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Decorrelation of Cerebral Visual Inputs as the Sufficient Cause of Infantile Esotropia

¹ From the Departments of Ophthalmology and Visual Sciences,
² Pediatrics, Anatomy and Neurobiology
³ Washington University Medical Center, St. Louis, Missouri;
⁴ Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Ontario
⁵ Departments of Ophthalmology and Neurology, University of California, Los Angeles, California
⁶ the Yerkes Regional Primate Center, Atlanta, Georgia

Background and Purpose: Human infants at greatest risk for esotropia are those who suffer cerebral insults that could decorrelate signals from the two eyes during an early critical period of binocular, visuomotor development. The authors reared normal infant monkeys under conditions of binocular decorrelation to determine if this alone was sufficient to cause esotropia, and associated behavioral as well as neuroanatomic deficits.

Methods: Binocular decorrelation was imposed using prism-goggles for durations of 3–24 weeks (control monkeys wore plano goggles), emulating unrepaired strabismus of durations 3 months to 2 years in human infants. Behavioral recordings were obtained, followed by neuroanatomic analysis of ocular dominance columns and binocular, horizontal connections in the striate visual cortex (area V1).

Results: Concomitant, constant esotropia developed in each monkey exposed to decorrelation for a duration of 6–24 weeks. The severity of ocular motor signs (esotropia angle; dissociated vertical deviation; latent nystagmus; pursuit / optokinetic tracking asymmetry; fusional vergence deficits), and the loss of V1 binocular connections increased as a function of decorrelation duration. Stereopsis was deficient and motion visually evoked potentials were asymmetric. Monkeys exposed to decorrelation for 3 weeks showed transient esotropia, but regained normal alignment, visuomotor behaviors, and binocular V1 connections.

Conclusions: Binocular decorrelation is a sufficient cause of infantile esotropia when imposed during a critical period of visuomotor development. The systematic relationship between severity of visuomotor signs and severity of V1 connectivity deficits provides a neuroanatomic mechanism for these signs. Restoration of binocular fusion and V1 connections after short durations of decorrelation helps explain the benefits of early strabismus repair in humans.

Key words: strabismus, visual cortex, eye movements, stereopsis, extraocular muscles