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Paul E. Foeller, Agnes Wong, Dolores Bradley, Lawrence Tychsen; A Primate Model of Intermittent Exotropia. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6356.
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Non-human primates with esotropic strabismus have been shown to be accurate animal models of human infantile esotropia. Intermittent exotropia is also a common subtype of human strabismus, but adequate primate models have been lacking. Here we report early-onset intermittent exotropia in macaque monkeys.
Perceptual and eye movement testing was conducted on 2 monkeys who had onset of exotropia at age 6 mons - 2 yrs. Binocular search coil ocular motor recordings were obtained at near and far cardinal gaze positions to test for pattern deviation or incomitance. Liquid crystal shutter goggles were used for single/alternate cover testing. Visual acuity was tested using SSVEPs.
The monkeys showed orthotropic fusion under conditions of unimpeded binocular viewing, interrupted by episodes of comitant, alternating heterotropia. Cover testing elicited exodeviations of 5 -17 deg, which in one animal replicated a pseudo-divergence excess pattern. One animal also displayed small DVDs, as observed in a subset of human patients with intermittent exotropia. Vergence, saccadic and vestibulo-ocular reflex testing revealed no evidence of brainstem dysfunction or extraocular muscle paresis. The animals alternated fixation when heterotropic and had normal visual acuity in each eye with no substantial refractive errors.
Intermittent exotropia is less common than esotropia in non-human primates, as in humans. The ocular motor behavior of these animals closely mimics that of exotropic children and adults, providing a promising animal model for invasive studies of underlying mechanisms.
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