Differential aspects of spatial vision in subjects presenting with either macular degeneration or visual snow

• Main Author: Alissa, R.
• Published: City, University of London 2018
• Subjects: RE Ophthalmology
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.753693

The aim of this study was to investigate differential aspects of spatial vision in subjects presenting with macular degeneration and visual snow. Emphasis was placed on the effects of aging and/or ocular disease on binocular summation and the measurement of differences between the two eyes in a number of visual tasks. Accommodation performance was measured for both pre-presbyopic and presbyopic observers. The results showed no binocular advantage for either group for far or intermediate stimulus vergences. The effects of visual crowding upon visual acuity were tested using a Landolt C optotype with surrounding distractors. Binocular advantage was found to be higher along the line of sight and to decrease in the near periphery. The presence of distractors reduced visual resolution significantly at every eccentricity, with the effect becoming more pronounced in the periphery. The latter was observed for both monocular and binocular viewing conditions leading to the suggestion that the involvement of binocularly driven neurons may not be essential for visual crowding. The effects of healthy aging and ocular disease on spatial and chromatic vision were also investigated. It was found that stimulus presentation time in a gap acuity task affects visual acuity differently in patients with Age-related Macular Degeneration (AMD) when compared to normal subjects. The processing of briefly presented optotypes appears to be severely reduced in AMD patients. Visual performance was also investigated in patients who experience ‘visual snow’. While gap acuity at any stimulus duration and the strength of chromatic afterimages were found to be unaffected, involuntary pupil recovery following brief exposure to chromatic stimuli was found to be delayed in 3 of the 6 visual snow (VS) patients examined. The absence of a normal pupil recovery is consistent with abnormally slow signals that may also play a part in VS. The novel findings reported in this thesis suggest that advanced vision tests can be used to quantify the effects of normal aging and to detect and monitor the earliest changes in diseases of the eye.