Fusional vergence eye-movement (VEM) responses to step-disparity visual stimuli were recorded and analyzed in 8 children with infantile esotropia. Unlike subjects with normal binocular vision who generated smooth symmetric VEMs, responses of children with infantile esotropia ranged from saccadic eye-movements (SEMs) to asymmetric VEMs. Using a stereoscopic display system that was developed to simulate suppression scotomas in infantile esotropes, we showed that in subjects with normal binocular vision the magnitude of VEMs decreases and the occurrence of saccades increases as the size of the scotoma increases. This reduction in the magnitude of VEMs as a function of scotoma size is associated with: (a) inaccurate estimates of sensory disparity errors and (b) sub-optimal performance of the closed-loop vergence control system due to interference from the saccadic control system. When the interference of the saccadic control system was reduced in infantile esotropes with large suppression scotomas, their vergence responses were improved substantially.
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