Purpose Some patients complain of persisting visual noise, often described as “visual snow” (VS) and / or prolonged afterimages, but show no obvious clinical abnormalities. The purpose of this study was to examine the extent to which the processing of different stimulus attributes remains normal in VS patients. Methods Seven VS patients and nine control subjects were examined. Advanced vision and optometric tests were used to assess visual acuity (VA), red / green (RG) and yellow / blue (YB) colour sensitivity, rapid flicker sensitivity, chromatic afterimage strength and duration and pupil response amplitudes and latencies to chromatic stimuli. Results The VS patients exhibited normal VA, colour and rapid flicker sensitivity and chromatic afterimage strength. Both controls and four of the VS patients exhibited pupil constrictions to the onset of the coloured stimulus, followed by recovery during the stimulus and a further constriction at stimulus offset, normally attributed to perception of chromatic afterimages (Prog.Brain Res. 144:243‐259, 2004). The pupil responses in three of the VS patients lacked the rapid recovery phase following the initial constriction to stimulus onset. Conclusion The absence of recovery following the initial constriction of the pupil in three of the VS patients deviates from normal responses and suggests the presence of a more sustained retinal afferent signal that drives the pupil response. The latter may be linked to differences in retinal processing of visual signals that cause the perception of visual snow when the coloured stimulus is viewed against a uniform background.
No abstract
Purpose When a person is confronted with a bright light source against a dim background, scattered light can cause visual discomfort in addition to reducing object contrast on the retina. Previous work addressing the effect of glare on visual performance has focused mainly on the reduction in retinal image contrast (known as disability glare) rather than the often accompanying experience of discomfort glare. This study examines how parallel processing of visual information is affected under conditions of discomfort glare. Methods Light scatter sources surrounded a monitor on which the subject carried out standard contrast acuity (CA) tasks. All CA tasks were carried out with and without discomfort glare (estimated in a prior experiment). In the parallel task, a fovea target (Landolt C) and four peripheral stimuli (three distractors and one target) were presented concurrently; the subject had to indicate both the orientation of the gap for the foveal target and the quadrant containing the peripheral target. The size of the peripheral target was increased relative to the foveal target to ensure that all targets were equally detectable. This was done separately with and without discomfort glare, thus negating any influence of disability glare. Results The presence of discomfort glare degrades visual performance in the parallel processing task even when adjustments are made to cancel out the effects of disability glare. Conclusion Studies that have focused only on disability glare may be underestimating the adverse effect glaring light sources can have on visual performance, particularly in real world scenarios where attention to objects in both the fovea and periphery is often required.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.