Disjunctive optokinetic nystagmus in a naturally esotropic macaque monkey: interaction between nasotemporal asymmetries of versional eye movement and convergence.
OBJECTIVE
To assess the interaction between versional and vergence eye movements in normal and strabismic monkeys.


METHODS
Horizontal optokinetic nystagmus (OKN) and vergence were measured using the magnetic scleral search coil technique in a normal adult monkey and a strabismic monkey who had naturally occurring early-onset esotropia. Mean eye velocity and vergence angles were calculated during the slow phases of OKN.


RESULTS
The strabismic monkey 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 eye. The velocity of the abducting eye was between 55 and 80% of the velocity of the adducting eye (p < 0.01). As a consequence of the disjunctive movements, the eyes converged an average of 4 +/- 2.8 degrees during OKN. Saccadic analysis documented normal lateral rectus function in each eye. Neither an OKN asymmetry nor disjunctive OKN was observed in the normal monkey.


CONCLUSIONS
Disjunctive OKN in the esotropic monkey suggests that the cerebral maldevelopment responsible for nasally biased OKN also contributes to nasal biases in vergence pathways.
Yildirim
C
C
Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA. yildirimc@hotmail.com
Tychsen
L
L
D000818:Animals; D002490:Central Nervous System / Q000503:physiopathology; D003290:Convergence, Ocular / Q000502:physiology*; D004558:Electric Stimulation; D004948:Esotropia / Q000503:physiopathology / Q000662:veterinary*; D008253:Macaca mulatta; D008280:Magnetics; D008992:Monkey Diseases / Q000503:physiopathology*; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D009801:Oculomotor Muscles / Q000294:innervation / Q000503:physiopathology; D012438:Saccades / Q000502:physiology*; D015349:Vision, Monocular / Q000502:physiology