The Torsional Vestibulo–Ocular Reflex in Patients With Skew Deviation Caused by Focal Cerebellar Lesions

Abstract

Abstract: : Purpose: Neuropathological or imaging evidence of focal cerebellar lesions as a cause of skew deviation is lacking. Skew deviation has typically been attributed to asymmetric brainstem disruption of otolithic projections to the ocular motor nuclei. We identify skew deviation from focal lesions of the cerebellum and quantify roles of the vestibulo–ocular reflex (VOR) in its pathogenesis. Methods: Lesions localized to the cerebellum were identified by magnetic resonance imaging in five patients with skew deviation. Strabismus was measured by prism cover tests in each patient and by magnetic search coil oculography in three patients. The angular VOR was tested in darkness and during monocular viewing in light during sinusoidal +/–10 degree torsional, vertical and horizontal head–on–body rotations at 0.5, 1 and 2 Hz. Ten normal subjects served as controls. The 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 asymmetrical 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. Effects of cerebellar damage on vertical alignment and static torsion of the eyes reveal roles of the cerebellum in regulating the torsional VOR. Asymmetry between the eyes or in direction in the static torsional VOR provides evidence that monocular or binocular imbalance of the utriculo–ocular reflex leads to cerebellar skew deviation.

Keywords: eye movements • vestibulo-ocular reflex • strabismus