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P<P, published online ahead of print May 9, 2008
(Investigative Ophthalmology and Visual Science. )
© 2008 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.08-1699
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Article

The effect of acute superior oblique palsy on vertical pursuit in monkeys

Jing Tian 1, Xiaoyan Shan 1, Howard Ying 2, Mark F Walker 1, Rafael J Tamargo 3, and David S. Zee 1*

1 Neurology, The Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States
2 Ophthalmology, The Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States
3 Neurosurgery, The Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States

* To whom correspondence should be addressed. E-mail: dzee{at}dizzy.med.jhu.edu.


  Abstract

Purpose: To investigate vertical smooth pursuit eye movements in monkeys with acute acquired superior oblique palsy (SOP). Methods: The trochlear nerve was severed intracranially in two rhesus monkeys. After surgery, the paretic eye was patched for 6 or 9 days, and then binocular viewing was allowed. Eye movements were measured with binocular, dual search coils, before and after surgery, under monocular viewing conditions. Vertical pursuit movements along the midline were elicited using triangular-wave (20°/s, ±20°) or step-ramp (20°/s) stimuli at a distance of 66 cm. Results: During the early post-lesion period, before binocular viewing was allowed, pursuit velocity of the paretic eye during triangular-wave tracking was lower than that of the normal eye. When the viewing eye crossed straight ahead, the changes in pursuit velocity conjugacy were similar for upward and downward tracking. After habitual binocular viewing was allowed differences between upward and downward pursuit emerged. When measured ~30 days post-lesion this directional asymmetry was less during the open-loop period of step-ramp tracking than during triangular-wave tracking. Conclusions: Rhesus monkeys with acute acquired SOP show characteristic changes in vertical pursuit, with deficits for both upward and downward tracking, and differences between the initiation of step-ramp pursuit and the sustained response during triangular-wave tracking. The habitual viewing condition (monocular vs. binocular) also affected the pattern of deficit.

Key Words: eye movements, smooth pursuit, strabismus






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