Spatial summation and the structure/function relationship with age and in glaucoma

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.EThOS - Electronic Theses Online ServiceGBUnited Kingdo