Keratan sulfate (KS) is an elongated glycosaminoglycan (GAG) chain found throughout the cornea, the clear tissue at the front of the eye. It is thought that KS plays a specialized role in maintaining the ordered spatial arrangement of collagen fibrils that comprise the thickest layer of the cornea, the stroma. Repeating N-­‐acetylglucosamine (GlcNAc) and galactose monosaccharides make up the fine structure of KS, and sulfate groups frequently modify their C-­‐6 positions. Recent studies have linked improper sulfation of GlcNAc residues to macular corneal dystrophy, a vision condition characterized by a progressive loss of corneal transparency. Since then, in vitro experiments have implicated four enzymes in highly sulfated KS biosynthesis. It is currently believed that β-­‐1,3-­‐N-­‐ acetylglucosaminyltransferase 7 (β3GnT7), corneal GlcNAc 6-­‐O sulfotransferase (CGn6ST), and β-­‐1,4-­‐ lactosyltransferase 4 (β4GalT4) sequentially catalyze the addition of GlcNAc, transfer sulfate to its C-­‐6 position, and link galactose to the growing KS backbone, respectively. The fourth enzyme, KS galactose 6-­‐O sulfotransferase (KSGal6ST) is thought to act last, sulfating galactose residues. Mutant mice deficient in CGn6ST, KSGal6ST, or β3GnT7 were recently developed to investigate the consequences of dysfunctional sulfo-­‐ or glycosyltransferases on corneal morphology. Electron microscopy and immunohistochemistry data in this thesis showed that the systemic absence of CGn6ST or β3GnT7 resulted in a corneal stroma devoid of KS, but mutation of only KSGal6ST led to a KS phenotype similar to that of wild type controls. Western blot analysis conducted on β3GnT7-­‐null corneas indicated that KS assumed an unusually truncated form, as compared to wild type controls. A secondary result evident in electron micrographs was that in cases where KS levels dropped below the detectable threshold (i.e. in CGn6ST and β3GnT7 mutant corneas), a concurrent appearance of atypically elongated GAGs was visible, suggesting a compensatory mechanism to preserve corneal organization. Since the unusual GAGs were susceptible to chondroitinase ABC digestion, it is thought they are comprised of chondroitin/dermatan sulfate (CS/DS). Studies using high performance liquid chromatography were also undertaken to establish protocols in which future work could quantify the change in CS/DS expression observed in CGn6ST and β3GnT7 mutant corneas.

It has been demonstrated repeatedly, over a period of many years that some animals can perceive magnetic field parameters and use this sensory information to their advantage. The sensory mechanisms involved are, however, still poorly understood. Due to a general lack of understanding of magnetoreception and its properties, experiments to date have been somewhat disjointed with many, often very different, investigative approaches being employed. As a result, direct corroboration of results is uncommon and progress is often slow. Advancement of this field is important for numerous reasons, such as improving knowledge of factors affecting animal migration in a time of concern over climate change and the possible imminent change in earth’s magnetic field parameters. Perhaps most significantly, such studies might provide a potential keystone in the study of the function of quantum mechanical processes in biological systems. The current study utilises a novel approach, designed to ensure improved reproducibility. Reported here for the first time, prepulse inhibition of a startle response is used to investigate magnetoreception in the homing pigeon (Columba livia). This powerful, well-characterised paradigm relies on reflexive behaviours and therefore ensures an objective method for demonstrating the perception of a stimulus. Visual psychophysics and polarised light vision are also explored. Proof of concept is provided for the use of prepulse inhibition to investigate magnetoreception. The value of using liquid crystal displays in an investigation of pigeon head movements, in magnetoreception and more generally, is demonstrated. A new, low invasiveness technique for tracking head movements is described. The need to eliminate anthropogenic electromagnetic signals in order to carry out reliable magnetoreception experiments is highlighted. Suggestions are also made regarding possible future directions of research in this area.

Glaucoma is an optic neuropathy characterised by the loss of retinal ganglion cells (RGC). Dendritic atrophy occurs early in the disease, prior to soma and axonal degeneration. RGCs exhibit reduced branching density and dendritic field size. This thesis seeks to further characterise dendritic atrophy in glaucoma in the context of two external factors that may contribute to the disease pathology – immune system effects mediated via complement and the influence of the perineuronal net (PNN), a specialised extracellular matrix that surrounds RGCs. RGC morphology was investigated in a rat bead model of experimental glaucoma using ballistic labelling techniques; morphological changes were related to synaptic loss and PNN composition using immunohistochemistry. A model was derived for the classification of diseased RGCs in order to prevent labelling bias in subsequent investigations. The immune system was modulated using a complement inhibitor (using a transgenic mouse and pharmacological agent in rats) and PNNs disrupted using the bacterial enzyme Chondroitinase ABC. Experimental glaucoma caused significant dendritic loss, with partial protection conferred by both complement inhibition and PNN digestion. Analysis of retinal sections also revealed partial protection of synapses. PNNs did not show any changes in their composition in the rat in experimental glaucoma but human glaucoma eyes showed increased glycosaminoglycan sulphation in the RGC layer which was correlated with visual deficit. Manipulation of the RGC external environment therefore proved successful in protecting from dendritic atrophy.

The purpose of this thesis was to assess long-term outcomes of the visual dysfunction arising from the ocular toxicity associated with the anti-epileptic drug vigabatrin (VGB). The risk of vigabatrin-associated visual field loss (VAVFL) with increasing exposure to VGB was modelled from retrospectively collected data from a cohort of 147 individuals (median exposure 7.9 years; IQR 3.6, 11.0). The modelled frequency of VAVFL increased with increasing exposure and plateaued at 75-80% after approximately 6 years duration and 5kg cumulative dose. The relationship between the numbers of retinal ganglion cell soma and axons, derived by standard automated perimetry and time-domain optical coherence tomography (TDOCT), respectively, was evaluated in 24 individuals with VAVFL and in 16 exposed to vigabatrin but with normal fields (VGBN). A strong linear association was present between the two outcomes, which was suggestive of an optic neuropathy, and was similar to the association for a control group of 18 individuals with open angle glaucoma. A follow-up visual field, after a median interval of 7.0 years (IQR 6.5, 7.6) was determined in 19 individuals with VAVFL and in 8 with VGBN, after a median withdrawal from VGB of 7.1 years (IQR 5.4, 8.4). No consistent trend was noted for either a deterioration or improvement in the field. A follow-up scan of the peripapillary retinal nerve fibre layer (RNFL) thickness, by TDOCT, after a median interval of 6.5 years (IQR 5.8, 6.9) was obtained in 13 individuals with VAVFL and in 4 with VGBN, after a median withdrawal from VGB of 8.0 years (IQR 5.3, 10.2). No consistent trend was noted for either a deterioration or improvement of the RNFL thickness. The macular thickness was evaluated by TDOCT in 32 individuals with VAVFL and in 14 with VGBN. No difference in thickness was noted between the two groups.

: Infantile nystagmus (IN) is a pathological condition of continuous, horizontal eye oscillations. Despite ongoing eye movements, those with IN do not experience oscillopsia, i.e. the illusory perception that the environment is moving to-and fro. The correct use of neural compensation for their eye movements, just as in typical individuals, is hypothesised to account for this lack of oscillopsia. This neural mechanism requires that an estimate of eye velocity (‘extra-retinal signal’) be compared to an estimate of the motion of the retinal image (‘retinal signal’), and any difference due to object motion. Despite this hypothesis, there have been no previous investigations on how accurately those with IN can estimate object motion. Even in typical adults, eye movement compensation is not perfect, which underlies a number of pursuit-based illusions. One such illusion, the Filehne illusion can be used to investigate the relative mismatch between the extra-retinal and retinal signals as individuals judge their perception of stationarity while attempting to follow a moving target. This illusion was used to investigate, through comparison with typical individuals, whether those with IN correctly recover object motion. Experiments were conducted to characterise the ability of those with IN to fixate as well as follow targets, using a novel two-dimensional eye movement measure. Under repeated testing, the fixation gaze angle at which the IN oscillation is minimum (a null zone) was not consistent. Moreover, those with IN were unable to accurately or precisely follow targets using their slow phase. Results from a comparison of fixation and pursuit performance in those with IN suggested no difference in either the accuracy or precision. Importantly, the psychophysical judgements of those with IN pursuit eye movements are prone to similar compensation errors as typical controls. However, the mechanisms by which this is achieved will require further exploration.

A sensory nerve supply is crucial for optimal function of the cornea. However, the mechanisms for successful innervation and the signalling pathways between nerves and their target tissue are not fully understood. Engineered tissue substitutes can provide controllable environments in which to study tissue innervation. I have therefore engineered human corneal substitutes that promote nerve in-growth in a pattern similar to in vivo re-innervation. The methodology developed for the fabrication of such an innervated model cornea and for subsequent investigation of the function of these nerves is discussed in this thesis. Briefly, nerve in-growth into the tissue-engineered cornea is enhanced by the addition of laminin and nerve growth factor, but not retinoic acid. I demonstrated that these nerves are morphologically equivalent to natural corneal nerves and make appropriate contact with their target cells, which consequently, were found to be required for their survival. The nerves had functional sodium channels and generated action potentials similar to those of native nerve endings. I also demonstrated that the nerves could respond appropriately to chemical and physical stimuli and play an important role in the overall functioning of the bioengineered tissue. The presence of nerves conferred some protection to the epithelium from chemical insult and differential retention of sodium was observed within the nerve fibres themselves. As such, this model could be further developed for use as an in vitro alternative to animals for safety and efficacy testing of chemicals and drugs. Based on the concepts developed for these in vitro innervated corneas, hybrid biosynthetic matrices with the proper dimensions, transparency and biomechanical properties for use as corneal replacements in transplantation were also developed. These matrices were successfully implanted into corneas of pigs. Regeneration of corneal tissue and nerves was observed, along with restoration of sensory function. The basic model developed therefore can be used for studying corneal wound healing, nerve-corneal cell interactions and provides a basis for developing corneal replacements for transplantation.

The purpose of this research was to develop a psycho-educational counselling programme for the handling of people suffering from a severe ophthalmologically challenge. It appears that people who are severely ophthalmologically challenged do not only experience it physically but also experience negative feelings such as a crumbling self-image, a lack of self-confidence, various fears as well as depression. Their state of mind induces a change with regard to their interpersonal relationships because they avoid social interaction, as well as feelings of loss and they experience a change regarding acceptance by others. However, it has transpired that people who are severely ophthalmologically challenged make use of various mechanisms such as support by others, the gathering of information and humour in order to handle their ophthalmological challenges. Society attaches so much importance to external appearance which does not make it easier for a person suffering from a physical "dissimilarity" and it influences the person's metal health. As a consequence the researcher began asking the following questions: 1. What does the world in which a severely ophthalmologically challenged person live, look like? 2. How can a psycho-educational counselling programme lead such a person to mental health and self-acceptance? A qualitative, explorative, descriptive and contextual research design was followed. The research took place in four phases: In phase 1 the experiences of people with severe ophthalmological challenges were explored and described, by means of phenomenological, unstructured, in-depth interviews with the patient and significant others such as parents, spouses and children. In phase 2 the psycho-educational programme for the person with severe ophthalmological challenges was developed based on the results of phase 1. In phase 3 this psycho-educational counselling programme was implemented. During phase 4 the evaluation of the psycho-educational programme took place by means of a single case study. The motivation behind the development of such a programme was to create a framework in which people with severe ophthalmological challenges could develop constructive interpersonal communication skills. They could also be afforded the opportunity to reflect through discourse. By attaching significance to their discourse they can accept their changing circumstances and act self-assertively. The programme has been facilitated so that psycho-educationists and other professionals may use it to facilitate the counselling programme to improve mental health for people who are severely ophthalmologically challenged. / Prof. C.P.H. Myburgh Prof. M.Poggenpoel

M.Phil. / Vision is the most dominant of the five senses and plays an important role in our daily lives. The sensory information obtained through vision is of utmost importance in the way we perceive and respond to the world around us. Vision has often been neglected when evaluating the performance of athletes. Would you be able to catch a ball with your eyes closed, more than likely not? This example indicates the necessity of vision to perform specific motor tasks, such as is required in sports. Anatomically there are differences between the male and female body and therefore a variance in performance should be expected. The fact that visual skills can be leamed or even taught brings about the question of what effect age, gender and experience have on the performance of an athlete on these specific visual skills. The purpose of this study was to evaluate the variations between male and female visual skills measured during a sports vision evaluation. A protocol was devised to create a set of norms for the athletes tested and these norms were then compared to previous norms set out for elite athletes. In this study 209 female and 251 male non-elite athletes were tested. The subjects varied between the age of 18 and 19 and were in their first year of study at the then Rand Afrikaans University, now known as the University of Johannesburg. The study indicated that a significant difference in performance between the gender groups does exist and that separate norms should indeed be used when evaluating male and female athletes. The female athletes performed better on the Visual Acuity and Colour vision tests, with the male athletes performing better on the Contrast Sensitivity Row E, Fusion Flexibility, Eye-Hand Coordination Pro and Re Action, Eye-Body Coordination, Visual Reaction Time Right and Left hand, Visual Adjustability Left and Right Base positions and Visualization tests. Equal performance was achieved in the Contrast Sensitivity Row A; B, C and D, Stereopsis and Visual Adjustability Up and Down Base position tests. It is thus clear that the males performed better on most of the tests done.

BACKGROUND: Complaints of vitreous floaters are not new to veteran ophthalmologists, and many can attest to the reported burden symptomatic floaters have on visual clarity and quality of life. Classic treatment paradigms recommend indefinite observation or, in the case of severely bothersome floaters, pars plana vitrectomy (PPV). Despite the proven efficacy, PPV requires intraocular access and has a side effect profile that warrants severe visual impairment to justify the risks of surgery. Floater laser treatment has the potential to fill the treatment gap as a less invasive alternative using photodisruption to vaporize floaters. Studies have attempted to quantify the efficacy of Nd:YAG laser treatment with moderate success, but the safety profile of the laser floater treatment (LFT) is still limited in duration of follow-up. OBJECTIVE: To analyze the efficacy and safety of Nd:YAG laser vitreolysis performed in-clinic as measured by number of sessions, patients who went on to pursue secondary vitrectomy, and a self-reported survey comparing visual satisfaction before and after LFT. METHODS: In a retrospective study, 32 eyes with a history of symptomatic floaters of varied etiology were treated with the Ellex Nd:YAG laser set to single-shot mode with a maximal pulse energy of 7mJ. The number of treatments each patient underwent until receiving full visual benefit served as an objective measure of the efficacy of the laser. Secondary vitrectomy patients who failed laser vitreolysis were sampled as evidence of inadequate response to treatment. A self-administered survey explored patient satisfaction in terms of overall quality of vision, frequency/severity of floaters, and impact floaters have on activities of daily life (ADLs) before and after the laser, graded on a 4-point scale. RESULTS: Laser Floater Treatment performed in-clinic at Boston Vision/Boston Laser (BVBL) yielded moderate success in resolving symptomatic floaters, as indicated by improved mean patient scores following treatment for quality of vision (+1.13), frequency/severity of floaters (+1.00), and impact floaters have on ADLs (+1.33) when compared to pretreatment scales. The mean number of discrete treatment sessions to gleam full benefit of laser vitreolysis was 2.5 sessions per patient. Approximately 6% (2/32) patients failed vitreolysis and went on to pursue PPV. CONCLUSIONS: Our results showed an improvement of mean patient scores in overall quality of vision, severity of floaters, and floaters’ impact by at least 1 scale point, supporting the efficacy of laser vitreolysis. Patients underwent a mean of 2.5 treatment sessions, and offering multiple sessions likely bolstered the overall efficacy of the procedure. The sample population of 32 yielded only two patients (6%) who went on to pursue secondary vitrectomy, suggesting LFT could potentially serve as another treatment option filling the gap between observation and PPV.

Ma thèse est constituée de trois études cliniques différentes ayant comme sujet les enfants porteurs d’une trisomie 21. L’objectif principal est d’analyser leur particularités oculaires et d’essayer de les corréler avec d’autres aspects cliniques et physiologiques spécifiques au syndrome, notamment avec le processus d’angiogenèse. La première étude clinique utilise l’imagerie de l’iris en lumière standard et infrarouge, et démontre que les taches de Brushfield et leur équivalent dans la population générale, les nodules de Wölfflin, décrits dans leur large majorité dans des yeux de couleur claire se retrouvent aussi présents dans les yeux foncés. Ces taches iriennes, ainsi que l’amincissement irien périphérique et la rareté des sillons de contraction iriens, peuvent représenter des signes d’angiogenèse diminuée in utero. La deuxième étude clinique analyse le segment postérieur de l’œil chez les enfants porteurs d’une trisomie 21 versus contrôles. Le nerf optique semble être plus souvent anormal chez les enfants porteurs d’une trisomie 21. De même, on observe plus fréquemment des zones d’atrophie péripapillaire et un aspect tigroïde au fond de l’œil chez les enfants porteurs d’une trisomie 21 versus contrôles. Le troisième étude clinique a comme objectif d’évaluer les vaisseaux qui croissent le bord du nerf optique chez les enfants porteurs d’une trisomie 21 et de les comparer avec ceux des membres de sa famille et de cas contrôles appariés pour le sexe et l’âge. Nous avons en plus analysé quelques importants facteurs d’angiogenèse (endostatine, VEGF A et angiopoiétine 1) et nous avons essayé d’établir une corrélation entre leur niveaux sériques et le nombre des vaisseaux qui croissent le bord du nerf optique. Ce nombre de vaisseaux, ainsi que les facteurs d’angiogenèse étudiés, sont significativement différent entre patients porteurs d’une trisomie 21 et contrôles. Par analogie avec d’autres maladies lors desquelles l’angiogenèse est perturbée, comme par exemple le syndrome papillorénal où les anomalies rénales sont fréquentes, nous nous attendions que les reins des enfants porteurs d’une trisomie 21 soient également touchés par différentes anomalies .Pour prouver cela, nous avons analysé la morphologie et la fonction rénale des enfants trisomiques versus un groupe contrôle apparié pour le sexe et l’âge. Pour la première fois, in vivo, avec l’aide de l’échographie rénale, nous montrons que les reins sont plus petits chez les enfants porteurs d’une trisomie 21 comparé avec ceux des enfants à développement normal. Nous confirmons également les résultats d’autres études qui décrivent plus fréquemment d’autres anomalies rénales chez les enfants porteurs d’une trisomie 21.Grâce à ces trois études, cette thèse apporte une série d’observations nouvelles concernant les particularités oculaires, générales et concernant l’angiogenèse chez les enfants porteurs d’une trisomie 21 et contribue ainsi à l’avancement des connaissances liées à cette condition. / This thesis is composed of three different clinical studies. The main objective of this thesis is to link the ocular particularities of children with Down syndrome with other clinical and physiological aspects specific to the condition, especially with their angiogenesis status.The first clinical study used iris imaging in standard and infrared light to demonstrate that Brushfield spots and their equivalent in the general population, Wölfflin nodules, which were previously mainly described in light colored eyes, are also found in dark eyes. These iris nodules, as well as iris peripheral thinning and the rarity of the iris contraction furrows, may represent signs of decreased angiogenesis in utero.The second clinical study analyzes the posterior segment of the eye in children with Down's syndrome versus controls. The optic nerve appear to be more often abnormal in children with Down's syndrome. Similarly, areas of peripapillary atrophy and peripapillary tessellation are more frequently observed in children with Down syndrome when compared to controls.The third clinical study aims to assess the retinal vessels crossing the disc margin in children with Down syndrome and controls. We also analyzed some important factors of angiogenesis (endostatin, VEGF A and angiopoietin 1) and we tried to establish a correlation between their serum levels and the number of vessels that cross the edge of the optic nerve. The number of vessels, as well as the angiogenesis factors studied, are significantly different between patients with Down syndrome and controls. By analogy with other diseases in which angiogenesis is dysregulated, such as papillorenal syndrome, kidney abnormalities are too be expected also in children with Down syndrome. Thus, we analyzed the renal morphology and function of children with Down syndrome and compare it with an age- and sex- matched control group. For the first time, with the help of renal ultrasound, we show that the kidneys are smaller in children with trisomy 21. This thesis generates a series of novel observations concerning the ocular, general and angiogenesis particularities in children with Down syndrome, contributing to the advancement of knowledge related to this condition and to a patient care. / Doctorat en Sciences médicales (Médecine) / info:eu-repo/semantics/nonPublished