Clinical suppression and amblyopia.

In individuals with abnormal binocular vision, such as strabismics and anisometropes, it is common for all or part of one eye's view to be suppressed so binocular confusion and diplopia are eliminated. We examined the relation between the depth of suppression (the amount by which the monocular contrast increment threshold for an eye was elevated by stimulation in the contralateral eye) and the degree of amblyopia (difference in monocular contrast thresholds for the two eyes). There was a significant negative correlation between suppression and amblyopia, so that clinical suppressors with no amblyopia exhibited deep suppression (ie, large threshold elevation) while observers with amblyopia exhibited weaker or no suppression. This negative correlation was found when the two eyes viewed orthogonally oriented contours as well as identically oriented contours. These results suggest that when an eye is amblyopic there is no longer a need for strong suppression of that eye by the contralateral eye.