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While prolonged nearwork is considered to be an environmental risk factor associated with myopia development, an underlying genetic susceptibility to nearwork-induced accommodative adaptation may be one possible mechanism for human myopia development. As the control of accommodation by the autonomic system may be one such genetically predetermined system, this research sought to investigate whether an anomaly of the autonomic control of accommodation may be responsible for myopia development and progression. The emphasis of this work was determining the effect of altering the sympathetic input to the ciliary muscle on accommodation responses such as tonic accommodation and nearwork-induced accommodative adaptation in myopes and non-myopes. The first study of the thesis was based on observations of Gilmartin and Winfield (1995) which suggested that a deficit in the sympathetic inputs to the ciliary muscle may be associated with a propensity for myopia development. The effect of ß-antagonism with timolol application on accommodation characteristics was studied in different refractive error groups. Our results support the previous findings that a deficit of sympathetic facility during nearwork was not a feature of late-onset myopia. However it was found that classifying myopes according to stability of their myopia and their ethnic background was important and this allowed differentiation between accommodation responses and characteristics of the ciliary muscle autonomic inputs, with the greatest difference observed between Caucasian stable myopes and Asian progressing myopes. Progressing myopes, particularly those with an Asian background, demonstrated enhanced susceptibility to nearwork-induced accommodative adaptation and this was suggested to result from a possible parasympathetic dominance and a relative sympathetic deficit to the ciliary muscle. In contrast, stable myopes, particularly those with an Asian background, demonstrated minimal accommodation changes following nearwork (counter-adaptation in some cases), and increased accommodative adaptation with ß-antagonism, suggesting sympathetic dominance as the possible autonomic accommodation control profile. As ethnic background was found to be an important factor, a similar study was also conducted in a group of Hong Kong Chinese children to investigate if enhanced susceptibility to nearwork-induced changes in accommodation may explain in part the high prevalence of myopia in Hong Kong. Despite some minor differences in methodology between the two studies, the Hong Kong stable myopic children demonstrated counter-adaptive changes and greater accommodative adaptation with timolol, findings that were consistent with those of the adult Asian stable myopes. Both Asian progressing myopic children and adults also showed greater accommodative adaptation than the stable myopes and similar response profiles following ß-adrenergic antagonism. Thus a combination of genetically predetermined accommodation profiles that confer high susceptibility and extreme environmental pressures is a likely explanation for the increase in myopia over the past decades in Asian countries. The hypothesis that a sympathetic deficit is linked to myopia was also investigated by comparing the effect of â-stimulation with salbutamol, a ß-agonist, on accommodation with that of ß-antagonism using timolol. It was hypothesized that salbutamol would have the opposite effect of timolol, and that it would have a greater effect on subjects who demonstrated greater accommodative adaptation effects, i.e. the progressing myopes, compared to those who showed minimal changes in accommodation following nearwork. Consistent with the hypothesis, the effect of sympathetic stimulation with salbutamol application was only evident in the progressing myopes whom we hypothesized may have a parasympathetic dominance and a relative sympathetic deficit type of autonomic imbalance while it did not further enhance the rapid accommodative regression profile demonstrated by the stable myopes. Characteristics of the convergence system and the interaction between accommodation and convergence were also investigated in the Hong Kong children. No significant differences in response AC/A ratios between the emmetropic, stable and progressing myopic children were found and it was concluded that elevated AC/A ratios were not associated with higher myopic progression rate in this sample of Hong Kong children. However, ß-adrenergic antagonism with timolol application produced a greater effect on accommodative convergence (AC) in stable myopic children who presumably have a more adequate, robust sympathetic input to the ciliary muscle, but had little effect on AC of progressing myopic children. This finding again points to the possibility that the autonomic control of the accommodation and convergence systems may be different between stable and progressing myopia. The primary contribution of this study to the understanding of myopia development is that differences in the autonomic control of the ciliary muscle may be responsible for producing anomalous accommodation responses. This could have significant impact on retinal image quality and thus results in myopia development. This knowledge may be incorporated into computer models of accommodation and myopia development and provides scope for further investigation of the therapeutic benefits of autonomic agents for myopia control.

No / This review aims to disentangle cause and effect in the relationship between anisometropia and amblyopia. Specifically, we examine the literature for evidence to support different possible developmental sequences that could ultimately lead to the presentation of both conditions. The prevalence of anisometropia is around 20% for an inter-ocular difference of 0.5D or greater in spherical equivalent refraction, falling to 2-3%, for an inter-ocular difference of 3D or above. Anisometropia prevalence is relatively high in the weeks following birth, in the teenage years coinciding with the onset of myopia and, most notably, in older adults starting after the onset of presbyopia. It has about one-third the prevalence of bilateral refractive errors of the same magnitude. Importantly, the prevalence of anisometropia is higher in highly ametropic groups, suggesting that emmetropization failures underlying ametropia and anisometropia may be similar. Amblyopia is present in 1-3% of humans and around one-half to two-thirds of amblyopes have anisometropia either alone or in combination with strabismus. The frequent co-existence of amblyopia and anisometropia at a child's first clinical examination promotes the belief that the anisometropia has caused the amblyopia, as has been demonstrated in animal models of the condition. In reviewing the human and monkey literature however it is clear that there are additional paths beyond this classic hypothesis to the co-occurrence of anisometropia and amblyopia. For example, after the emergence of amblyopia secondary to either deprivation or strabismus, anisometropia often follows. In cases of anisometropia with no apparent deprivation or strabismus, questions remain about the failure of the emmetropization mechanism that routinely eliminates infantile anisometropia. Also, the chronology of amblyopia development is poorly documented in cases of 'pure' anisometropic amblyopia. Although indirect, the therapeutic impact of refractive correction on anisometropic amblyopia provides strong support for the hypothesis that the anisometropia caused the amblyopia. Direct evidence for the aetiology of anisometropic amblyopia will require longitudinal tracking of at-risk infants, which poses numerous methodological and ethical challenges. However, if we are to prevent this condition, we must understand the factors that cause it to develop.

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The aim of this study was to determine the prevalence and causes as well as the risk factors of visual impairment (VI) and blindness among Black South Africans with diabetes mellitus (DM) aged 40 years and older in Mopani District, Limpopo province, South Africa. This was a cross-sectional study in which Black South Africans with DM aged ≥40 years old were examined for VI and blindness. In addition, anthropometric as well as risk factors for VI and blindness were studied. A total of 225 participants were selected from seven Public Health Facilities in Mopani District. Data was collected using standard optometric instruments, anthropometric instruments and structured interviews. Data analysis was done using the Statistical Analysis System (SAS) and Microsoft Excel software packages. The ages of the participants ranged from 40 to 90 years with a mean of 61.5±10.49 years. There were more females (71.5%) than males (28.4%). The prevalence of uncorrected VI and blindness in the right eyes of the participants was 70.7% and 3.6%, respectively. In the left eyes, it was 72% and 3.1%, respectively. However, following optical correction, the prevalence in right eyes was 41.3% and 3.6%, respectively. In the left eyes, it was 42.2% and 3.1%, respectively. Risk factors that were individually associated with VI and blindness include age, educational qualification, monthly income, knowledge of DM types, oral DM treatment (pills), losing weight, compliance to losing weight, family history of DM, physical activity, and date of last eye examination .When logistic regression was used, knowledge of DM types, pills, and compliance to losing weight, family history of DM, monthly income and physical activity remained associated with VI and blindness. The high prevalence of VI in this diabetes population was not primarily due to DM itself, but due to refractive error and cataract, conditions which have effective and easy treatments. A total of 84% of the participants were visually impaired due to either refractive error or cataract or both and only 3.8% due to diabetes retinopathy. It is therefore recommended that appropriate and affordable refraction and cataract surgical services be made available and accessible to this population / Health Studies / D. Litt. et Phil. (Health Studies)

Beaucoup d'adolescents sous-estiment leur inconfort visuel, bien qu'il puisse affecter leur scolarité. La prévalence des troubles visuels chez des participants âgés de quinze à vingt-deux ans a été étudiée et les résultats obtenus ont été comparés à leur niveau scolaireEntre septembre 2012 et avril 2013, quatre cents jeunes gens âgés de quinze à vingt-deux ans ont répondu à un questionnaire relatif à des signes d’asthénopie, suivi d’un examen visuel (réfraction, fonctionnement accommodatif et vision binoculaire), afin de détecter des gênes visuelles dont ils pourraient ne pas être spontanément conscients. Lorsque des problèmes visuels ont été détectés, il a été proposé aux participants de passer un examen ophtalmologique et un bilan orthoptique. Puis, le niveau scolaire de ces quatre cents jeunes a été expertisé. Les participants ont ensuite été revus pour déterminer si le port d'une correction optique adaptée et/ou la prise en charge orthoptique ont permis d'obtenir une amélioration de la performance scolaire.Les résultats indiquent que le score au questionnaire est significatif pour prédire la probabilité d’avoir une faible performance scolaire et d’avoir des troubles visuels, que les anomalies de la réfraction et de l’accommodation ont un réel impact sur la performance scolaire et plus encore, que ce sont les troubles de la vision binoculaire qui sont les plus pénalisants. Surtout, l’absence d’une plainte visuelle spontanément exprimée ne permet pas de conclure à l’absence de problèmes visuels.Une fois la performance scolaire contrôlée par des variables utilisées habituellement pour l’expliquer (e.g. retard scolaire, CSP du chef de famille, sexe, etc.), une partie non négligeable des difficultés scolaires des participants proviennent de problèmes liés à la vision. Par conséquent, un dépistage systématique des troubles visuels chez les adolescents semble nécessaire, d’autant plus s’ils rencontrent des difficultés scolaires. Par ailleurs, le questionnaire mis en place dans l’anamnèse semble être un outil efficace dans la détection de la présence de troubles et mériterait d’être validé sur un plus large échantillon. / Many students understate their visual discomfort, although it may have an educational impact. We studied the prevalence of visual disorders among students and compared these results to their academic level.Between September 2012 and April 2013, four hundred students between fifteen and twenty two years of age responded to a questionnaire followed by a visual screening (refraction and binocular vision) in order to detect any visual discomfort that they might be unaware of. When visual problems were detected, the participants were asked to have an ophthalmology and orthoptic assessment. Then the participants’ academic performance was appraised and subjects were reviewed to determine whether wearing the appropriate optical correction or taking orthoptic care have improved their grades.The results indicate that the questionnaire score is very significant to predict the probability of having academic difficulties or vision problems, that ametropia and accommodation anomalies increase academic difficulties and that binocular vision disorders are even more disadvantageous. Moreover, not spontaneously expressing visual discomfort doesn’t mean that there are no visual defects.Once controlled by variables commonly used to explain academic difficulties (e.g. academic delay, occupational category, gender, etc.) a significant proportion of participants’ academic difficulties are related to vision anomalies. Therefore, vision screening among adolescents appears to be necessary, especially if there are academic difficulties. In addition, the questionnaire used in case history seems to be an effective tool to detect vision anomalies and should be validated with a larger sample.

The aim of this study was to determine the prevalence and causes as well as the risk factors of visual impairment (VI) and blindness among Black South Africans with diabetes mellitus (DM) aged 40 years and older in Mopani District, Limpopo province, South Africa. This was a cross-sectional study in which Black South Africans with DM aged ≥40 years old were examined for VI and blindness. In addition, anthropometric as well as risk factors for VI and blindness were studied. A total of 225 participants were selected from seven Public Health Facilities in Mopani District. Data was collected using standard optometric instruments, anthropometric instruments and structured interviews. Data analysis was done using the Statistical Analysis System (SAS) and Microsoft Excel software packages. The ages of the participants ranged from 40 to 90 years with a mean of 61.5±10.49 years. There were more females (71.5%) than males (28.4%). The prevalence of uncorrected VI and blindness in the right eyes of the participants was 70.7% and 3.6%, respectively. In the left eyes, it was 72% and 3.1%, respectively. However, following optical correction, the prevalence in right eyes was 41.3% and 3.6%, respectively. In the left eyes, it was 42.2% and 3.1%, respectively. Risk factors that were individually associated with VI and blindness include age, educational qualification, monthly income, knowledge of DM types, oral DM treatment (pills), losing weight, compliance to losing weight, family history of DM, physical activity, and date of last eye examination .When logistic regression was used, knowledge of DM types, pills, and compliance to losing weight, family history of DM, monthly income and physical activity remained associated with VI and blindness. The high prevalence of VI in this diabetes population was not primarily due to DM itself, but due to refractive error and cataract, conditions which have effective and easy treatments. A total of 84% of the participants were visually impaired due to either refractive error or cataract or both and only 3.8% due to diabetes retinopathy. It is therefore recommended that appropriate and affordable refraction and cataract surgical services be made available and accessible to this population / Health Studies / D. Litt. et Phil. (Health Studies)

MPH / Department of Public Health / See the attached abstract below