methods.
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Barrett, Brendan T., Jonathan C. Flavell, S. J. Bennett, Alice G. Cruickshank, Aleksandra M. Mankowska, J. M. Harris, and John G. Buckley. "Vision and visual history in elite/near-elite level cricketers and rugby-league players." 2017. http://hdl.handle.net/10454/13587.
Full textAbstract:
YesBackground: The importance of optimal and/or superior vision for participation in high-level sport remains the subject of considerable clinical research interest. Here we examine the vision and visual history of elite/near-elite cricketers and rugby-league players. Methods: Stereoacuity (TNO), colour vision, and distance (with/without pinhole) and near visual acuity (VA) were measured in two cricket squads (elite/international-level, female, n=16; near-elite, male, n=23) and one professional rugby-league squad (male, n=20). Refractive error was determined, and details of any correction worn and visual history were recorded. Results: Overall, 63% had their last eye-examination within 2 years. However, some had not had an eye examination for 5 years, or had never had one (near-elite-cricketers: 30%; rugby-league players: 15%; elite-cricketers: 6%). Comparing our results for all participants to published data for young, optimally-corrected, non-sporting adults, distance VA was ~1 line of letters worse than expected. Adopting α=0.01, the deficit in distance-VA deficit was significant, but only for elite-cricketers (p<0.001) (near-elite cricketers, p=0.02; rugby-league players, p=0.03). Near-VA did not differ between subgroups or relative to published norms for young adults (p>0.02 for all comparisons). On average, stereoacuity was better than in young adults, but only in elite-cricketers (p<0.001; p=0.03, near-elite-cricketers; p=0.47, rugby-league -players). On-field visual issues were present in 27% of participants, and mostly (in 75% of cases) comprised uncorrected ametropia. Some cricketers (near-elite: 17.4%; elite: 38%) wore refractive correction during play but no rugby-league player did. Some individuals with prescribed correction choose not to wear it when playing. Conclusion: Aside from near stereoacuity in elite-cricketers, these basic visual abilities were not better than equivalent, published data for optimally-corrected adults. 20-25% exhibited sub-optimal vision, suggesting that the clearest possible vision might not be critical for participation at the highest levels in the sports of cricket or rugby-league. Although vision could be improved in a sizeable proportion of our sample, the impact of correcting these, mostly subtle, refractive anomalies on playing performance is unknown.
Funded by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC) grants BB/J018163/1, BB/J016365/1 and BB/J018872/1.
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Chen, Jing-Jie, and 陳敬杰. "The relationship between the shapes of highly myopic eyes and their peripheral refraction errors by using high-resolution three-dimensional magnetic resonance imaging." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/50538490612604109043.
Full textAbstract:
碩士中山醫學大學
生物醫學科學學系碩士班
104
Purpose: This study aims to determine whether the relative peripheral refractive errors and the shape of retina by high-resolution three-dimensional magnetic resonance imaging in high myopia. Methods: Sixteen young adults with high myopia (over＞6.00 D) and nineteen emmetropic ( +0.50 to -0.50 D) young adults were investigated. An open-field auto-refractor was used to measure on- and off-axis refractions in horizontal meridian every 3° out to 30° in nasal and temporal retina, and in vertical meridian every 3° out to 12° in superior and inferior retinal. Axial ocular dimensions were measured by A-scan ultrasonography. Axial (horizontal through middle of eye), sagittal (vertical through axis) and tangential (horizontal through axis) sections were taken with a magnetic resonance imaging. Result: High myopic subjects had greater relative hyperopia in the periphery 30° temporal (+2.48 ± 0.90 D),30° nasal (+2.68 ± 1.16 D), 9° Superior (+0.64 ± 0.58 D) and 12° Inferior (+0.65 ± 0.63 D), indicating a prolate ocular shape (longer axial length than equatorial diameter), compared with relative peripheral myopia and an oblate shape (broader equatorial diameter than axial length) for emmetropes 30° temporal (-1.64 ± 0.42 D)and 30° nasal(-1.39 ± 0.44 D), 9° Superior (- 0.55 ± 0.27D) and 12° Inferior (-0.860 ± 0.29 D) .High myopic eyes showed much larger in all three dimensions, but more so in length (26.15 ± 1.05 mm) than in height (24.59 ± 0.87 mm) and more so in height than in width (24.41 ± 1.21mm). Emmetropic eyes showed the similar in three dimensions (height is 23.58 ± 0.61 mm, length is 23.40 ± 0.68 mm, and width is 23.19 ± 0.90 mm). In high myopic groups, the curvature of retina showed a significant negative correlation with the relative peripheral refraction(Temporal：Pearson r = -0.459；P＞0.01；Nasal：Pearson r = -0.277；P = 0.011；Superior：Pearson r = -0.066；P = 0.679；Inferior：Pearson r = -0.260；P = 0.096). Conclusions: In this study, the emmetropic groups showed relative peripheral myopic refrction and oblate ocular shape；The high myopic groups showed relative peripheral hyperopic refraction and prolate ocular shape. In high myopic eyes are negative correlation with the curvature of retina and relative peripheral refraction.