1. Disconjugate Optokinetic Tracking in Normal and Strabismic Infant and Adult
Monkeys
Alexandre Amice and Lawrence Tychsen, M.D.
Departments of Ophthalmology, Pediatrics, Anatomy and Neurobiology
Washington University Medical Center, St Louis MO
Introduction: The purpose of this study was to assess how strabismus affects vergence
error in monkeys during OKN. Vergence error should decrease as a monkeys’ age
increases and should be more pronounced in monkeys with strabismus due to the pre-
existing condition of misaligned eyes. Methods: Horizontal OKN and vergence were
measured using the magnetic scleral search coil technique in normal adult monkeys,
normal infant monkeys, and infant monkeys who developed strabismus due to prism
rearing. The vergence angle was calculated during the slow-phase of OKN in both
monocular and binocular viewing to determine the magnitude of disconjugacy during
stimulus motion. Results: In binocular viewing the vergence error in all the monkeys
tended to be less than when one eye was occluded. The normal adult monkey’s vergence
error was negligible, with the average divergence of the eyes ≤ 0.3 degrees in binocular
viewing. The strabismic infant monkey had a higher error; the eyes diverging an average
2.7 degrees in binocular viewing and 3.4 degrees in monocular viewing. Normal infant
monkey had vergence error greater than normal adult but less than the strabismic animals
(an average 2.27 degrees in monocular viewing). Conclusion: As a normal monkey’s age
increases, their eyes tend to diverge less – move more conjugaetly -- during OKN.
Strabismus impairs accurate eye movements, increaseing the amount of disconjugacey
during tracking.