Spatial Patterns of Fixation-Switch Behavior in Strabismic Monkeys



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Investigative Ophthalmology & Visual Science


Purpose: Patients with strabismus perceptually suppress information from one eye to avoid double vision. Mechanisms of visual suppression likely lead to fixation-switch behavior wherein the subject acquires targets with a specific eye depending on target location in space. The purpose of this study was to investigate spatial patterns of fixation-switch behavior in strabismic monkeys. Methods: Eye movements were acquired in three exotropic and one esotropic monkey in a binocular viewing saccade task. Spatial patterns of fixation were analyzed by calculating incidence of using either eye to fixate targets presented at various gaze locations. Results: Broadly, spatial fixation patterns and fixation-switch behavior followed expectations if a portion of the temporal retina was suppressed in exotropia and a portion of the nasal retina was suppressed in esotropia. Fixation-switch occurred for horizontal target locations that were approximately greater than halfway between the lines of sight of the foveating and strabismic eyes. Surprisingly, the border between right eye and left eye fixation zones was not sharply defined and there was a significant extent (>10°) over which the monkeys could acquire a target with either eye. Conclusions: We propose that spatial fixation patterns in strabismus can be accounted for in a decision framework wherein the oculomotor system has access to retinal error information from each eye and the brain chooses between them to prepare a saccade. For target locations approximately midway between the two foveae, strength of retinal error representations from each eye is almost equal, leading to trial-to-trial variability in choice of fixating eye.



Eye movements, Strabismus, Monkeys, Visual suppression, Visual fixation


Copyright 2014 Investigative ophthalmology & visual science. Recommended citation: Agaoglu, Mehmet N., Stephanie K. LeSage, Anand C. Joshi, and Vallabh E. Das. "Spatial patterns of fixation-switch behavior in strabismic monkeys." Investigative ophthalmology & visual science 55, no. 3 (2014): 1259-1268. DOI: 10.1167/iovs.13-13460. URL: Reproduced in accordance with the original publisher’s licensing terms and with permission from the author(s).