Thesis (MPH.) --University of Limpopo, 2015 / Background: Uncorrected refractive errors remain a public health problem among different population and age groups worldwide, including South Africa. Refractive error has serious visual and functional impacts on those affected. In children, refractive errors may negatively affect the academic pursuits and activities of daily living such as reading. Aims and Objectives: To determine and document the prevalence, types and magnitude together with age and gender differences of refractive errors among primary school children in Motherwell Township, Eastern Cape Province, South Africa. Methods: This was a quantitative, cross sectional refractive error study. Four hundred and twenty one (421) school children aged 7 – 14 years were randomly selected from five randomly selected schools in Motherwell Township, Eastern Cape Province, South Africa. Visual examination which included unaided and aided visual acuity (with LogMAR E chart), non-cycloplegic autorefraction, subjective refraction, internal and external examination of the eye using an ophthalmoscope was conducted. Refractive errors were measured with an autorefractor, refined subjectively and findings presented in spherical form. Hyperopia was defined as a spherical equivalent (SE) of +0.50 D or greater, myopia as spherical equivalent of -0.50 D or greater. A cylindrical power of -0.50 DC (D cylinder) or greater was considered as astigmatism. Results: The prevalence of hyperopia, myopia and astigmatism among the children were 25.2%, 18.7% and 58.0% respectively. Hyperopia ranged from +0.50 to +3.62 D and myopia ranged from -0.50 D to -20.25 D in the right eyes with a mean of -0.17 ± 1.7 D. In the left eye, hyperopia ranged from +0.50 to +2.62 D and myopia ranged from -0.50 to -20.62 D with a mean of -0.12 ± 1.7 D. Astigmatism in the right eyes ranged from -0.50 to -5.50 D with a mean of -0.6 ± 0.52 D and in the left eye ranged from -0.50 to -4.00 D with a mean of -0.6 ± 0.45 D respectively. Association between hyperopia and age was not statistically significant (p = 0.839), also refractive error and gender was statistically insignificant (p = 0.120). Against-the-rule (ATRA) astigmatism (43.4%) was more common, followed by with-the-rule (WTRA) astigmatism (39.0%) and oblique, (all other meridians) (17.6%). There was a significant association between types of astigmatism and age (p = 0.05), more so inter-gender difference in the prevalence of different types of astigmatism was not statistically significant (p = 0.774). Conclusion: The study concludes that refractive error has high prevalence of 43.9% in this children population. Astigmatism (58.0%) was more common followed by hyperopia (25.2%) v and myopia (18.7%). Although hyperopia was not age dependent, there was obvious relationship pattern between female genders and hyperopia in the present study. Population-based vision screening or at least school visual screening in the rural communities of Motherwell Township is, therefore recommended. Vision screening and proper eye examination with appropriate optical compensation will improve the activity of daily living and quality of life of those affected. Key words: Refractive error, hyperopia, myopia, astigmatism, school children

Background: The prevalence of uncorrected refractive error among school-age children is on the rise with a detrimental effect on academic performance and socio-economic status of those affected. School vision screening appears to be an effective way of identifying children with uncorrected refractive error so early intervention can be made. Despite the increasing popularity of school vision screening programs in recent times, there is a lot of debate on its effectiveness in reducing the proportion of children with uncorrected refractive error in the long term especially in settings where resources are limited. Objective: To assess the effectiveness of school vision screening programs in reducing children with uncorrected refractive error in LMIC. Search Methods: To identify studies suitable for this systematic review, a comprehensive and systematic search strategy was employed. We searched various databases and the search was restricted to articles published in English. We included RCTs, cross-sectional studies, case-control studies, and cohort studies. Participants included school children who had undergone vision screening as part of school vision screening programs in the LMIC setting and found to have a refractive error. Two independent reviewers screened the result of the search output and performed a full-text review of the search result to identify papers that met the pre-defined inclusion criteria. Data extraction and risk of bias assessment for the included studies was performed by the two independent reviewers and discrepancies were resolved by consensus and through consultation. The certainty of the evidence was assessed using the GRADE approach. Main Result: We found thirty relevant studies conducted in ten different countries that answered our review questions. Our review showed that school vision screening may be effective in reducing the proportion of children with an uncorrected refractive error by 81% (95% CI: 77%; 84%, moderate certainty evidence), 24% (95% CI: 13%; 35%, moderate certainty evidence,) and 20% (95% CI: 18%; 22%, moderate certainty evidence) at two, six, and more than six months respectively after its introduction. Our review also suggest that school vision screening may be effective in achieving 54% (95% CI: 25%; 100%, moderate certainty evidence), 57% (95% CI:46%; 70%, low certainty evidence), 38% (95% CI: 29%; 51%, moderate certainty evidence) and 41% (95% CI: 24%; 68%, low certainty evidence) level of spectacle wear compliance among school children at less than three months, at three months, at six months and at more than six months respectively after its introduction. Our review further found moderate to high certainty evidence indicating that school vision screening together with the provision of spectacles may be relatively cost-effective, safe and has a positive impact on the academic performance of children. Conclusion: Result of this review shows that school vision screening together with the provision of spectacle may be a safe and cost-effective way of reducing the proportion of children with uncorrected refractive error with a long-term positive impact on academic performance of children. Most of the studies included in this review were however conducted in Asia and the applicability of this finding to countries in other regions especially those outside the LMIC circle is not clear.

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yes / When 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.

Yes / PURPOSE. To test the hypothesis that emmetropization buffers against genetic and environmental risk factors for myopia by investigating whether risk factor effect sizes vary depending on children’s position in the refractive error distribution. METHODS. Refractive error was assessed in participants from two birth cohorts: Avon Longitudinal Study of Parents and Children (ALSPAC) (noncycloplegic autorefraction) and Generation R (cycloplegic autorefraction). A genetic risk score for myopia was calculated from genotypes at 146 loci. Time spent reading, time outdoors, and parental myopia were ascertained from parent-completed questionnaires. Risk factors were coded as binary variables (0 = low, 1 = high risk). Associations between refractive error and each risk factor were estimated using either ordinary least squares (OLS) regression or quantile regression. RESULTS. Quantile regression: effects associated with all risk factors (genetic risk, parental myopia, high time spent reading, low time outdoors) were larger for children in the extremes of the refractive error distribution than for emmetropes and low ametropes in the center of the distribution. For example, the effect associated with having a myopic parent for children in quantile 0.05 vs. 0.50 was as follows: ALSPAC: age 15, –1.19 D (95% CI –1.75 to –0.63) vs. –0.13 D (–0.19 to –0.06), P = 0.001; Generation R: age 9, –1.31 D (–1.80 to –0.82) vs. –0.19 D (–0.26 to –0.11), P < 0.001. Effect sizes for OLS regression were intermediate to those for quantiles 0.05 and 0.50. CONCLUSIONS. Risk factors for myopia were associated with much larger effects in children in the extremes of the refractive error distribution, providing indirect evidence that emmetropization buffers against both genetic and environmental risk factors. / UK Medical Research Council and Wellcome (grant ref: 102215/2/13/2), and the University of Bristol provided core support for ALSPAC. This research was specifically funded by the UK National Eye Research Centre (grant SAC015), the Global Education Program of the Russian Federation government, a PhD studentship grant from the UK College of Optometrists (“Genetic Prediction of Individuals At-Risk for Myopia Development”), and an NIHR Senior Research Fellowship award SRF-2015-08-005. The Generation R study is supported by the Erasmus Medical Center, Rotterdam, Erasmus University, Rotterdam, the Netherlands; the Netherlands Organization of Scientific Research (NWO); Netherlands Organization for the Health Research and Development (ZonMw); the Ministry of Education, Culture and Science; the Ministry for Health,Welfare and Sports; the European Commission (DG XII); European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (grant 648268); the Netherlands Organization for Scientific Research (NWO, grant 91815655); and Oogfonds, ODAS, Uitzicht 2017-28 (LSBS, MaculaFonds, Oogfonds).

Yes / Cross-sectional and longitudinal studies have consistently reported an association between education and myopia. However, conventional observational studies are at risk of bias due to confounding by factors such as socioeconomic position and parental educational attainment. The current study aimed to estimate the causal effect of education on refractive error using regression discontinuity analysis. Methods: Regression discontinuity analysis was applied to assess the influence on refractive error of the raising of the school leaving age (ROSLA) from 15 to 16 years introduced in England and Wales in 1972. For comparison, a conventional ordinary least squares (OLS) analysis was performed. The analysis sample comprised 21,548 UK Biobank participants born in a nine-year interval centered on September 1957, the date of birth of those first affected by ROSLA. Results: In OLS analysis, the ROSLA 1972 reform was associated with a −0.29 D (95% confidence interval [CI]: −0.36 to −0.21, P < 0.001) more negative refractive error. In other words, the refractive error of the study sample became more negative by −0.29 D during the transition from a minimum school leaving age of 15 to 16 years of age. Regression discontinuity analysis estimated the causal effect of the ROSLA 1972 reform on refractive error as −0.77 D (95% CI: −1.53 to −0.02, P = 0.04). Conclusions: Additional compulsory schooling due to the ROSLA 1972 reform was associated with a more negative refractive error, providing additional support for a causal relationship between education and myopia. / Global Education program of the Russian Federation government (DP) and an NIHR Senior Research Fellowship award SRF-2015-08-005 (CW), The Department for Health through an award made by the NIHR to the Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust, and UCL Institute of Ophthalmology, London, United Kingdom (grant no. BRC2_009). Additional support was provided by The Special Trustees of Moorfields Eye Hospital, London, United Kingdom (grant no. ST 12 09)

Yes / Background: Myopia has been shown to have a complex mode of inheritance, being influenced by both genetic and environmental factors. Here, an introduction into myopia genetics is given, with the shortcomings of current genetic prediction for myopia discussed, including the proportionally limited research on genetic prediction in people of non-European ancestry. A previously developed genetic risk score derived from European participants was evaluated in participants of non-European ancestry. Methods: Participants from UK Biobank who self-reported their ethnicity as “Asian”, “Chinese”, or “Black” and who had refractive error and genetic data available were included in the analysis. Ancestral homogeneity was confirmed using principal component analysis, resulting in samples of 3500 Asian, 444 Chinese, and 3132 Black participants. A published refractive error GWAS meta-analysis of 711,984 participants of European ancestry was used to create a weighted genetic risk score model which was then applied to participants from each ethnic group. Accuracy of genetic prediction of refractive error was estimated as the proportion of variance explained (PVE). Receiver operating characteristic (ROC) curves were developed to estimate myopia prediction performance at three thresholds: any myopia (equal to or more than 0.75D), moderate myopia (between -3.00D and -4.99D) and high myopia (equal to or more than -5.00D). Odds ratios for myopia were calculated for the participants in the top 10th or 5th percentile of genetic risk score distribution, comparing them to the remainder of the population. Results: The PVE value for refractive error was 6.4%, 6.2%, and 1.5% for those with Asian, Chinese and Black ethnicity, respectively (compared to 11.2% in Europeans). Odds ratios for any myopia and moderate myopia development for those within the top 10th and 5th percentile of genetic risk were significant in all ethnic groups P<0.05). However, the genetic risk score was not able to reliably identify those at risk of high myopia, other than for participants of Chinese ethnicity (P<0.05). Conclusion: Prediction of refractive error in Asian, Chinese and Black participants was ~57%, 55% and 13% as accurate in comparison to prediction in European participants. Further research in diverse ethnic populations is needed to improve prediction accuracy. / This research has been conducted using the UK Biobank Resource (applications #17351). UK Biobank was established by the Wellcome Trust; the UK Medical Research Council; the Department for Health (London, UK); Scottish Government (Edinburgh, UK); and the Northwest Regional Development Agency (Warrington, UK). It also received funding from the Welsh Assembly Government (Cardiff, UK); the British Heart Foundation; and Diabetes UK. Collection of eye and vision data was supported by The Department for Health through an award made by the NIHR to the Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust, and UCL Institute of Ophthalmology, London, United Kingdom (grant no. BRC2_009). Additional support was provided by The Special Trustees of Moorfields Eye Hospital, London, United Kingdom (grant no. ST 12 09). Many parts of this project were performed during the time that author Neema Ghorbani Mojarrad was supported by the College of Optometrists with a Postgraduate Scholarship.

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Clinical wavefront-guided corneal ablation has been now the most technologically advanced method to reduce the dependence of glasses and contact lenses. It has the potential not only to eliminate spherocylindrical errors but also to reduce higher-order aberrations (HOA). Recent statistics show that more than 96% of the patients who received laser in situ keratomileusis (LASIK) treatment reported their satisfaction about the improvement on vision, six months after the surgery. However, there are still patients complaining that their vision performance did not achieve the expectation or was even worse than before surgery. The reasons causing the unexpected post-surgical outcome include undercorrection, overcorrection, induced HOA, and other postoperative diseases, most of which are caused by inaccurate ablation besides other pathological factors. Therefore, to find out the method to optimize the LASIK procedures and provide a higher surgical precision has become increasingly important. A proper method to calculate ablation profile and an effective way to control the laser beam size and shape are key aspects in this research to resolve the problem. Here in this Master of Philosophy degree thesis, the author has performed a meticulous study on the existing methods of ablation profile calculation and investigated the efficiency of wavefront only ablation by a computer simulation applying real patient data. Finally, the concept of a refractive surgery system with dynamical beam shaping function is sketched, which can theoretically overcome the disadvantages of traditional procedures with a finite laser beam size.