Eye movements, search and perception of visual field defects in glaucoma
Glaucoma is a progressive disease of the optic nerve that can result in irreversible loss of visual function and impairment in everyday visual tasks. The experimental studies described in this thesis primarily aim to investigate the performance of people with glaucoma on search and other visual tasks whilst simultaneously monitoring eye movements, making comparison with age-related visually healthy people. In an experiment focussing on visual search, a patient group (n=30) took significantly longer on average to find a target in images of everyday scenes than controls (n=30). Furthermore, comparison of eye movements made by the participants during this task revealed there was a statistically significant reduction (6%) in saccade rate in the patients compared to the controls, and that saccade rate correlated with performance. Similar differences in eye movements were observed when the same groups passively viewed a selection of images in a slideshow. A bivariate contour ellipse (BCE) analysis revealed that, on average, patients viewed smaller regions of the images compared to the controls. Eye movement differences between patients and controls were also examined in a different cohort of people with glaucoma (n=14) and visually healthy controls (n=22) whilst they watched a selection of Hazard Perception Test driving films. Saccade rate of the patients was found to increase by 9%, though results from the BCE analysis suggested the average size of viewing area was similar in both groups. Finally, a novel interview-based study of 50 people with glaucoma provides evidence that patients do not perceive their visual field defect as a black ‘tunnel’ effect, or as ‘black patches’, but more like blurred regions: this finding may, for example, impact on how glaucomatous visual field loss is depicted in patient information about the condition. In conclusion, the results from this thesis show how visual loss from glaucoma influences how patients perceive and react to their visual environment. The principal findings from the studies described in this thesis also show, for the first time, that eye movement analysis could provide a window into the functional deficits associated with glaucoma.
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