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Cerebellar skew deviation and the torsional vestibuloocular reflex

From the Department of Ophthalmology and Vision Science and the Division of Neurology, University Health Network, University of Toronto, Ontario, Canada.

Address correspondence and reprint requests to Dr. Agnes Wong, Elm Wing S102D, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8; e-mail: agnes.wong{at}utoronto.ca

Background: Skew deviation is typically caused by brainstem damage, and has not been identified with focal cerebellar lesions. This vertical strabismus has been attributed to asymmetric disruption of vestibuloocular reflex (VOR) projections from otolithic receptors of the utricle to ocular motoneurons, but asymmetry of the utriculo-ocular counter-roll reflex has not been detected.

Methods: Lesions localized to the cerebellum were identified by MRI in five patients with vertical strabismus. Their skew deviation was measured by prism cover tests in all patients and by search coils in three patients. The angular VOR was tested in patients and 10 controls during sinusoidal ± 10 degree torsional, vertical, and horizontal head-on-body rotations at 0.5, 1, and 2 Hz. Static torsional VOR gain was measured by the change in torsional eye position divided by change in head position during maintained head tilt.

Results: Static torsional VOR gains were asymmetric in each patient. Three patterns of asymmetry were identified: 1) decreased static gain in one eye in both directions; 2) decreased gains in both eyes in one direction; and 3) asymmetric gain in one direction in one eye alone. Dynamic torsional VOR gains were symmetrically reduced in both directions in both eyes in all patients.

Conclusions: Focal cerebellar lesions can cause skew deviation. The static torsional vestibuloocular reflex (VOR) is linked to cerebellar control of vertical vergence. Asymmetry between the eyes or in direction of the static torsional VOR provides evidence that monocular or binocular imbalance of the utriculo-ocular reflex leads to cerebellar skew deviation.

Additional material related to this article can be found on the Neurology Web site. Go to www.neurology.org and scroll down the Table of Contents for the August 9 issue to find the title link for this article.

Supported by the New Investigator Award (MSH 55058) (A.W.) and grants MT 5404, ME 5509 (J.A.S.), MOP 57853 (A.W. and J.A.S.), and MOP 67104 (A.W.) from the Canadian Institutes of Health Research (CIHR), and the University Health Network Ophthalmology (A.W.) and Neurology (J.A.S.) Practice Plans.

Disclosure: The authors report no conflicts of interest.

Received November 11, 2004. Accepted in final form April 12, 2005.

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