published_or_final_version / abstract / Social Work and Social Administration / Doctoral / Doctor of Philosophy

This research investigated the influence of the normal aging process on truly photopic achromatic and chromatic retinal increment threshold over an extensive range of colored targets. It was found that for both achromatic and chromatic retinal thresholds there is a significant correlation between advancing age and the stimulus luminance intensity at threshold across the visible spectrum. This correlation is greater for the short wavelength range than for both the middle and the long wavelength ranges (r² (achromatic)= 0.43; r²(chromatic) = 0.49. In addition, a small exploratory study was completed which examined the role of prereceptoral changes in these age-related differences in color vision function. Results from this preliminary study (Experiment II) support the supposition that prereceptoral factors cannot account for all of the age-related losses that are seen in visual function, particularly in the middle and long wavelength ranges of the visible spectrum. / Arts, Faculty of / Psychology, Department of / Graduate

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This research focuses on the grief and emotional reactions, especially frustration, of adventitiously visually impaired adults following loss of sight. The traditional grief-following loss theory with the assumption of a time-limited linear grief process, accompanied by diminishing emotions and culminating with acceptance and adjustment has been challenged. Chronic grief assumes a recurrent and continuous grief process, accompanied by increased emotions associated with continual losses related to a chronic loss, such as visual impairment. The question of whether there is a relation between length of time of adventitious visual impairment and the healing affect of time on grief and frustrations has been examined by quantitative and qualitative investigations. The answer to the question of whether time changes and heals everything is not necessarily the case. As always there are more questions than answers, and this research provides further insight into the real world of adventitious visual impairment. / Psychology / M.A. (Psychology)

~ ..•.. There are two types of Oxford Filter; blue filters enhance short wavelength light and yel,low enhance long wavelength light. These filters have previously been shown to improve reading performance, vergence eye movements and perception of visual form and motion. In this thesis the effects of such filters were examined in both an unselected primary school population, and in a clinical population of children with identified visual and/or reading difficulties. A school based visual screening study established that just over 40% of children identified a filter as beneficial when viewing text. These children reported a significantly higher number of visual symptoms and had significantly reduced convergence and accommodation eye movements compared to non-filter choosers. A further trial of filter use revealed that those using blue filters made significant improvements in accommodative function and in spelling ability. A cross-over, randomised controlled trial was conducted in the clinical sample with psychometric, orthoptic and psychophysical assessments administered before and after filter use. Poor readers made significant improvements in reading following filter use, but a smaller dyslexic group were not found to improve their reading. Performance on a Matrices task significantly improved after using yellow filters specifically. There was also evidence that children with reduced saccades improved their spelling with the use of yellow filters, but had reduced spelling following blue use. Although filters impacted upon both orthoptic and literacy measures these improvements appear not to be causally linked. A random dot kinematogram task (RDK) revealed a correlation between magnocellular functioning under blue and yellow lighting conditions and reading; lower reading was associated with poorer RDK thresholds. This association was specific to reading and not evident in relation to dyslexia. Visual search accuracy was also shown to improve significantly after the use of blue and yellow filters. Together these findings have implications for the treatment of orthoptic abnormalities and literacy performance.

A Distrofia Muscular de Duchenne (DMD) é uma doença recessiva ligada ao cromossomo X, causada por deleção ou mutação na proteína distrofina, e afeta 1 para cada 3.500 nascidos vivos do sexo masculino. O gene da distrofina é o maior gene do genoma humano e, além das proteínas de tamanho total, ao menos outras 5 isoformas foram identificadas até o momento. A isoforma total da distrofina e outras menores como a Dp260 (transcrita pelo promotor localizado no exon 30; encontrada na camada plexiforme externa da retina) e Dp71 (transcrita pelo promotor localizado no exon 63; encontrada nas células de Muller e membrana limitante interna da retina) são expressas na retina, dentre vários tecidos do corpo. Alterações nos eletrorretinogramas (ERG) de sujeitos com DMD já foram descritas na literatura. Redução da amplitude da onda-b e ERG negativo (razão das.amplitudes entre as ondas b e a menor que 1) são os achados mais comuns principalmente em sujeitos com deleção posterior ao exon 30. Embora estas alterações sejam conhecidas, poucos estudos avaliaram funcionalmente a visão destes sujeitos e, estes concluíram que os sujeitos com DMD apresentam visão de cores, acuidade visual e motilidade ocular normais. Como estas conclusões não refletem os achados eletrofisiológicos, o presente trabalho teve por objetivo aprofundar a avaliação de funções visuais em sujeitos com DMD, utilizando testes psicofisicos mais precisos e sensíveis que os métodos anteriormente empregados. Aplicamos uma bateria de testes que avaliou: a visão de cores (Cambridge Colour Test, Anomaloscópio de Neitz tipo I, lshihara e AO H-R-R) e a sensibilidade ao contraste de luminância (espacial e temporal), em 54 meninos (idade média =14,2 ± 4,1) com DMD, bem como o ERG em um subgrupo de 11 sujeitos. De acordo com a região da deleção no gene foram constituídos 3 grupos: grupo 1 (n=20) - sem deleção, grupo 2 (n=7) - com deleção anterior ao exon 30, grupo 3 (n=27) com deleção posterior ao exon 30. O grupo controle foi composto por 35 meninos com idade equiparada (médias = 15,4 ± 3,9). Os resultados mostraram que 52% dos sujeitos do grupo 3 apresentam defeitos de visão de cores. Surpreendentemente, a maioria destes sujeitos apresentou um defeito no eixo protan-deutan. Os três grupos apresentaram redução na sensibilidade ao contraste espacial e ao contraste temporal para todas as freqüências espaciais e temporais testadas. Houve uma tendência do grupo 3 de ter os piores resultados de contraste espacial. Para os resultados de contraste temporal, diferiram estatisticamente do grupo controle apenas os sujeitos do grupo 3 que tinham defeito de visão de cores. Os parâmetros do ERG de campo total replicaram os dados da literatura mostrando uma diminuição da amplitude e um aumento da latência da onda-b, além de uma razão b/a menor que l. A análise individual dos potenciais oscilatórios mostrou redução significante no 3° e no 4° potenciais, indicando que tanto a via dos cones quanto a dos bastonetes estão afetadas nos sujeitos com.DMD e deleção posterior ao exon 30. A constatação das maiores alterações de função visual nos sujeitos com deleção posterior ao exon 30 leva a sugerir que a distrofina Dp260 tem papel importante na fisiologia retiniana. Em conclusão, o presente trabalho demonstrou que a DMD é acompanhada por perdas visuais em várias funções e que estas perdas podem ser causadas principalmente por modificações na isoforma Dp260 da distrofina / Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder, caused by deletion or mutation in the protein dystrophyn, which affects 1:3500 live male births. The dystrophyn gene is the largest gene in the human genome. The full-length dystrophyn and at least other 5 isoforms have been identified. They are expressed in several tissues of the body including the retina, where the shorter isoforms Dp260 (transcribed by a promoter at the exon 30; founded in the outer plexiform layer of the retina) and Dp71 (transcribed by a promoter at the exon 63; founded in the Muller cells and inner limiting membrane of the retina) have been shown. Alterations in the electroretinograms (ERG) of these subjects have been described in the literature. 13-wave amplitude reduction and -a negative ERG (b/a wave amplitude ratio < 1) are the most common alterations found in subjects with gene deletion downstream exon 30, transcribes Dp260 isoform. Although these alterations are known, the only study that performed 1 evaluations of visual functions in these subjects concluded that they showed normal color vision, visual acuity and ocular motility results. Since these conclusions do not reflect the electrophysiological findings the objective of the present study was to further evaluate the visual function of DMD subjects using more sensitive and precise psychophysical tests than the methods used before. A battery of visual tests was used to evaluate color vision (Cambridge Colour Test, Neitz-1 Anomaloscope, Ishihara and AO H-R-R), luminance contrast sensitivity (spatial and temporal) in 54 boys (mean age = 14,2 ± 4,1) with DMD, and the ERG was also measured in a subgroup (n = 11) of these boys. According with the region of gene deletion, the subjects were divided in 3 groups: group 1 (n = 20) - without gene deletion, group 2 (n = 7) - with gene deletion upstream exon 30, group 3 (n = 27) - with gene deletion downstream exon 30. The control group was composed of 35 age-matched boys (mean-- 15,4 ± 3,9). Our results showed that 52% of the group 3 subjects had color vision defects. Surprisingly, almost all of these boys had a defect in the proten-deutan axis. In all three groups, spatial and temporal contrast sensitivities were lower than those of controls, for all spatial and temporal frequencies tested. Group 3 subjects had a tendency not statistically significant to present the worst results of spatial contrast sensitivities. Temporal contrast sensitivities were significantly different from controls' only for group 3 subjects with color vision defects. The full-field ERG results showed a b-wave amplitude reduction, a longer implicit time and a b/a ratio less than 1. Oscillatory potentials were significantly lower in the 3° and 4° potentials suggesting that that both cone and rod pathways were affected in the DMD subjects with deletion downstream exon 30. To our knowledge there are no descriptions of visual function defects in DMD subjects. The finding that the largest alterationslosses of visual function oceur in the subjects with deletion downstream exon 30 leads us to suggest that the dystrophyn Dp260 has an important role in the physiology of the retina physiology. In conclusion, the present study showed that DMD is accompanied losses in several visual functions and that these losses may be caused mainly by impairment in the Dp260 dystrophyn isoform

Thesis (MPH.) -- University of Limpopo, 2015 / Purpose: The purpose of this study was to determine the prevalence and causes of visual impairment (low vision and blindness) among eye clinic patients at Nkhensani hospital in Limpopo province, South Africa. Methods: This was a cross sectional design in which 400 stratified participants aged ≥ 6 years were selected {100 participants in each stratum (6 – 18; 19 – 35; 36 – 59 and ≥ 60 years)}. Presenting, pinhole and best corrected visual acuities were measured using a logMAR E chart. Where reduced visual acuity (VA) was due to uncorrected refractive errors (UREs), ophthalmic lenses were used to compensate for the refractive errors using subjective refraction method and best corrected VA was measured. All participants underwent external and internal ocular examinations using ophthalmoscope to detect eye diseases. Participants with ocular pathology were referred to the ophthalmic nurse and/or ophthalmologist for further management. Refractive error findings were elaborated on in this study in order to highlight the importance and impact of this eye condition. Results: The ages of participants ranged from 6 to 92 years with mean of 39.5 ± 23.5 years. They included 161 (40.3%) males and 239 (59.8%) females. The prevalence of significant visual impairment (SVI) (VA < 6/18 to no light perception, i.e. low vision and blindness), low vision and blindness based on presenting visual acuity (PVA) in the right eye were 34.8%, 16.3% and 18.5% respectively while the prevalence based on the best corrected VA were 24.0%, 7.5% and 16.5% respectively. Based on the PVA, there was a significant association between age (Chi = 71.6; df =3; p = 0.00) and gender (Chi = 8.9; df =1; p = 0.003) with visual impairment (VI) of the right eye. In the left eye, the prevalence of SVI, low vision and blindness based on PVA were 35.8%, 17.5% and 18.3% respectively, while the prevalence based on best corrected VA were 24.8%, 8.5% and 16.3% respectively. Based on PVA, there was a significant association between age and visual impairment in the left eye (Chi = 52.9; df =3; p = 0.00) but there was no association between gender and VI (Chi = 1.9; df =1; p = 0.163). In both eyes, the prevalence of SVI, low vision and blindness based on PVA were 27.0%, 17.5% and 10.3% respectively, while the prevalence based on best corrected VA were 16.8%, 3.8% and 9.5% respectively. Based on the PVA, there was a significant association between age and VI (Chi = 54.1; df =3; p = 0.00) and gender and VI (Chi = 4.7; df =1; p = 0.03) in both eyes. iv The causes of significant visual impairment were uncorrected refractive errors (38.0%), cataract (25.9%) and glaucoma (17.6%) in both eyes. Among all participants, the leading causes of low vision based on presenting VA were uncorrected refractive errors (56.7%), cataract (20.9%) and glaucoma (9.0%). The main causes of blindness in both eyes were cataract (34.1%), glaucoma (31.7%) and corneal anomalies (17.1%) based on presenting visual acuity. After optical corrections, the main causes of VI were cataract (39.4%), glaucoma (28.8%) and corneal anomalies (18.2%). The main causes of low vision were cataract (42.9%), glaucoma (21.4%) and corneal anomalies (17.9%), while the main causes of blindness were cataract (39.5%), glaucoma (34.2%) and corneal anomalies (15.8%). Conclusion: The findings in this study indicate that the overall prevalence of visual impairment, low vision and blindness among patients attending the Nkhensani hospital eye clinic were 27.0%, 16.8% and 10.3% respectively. The main causes of visual impairment, low vision and blindness were uncorrected refractive errors, cataract and glaucoma. A focus on the optical correction of refractive errors and surgical intervention in the case of cataract would lead to a significant reduction in the burden of visual impairment among patients who utilise Nkhensani hospital for eye care services. Also, early detection and appropriate management of glaucoma will reduce the burden of this ocular morbidity. A significant proportion of these prevailing ocular morbidities are avoidable and with appropriate management, visual impairment is preventable.

Theories on the impact of visual loss tend to generalise and can simplify complex issues. Two extreme views are challenged that portray the impact of visual loss as catastrophic or as a minor inconvenience. The argument is put forward that the impact of visual loss can lessen with improved interaction, and this theory is tested by the author questioning and modifying her own interaction. The following themes are explored: limbo status and self-acceptance; the common stresses experienced when asking for help; and discriminatory attitudes. The research is action based, and the emphasis is on how individuals adjust and adapt to loss, rather than the stresses experienced. / Master of Science (Hons)

Myocilin, expressed in the trabecular meshwork of the eye, has been linked to inherited primary open-angle glaucoma (POAG). The biological function of myocilin is unknown, but mutant myocilin exhibits a gain-of-function mechanism, aggregating within the endoplasmic reticulum of human trabecular meshwork cells, causing cell stress and eventually apoptosis. After apoptosis occurs, the trabecular meshwork is compromised, leading to an increase in intraocular pressure, a symptom of glaucoma. In this thesis, I have expressed and purified the wild-type olfactomedin (OLF) domain and 24 reported disease-causing variants. I developed a facile thermal stability assay using differential scanning fluorimetry, which follows the unfolding of a protein through the fluorescence of a dye sensitive to hydrophobic regions of a protein. Also in this thesis I have determined melting temperatures for the wild-type and for each of the disease-causing mutants. I have tested the stability of the mutants in the presence of seven osmolytes, with sarcosine and trimethylamine-N-oxide restoring the melting temperature closest to wild-type. Additionally, I expressed and purified three reported single nucleotide polymorphisms (SNPs) (E352Q, E396D, K398R), which are considered benign variants. Variants were also compared by circular dichroism, revealing high b-sheet content and wild-type structure. When compared to previous studies, there is a positive correlation between the melting temperature, and previously reported qualitative assays, which measure the mutant myocilin solubility in detergent, secretion from mammalian cells, and aggregation propensity. Taken together, these data give insight into the relationship between glaucoma genotypes and phenotypes.

This study explored the experience of disability as recounted by school aged, visually impaired adolescents. The primary aim was to explore the manner in which these adolescents thought about, understood and coped with their disability. A second aim explored the extent to which participants’ experiences mirrored those reported in the literature. The design of the study was qualitative with an orientation toward social constructionism. Nine partially sighted and seven blind adolescents comprised the two cohorts of participants who participated in the study. One of the most notable findings supported the argument that disability is a socially constructed phenomenon. Some insights, drawn from psychoanalysis, were also found to be useful. Other findings, a critique of the study, and suggestions for future research are also provided. One of the most important of these involves evaluating the negative and positive consequences of inclusive education.