Three-Dimensional Kinematics Of Ocular Drift In Humans With Cerebellar Atrophy. D. Straumann1,2, D.S. Zee1,3, D. Solomon1. 1Department of Neurology, Johns Hopkins Hospital, Baltimore, USA; 2Department of Neurology, Zurich University Hospital, Switzerland; 3Departments of Ophthalmology and Otolaryngology -- Head and Neck Surgery, Johns Hopkins Hospital, Baltimore, USA.
APStracts 6:0515N, 1999.
The cerebellar ocular motor syndrome includes the inability to hold horizontal and vertical fixation. Typically, in the presence of a cerebellar atrophy, the eyes show horizontal gaze-evoked and vertical downbeat nystagmus. We asked whether, in addition, the cerebellar ocular motor syndrome includes a torsional drift, and specifically if it is independent from the drift in the horizontal-vertical plane. The existence of such a torsional drift would suggest that the cerebellum is critically involved in maintaining the eyes in Listing's plane. Eighteen patients with cerebellar atrophy (diagnosis confirmed by magnetic resonance imaging) were tested and compared to a group of normal subjects. Three-dimensional eye movements (horizontal, vertical, torsional) during attempted fixations of targets at different horizontal and vertical eccentricities were recorded by dual search coils in a three-field magnetic frame. The overall ocular drift was composed of an upward drift that increased on lateral gaze, a horizontal centripetal drift that appeared on lateral gaze, and a torsional drift that depended upon horizontal eye position. The vertical drift consisted of two subcomponents: a vertical gaze-evoked drift, and a constant vertical velocity bias. The increase of upward drift velocity with eccentric horizontal gaze was due to an increase of the vertical velocity bias; this component did not comply with Listing's law. The horizontal-eye-position-dependent torsional drift was intorsional in abduction and extorsional in adduction, which led to an additional violation of Listing's law. The existence of torsional drift that is eye-position-dependent suggests that the cerebellum is critically involved in the implementation of Listing's law, perhaps by mapping a tonic torsional signal that depends on the direction of the line-of-sight. The magnitude of this signal might reflect the difference in torsional eye position between the torsional resting position determined by the mechanics of the eye plant and the torsional position required by Listing's law.
Received 23 June 1999; accepted in final form 8 October 1999.
APS Manuscript Number J510-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999