Eye-Movement Responses to Disparity Vergence Stimuli with Artificial Monocular Scotomas

The effects of artificial monocular scotomas on eye-movement responses to horizontal disparity vergence stimuli were studied in six subjects with normal binocular vision. Subjects viewed stereoscopic 1.5° horizontal step disparity vergence stimuli through liquid crystal shutter glasses. The central portion of the stimulus presented to the right eye was removed to simulate monocular artificial scotomas of variable diameters (2° to 10°). Eye movements were recorded with a binocular head-mounted eye tracker. Responses included pure vergence, vergence followed by saccades, and pure saccadic eye movements. The rate of responses with saccadic eye movements increased with the diameter of the artificial scotoma (p < 0.0001); there was an increase in the rate of responses starting with saccades (p < 0.0001), as well as an increase in the rate of saccades after initial vergence responses (p < 0.01). The probability of saccades after initial vergence responses was affected by the open-loop gain of the vergence response (p < 0.001). The open-loop gain decreased with increased diameters of the artificial scotomas (p < 0.0001). As the diameter of the artificial scotomas increased, the amplitude of the initial vergence eye-movement responses decreased, and the prevalence of saccadic eye movements and asymmetric vergence increased. The effects of the diameter of artificial monocular scotomas on eye-movement responses in subjects with normal binocular vision are consistent with the effects of diameter of suppression scotomas on eye-movement responses to disparity vergence stimuli in patients with infantile esotropia.