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Suraj Upadhyaya, Vallabh Das; Properties of cells associated with strabismus angle in the rostral superior colliculus of strabismic monkey. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1021.
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© ARVO (1962-2015); The Authors (2016-present)
Disruption of binocular vision during the critical period for development leads to eye misalignment in humans and in monkey models. Fixation stability is poor in strabismic humans and monkeys. We have previously shown that electrical stimulation of the superior colliculus (SC) in strabismic monkeys changes strabismus angle. The purpose of this study was to investigate the response properties of cells associated with eye misalignment in the SC of strabismic monkeys.
One adult optical prism-reared strabismic monkey was used in this study. Scleral search coils were used to measure movements of both eyes during fixation and saccade tasks at a distance of 57cm. Single cell recording within the rostral portion of the SC was performed with epoxy-coated tungsten electrodes. The goal of the neural analysis was to examine relationship of SC firing with eye alignment. In control experiments, visual sensitivity of these cells was examined by blanking out the target for 400ms during fixation.
28 cells with responses correlated with change in eye misalignment were recorded from the rostral part of the SC of the strabismic monkey. 17 cells showed increased responses for smaller angles of exotropia (near response cells - NRC) and 11 cells showed increased responses for larger angles of exotropia (far response cells - FRC). Population sensitivity of NRC (3.24±1.62 spks/sec/°) and FRC (-3.10±1.80 spks/sec/°) were similar to that of convergence and divergence cells found previously in the rostral SC of normal monkeys. However, thresholds were different between strabismic (NRC: -18.28° and FRC: 3.82°) and normal monkeys (NRC: ~0°; FRC: ~15°). 21/25 of the cells showed a decrement (>20%) in firing during saccades. Only 2/18 cells showed a decrement (>20%) in firing during target blank testing.
SC cells previously identified as being related to vergence in normal monkeys show responses related to eye misalignment in strabismic animals. The change in threshold (shift towards exotropia) in exotropic strabismic compared to the normal suggests that this structure is contributing to the maintenance of strabismus angle.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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