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D Yang, EJ FitzGibbon, FA Miles; Effects of Real and Simulated Tropias on Human Short-Latency Disparity Vergence . Invest. Ophthalmol. Vis. Sci. 2002;43(13):962.
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Purpose: To obtain evidence for anomalous retinal correspondence by determining the range of horizontal disparities over which normal and strabismic patients show short-latency vertical disparity vergence responses to vertical disparity steps. Methods: Subjects faced a large tangent screen onto which two identical random-dot patterns were back-projected. A system of crossed polarizers ensured that each eye saw only one of the patterns. Mirror galvanometers were used to control the horizontal and vertical positions of the images independently. Step changes in horizontal and/or vertical disparity were applied 50 ms in the wake of a centering saccade to take advantage of post-saccadic enhancement. The electromagnetic search-coil technique was used to record the movements of both eyes in 3 normal subjects, and in one esotrope with no prior history of eye surgery who had 20/20 acuity O.U. but no binocular vision on the Worth 4-dot and Titmus stereo tests. Her tropia in our near-viewing setup was about 6 deg. Results: Vertical disparity steps induced vertical vergence eye movements at latencies of 80-100 ms in all subjects. Based on the change in vertical vergence over the period 90 to 157 ms after the onset of the step, these responses peaked with vertical disparity steps of 0.8-1.6 degrees. Responses were weaker in the esotrope (who also showed much weaker-than-normal horizontal vergence eye movements to horizontal disparity steps). For all subjects, the vertical vergence responses to a given vertical disparity step were reduced if horizontal disparity was also introduced (simulated horizontal tropia). Further, for all subjects, 6 deg of imposed horizontal disparity (crossed or uncrossed) was sufficient to totally eliminate the vertical vergence responses to vertical disparity. This means that the esotrope was behaving like a normal subject despite her 6 deg of esotropia, and so was responding maximally to vertical disparities while actually experiencing a horizontal (uncrossed) disparity of 6 degrees: anomalous retinal correspondence. Conclusions: Short-latency disparity-vergence responses are useful for the study of binocular vision and have provided objective evidence for anomalous retinal correspondence in an esotrope. Supported by: The National Eye Institute
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