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Contrast gain control before and after cataract surgery; a case study D.I.A. MacLeod* & S. Anstis**

Summary: Contrast gain control before and after cataract surgery; a case study
D.I.A. MacLeod* & S. Anstis**
*E-mail: dmacleod@ucsd.edu, Telephone: (858) 534-3975, Fax: (858) 534-7193.
**E-mail: sanstis@ucsd.edu, Telephone: (858) 534-5456, Fax: (858) 534-7190.
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. 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


Source: Anstis, Stuart - Department of Psychology, University of California at San Diego


Collections: Biology and Medicine