The relationship between retinal structure and function has received a sizeable amount of attention in vision-related research over the past 2-3 decades, particularly in the field of glaucoma where it is estimated that 60.5 million people worldwide will experience the disease by the year 2010. Many studies have directed attention towards the development of novel techniques to detect and evaluate glaucomatous loss much earlier than conventional means, with mixed levels of success. Still uncertain however, is how our visual perception changes in early glaucoma and how this relates to the way neural units are lost from the visual system. In this thesis, we revisited the classical theory of spatial summation, which describes the ability of the visual system to integrate light energy over space and we investigate how this is affected in early glaucoma. In particular, we investigated changes in the area of complete spatial summation (Ricco's area) in the ageing eye and in glaucoma and assessed how this parameter affects the results that we find using conventional perimetric tests. Furthermore, we investigated the relationship between changes in spatial summation and the changing architecture of the retina as determined using both functional (peripheral grating resolution acuity) and imaging techniques (retinal nerve fibre layer thickness - OCT). We have found that Ricco's area is significantly enlarged in early glaucoma for achromatic stimuli and for chromatic stimuli under selective S-cone conditions and that this enlargement in the area over which visual signals are pooled can account for most of the sensitivity loss that is reported using standard contrast sensitivity tests with a fixed stimulus size. We have also found a significant, yet weak relationship between Ricco's area and peripheral grating resolution acuity as well as retinal nerve fibre layer thickness. Here we consider the effect of stimulus size on perimetric thresholds and offer a method of stimulus modulation that might afford a greater glaucoma signal than conventional methods.

The general aim of the thesis was to deduce whether selected naturally occurring flavonoids (genistein, epicatechin gallate (EC), epigallocatechin gallate (EGCG), baicalin) attenuate various secondary insults that may cause death of ganglion cells in primary open angle glaucoma (POAG). An ischemic insult to the rat retina significantly causes the inner retina to degenerate indexed by changes of various antigens, proteins and mRNAs located to amacrine and ganglion cells. These changes are blunted in animals treated with genistein as has been shown for ECGC. Studies conducted on cells (RGC-5 cells) in culture showed that hydrogen peroxide, L-buthionine sulfoximine (BSO)/glutamate and serum deprivation (mimicking oxidative stress), rotenone, sodium azide (affecting mitochondria function in specific ways) and light (where the mitochondria are generally affected) all generated reactive oxygen species and caused death of RGC-5 cells. EGCG was able to attenuate cell death caused by hydrogen peroxide, sodium azide and rotenone. Only EC was able to attenuate BSO/glutamate-induced cell death, in addition to cell death caused by hydrogen peroxide and rotenone. Genistein had no positive effect on cell death in experiments carried out on RGC-5 cells. Exposure of RGC-5 cells to flavonoids showed that EC and EGCG increased the mRNA expression of endogenous antioxidants such as HO-l (heme oxygenase 1) and Nrf-2 (nuclear erythroid factor-z-related factor 2). Light insult, rotenone and sodium azide activate the p38 (protein kinase 38) pathway, while only light and rotenone activate the JNK (c-Jun amino-terminal kinase) pathway. Serum deprivation affects mitochondrial apoptotic proteins causing an increase in the ratio of Bax/Bcl2 (Bax: Bcl-2-associated X protein; Bcl-2: B-cell lymphoma 2). An insult of light to RGC-5 cells, unlike that induced by sodium azide, is inhibited by necrostatin-I and causes an activation of AlF (apoptosis-inducing factor) with alpha-fodrin being unaffected. These studies suggest that ganglion cell death caused by insults as may occur in POAG involves various cellular signaling pathways. The selected flavonoids have diverse actions in increasing cellular defense mechanisms, and in negating the effects of ischemia and specific types of oxidative stress. The results argue for the possible use of flavonoids in the treatment of POAG to slow down ganglion cell death.