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Donald MacLeod, Stuart Anstis; Contrast gain control before and after cataract surgery: a case study. Journal of Vision 2016;16(12):388. doi: https://doi.org/10.1167/16.12.388.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Cataracts may greatly reduce the contrast of the retinal image, but the visual consequences of this contrast loss could be mitigated by neural adaptation (provided that the contrast of the stimulus is sufficient for it to be visible at all). We sought evidence for such neural adaptation. Methods: We investigated the suprathreshold perception of contrast, as well as contrast sensitivity, in one observer (author SA). We measured the attenuation of perceived contrast using binocular matches of contrast to reference stimuli viewed by the fellow eye. In addition the contrast differences needed for discrimination at a range of baseline contrast levels were measured in each eye. Such data were collected in the days immediately following surgical cataract removal, starting immediately after the eye patch was removed, as well as pre-operatively. Results: Pre-operatively, suprathreshold stimuli viewed by the cataract eye were judged at least a factor of three higher in contrast than expected on the basis of contrast threshold, so that contrast matches between the two eyes were more accurate than expected on the basis of the threshold difference. This suprathreshold contrast boost persisted post-operatively, so that now gratings could look higher in contrast to the operated eye than to the fellow eye. Contrast discrimination thresholds conformed to Weber's Law, and were similar for the two eyes. Conclusions: The binocular contrast matches reveal a neural 'contrast constancy' process that was able to compensate partly for the optical loss of contrast introduced by the cataract, producing a close approach to accurate contrast matching preoperatively and an 'overshoot' of perceived contrast post-operatively.
Meeting abstract presented at VSS 2016
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