Testing the effect of dichoptic surround masking in amblyopic vision

Amblyopia is a neurodevelopmental disorder of spatial vision. Individuals with amblyopia exhibit persistent deficits in their amblyopic eye as a result of strong intraocular suppression from the fellow eye. We previously found that a dichoptic surround mask (mask to one eye, test to the other) improved contrast sensitivity in the eye of two observers exhibiting a deficit in low spatial frequency contrast sensitivity. Our aim was to determine if a similar improvement in contrast sensitivity from dichoptic surround masking might occur in amblyopia. We employed a dichoptic surround masking paradigm. Subjects’ task was to detect the presence of a central target in a two interval-forced-choice procedure. Stimuli were horizontally oriented 0.5 cpd gratings. The central test stimulus was 2 degrees and the surround mask 6.5 degrees in diameter. There were two interleaved test conditions, one to the amblyopic eye the other to the fellow eye, and three surround mask conditions: no mask, same eye mask and test and opposite eye mask and test, giving a total of six conditions. We found that contrast thresholds in the amblyopic eye were elevated in both same eye mask/test and opposite eye mask/test conditions, but to a greater extent in the opposite eye mask/test condition. In summary, dichoptic surround masks failed to improve contrast sensitivity in the amblyopic eye. The amblyopic eye is more susceptible than the fellow eye to the effects of surround masking, irrespective of whether the mask and test are presented to the same or to opposite eyes.