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Suraj Upadhyaya, Hui Meng, Vallabh E Das; Electrical Stimulation of the rostral Superior Colliculus in Strabismic Monkeys alters Strabismus Angle.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Disruption of binocular vision during the early critical period leads to eye misalignment in humans and in macaque monkey models. A recent study in normal monkeys has demonstrated vergence related activity in the rostral part of the Superior Colliculus (SC) and electrical stimulation in this area leads to divergence and convergence eye movements when looking at a near target. The purpose of our study was to determine the role of the rostral Superior Colliculus in maintaining eye misalignment in strabismic monkeys.
Three juvenile optical prism-reared strabismic monkeys previously trained in oculomotor tasks were used as a model of developmental strabismus in this study. Electrical stimulation was delivered to the intermediate and deep layers of the rostral Superior Colliculus via the recording microelectrode (400Hz, 0.5s duration, 20-50uA). Scleral search coils were used to record movements of both eyes. The goal of the analysis was to examine changes in alignment and conjugacy of saccades during electrical stimulation.
Electrical stimulation in the rSC resulted in small amplitude (<5deg) staircase saccades with both horizontal and vertical components as predicted from the topographic map within the Superior Colliculus. Electrical stimulation of rostral sites also resulted in changes in horizontal strabismus angle, i.e., a shift towards exotropia/esotropia (4/6 sites divergent change; 2/6 sites convergent change). Although electrical stimulation frequently leads to saccades with both horizontal and vertical components, i.e., oblique saccades, there was minimal change in vertical misalignment. The change in misalignment was due to a combination of disconjugate saccades and post-saccadic drift. The saccade disconjugacy was relatively small compared to the change in misalignment in 4/6 sites (ratio of amplitude of saccade disconjugacy to change in alignment < 0.3). Further saccade disconjugacy and the final change in misalignment were sometimes in opposite directions and not consistently related to the amplitude of the saccade.
Electrical stimulation of rostral Superior Colliculus of strabismus monkeys produces a change in horizontal eye alignment and disconjugate saccadic eye movements. The mechanisms for saccade disconjugacy and change in alignment due to rSC stimulation may be different.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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