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D. Yang, M. Zhu, M. Kauffman, R. Hertle; Short-Latency Disparity Vergence: Effects of Artificial Scotomas. Invest. Ophthalmol. Vis. Sci. 2007;48(13):886.
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To evaluate binocular motor function in the presence of a monocular suppression scotoma, a condition present in many patients with strabismus, we investigated disparity vergence responses to asymmetric disparity stimuli with varying sizes of monocular artificial scotomas in normal subjects.
Dichoptic disparity stimuli were presented using a mirror haploscope with two computer monitors subtending 40x30 deg at 47 cm from each eye. Random dot patterns were used to deliver disparity. Artificial scotomas were created by placing black circles in the center of one of a pair of the random dot patterns. The stimulus patterns were displayed for 200 ms allowing study of the initial vergence response. Eye movements of both eyes were recorded with a magnetic search coil system. Dynamic properties of vergence and monocular eye movements and relationships between amplitudes of vergence and sizes of scotomas were quantitively analyzed.
Symmetrical vergence (equal monocular response) was induced by disparity stimuli. The addition of a monocular scotoma decreased the amplitude and the amplitude of vergence responses had a direct relationship with scotoma sizes. However, the vergence responses were remain symmetrical (each eye responded equally in amplitudes and latency) irrelevant to scotoma size.
Artificial scotomas caused an impairment of the open-loop vergence responses; however the symmetry of the monocular responses was unaffected. These results suggest that a common control of binocular disparity detectors over ocular motor plant of each eye, which is not in favor of monocular control theory. These data also suggests that patients with strabismus may have damaged vergence systems from both their underlying strabismic disorder and their sensory adaptation to diplopia.
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