Disjunctive optokinetic nystagmus in a naturally esotropic macaque monkey:Interaction between nasotemporal asymmetries of versional eye movement andconvergence

Objective: To assess the interaction between versional and vergence eye mov ements in normal and strabismic monkeys, Methods: Horizontal optokinetic ny stagmus (OKN) and vergence were measured using the magnetic scleral search coil technique in a normal adult monkey and a strabismic monkey who had nat urally occurring early-onset esotropia. Mean eye velocity and vergence angl es were calculated during the slow phases of OKN, Results: The strabismic m onkey had a nasotemporal asymmetry of OKN favoring nasally directed motion in each eye. During monocular optokinetic stimulation, mean eye velocities were substantially greater for the adducting as compared to the abducting e ye. The velocity of the abducting eye was between 55 and 80% of the velocit y of the adducting eye (p < 0.01). As a consequence of the disjunctive move ments, the eyes converged an average of 4 +/- 2.8 degrees during OKN, Sacca dic analysis documented normal lateral rectus function in each eye. Neither an OKN asymmetry nor disjunctive OKN was observed in the normal monkey. Co nclusion: Disjunctive OKN in the esotropic monkey suggests that the cerebra l maldevelopment responsible for nasally biased OKN also contributes to nas al biases in vergence pathways. Copyright (C) 2000 S. Karger AG, Basel.