Could Different Smooth Pursuit and Saccadic Abnormalities in Spinocerebellar Ataxia Type 3 (SCA3) Be Explained by a Single Deficient Mechanism? (P02.259)

Abstract

Objective: To evaluate smooth pursuit and saccade characteristics in SCA3 while trying to reveal if different abnormalities could be explained by a single mechanism. Background Different types of eye movement abnormalities are frequently found in the clinical examination of patients with SCA3. However, an objective documentation of those abnormalities using precise measures of eye movements is relatively scarce. Design/Methods: Smooth pursuit and saccadic eye movements were recorded in nine SCA3 patients and two controls using a scleral search coil system. Results: All SCA3 patients have jerky pursuit gain and abnormal saccades. Abnormal saccades were of two types: three patients have a low peak velocity, while the other six patients have normal peak velocity but have a significant occurrence of pathological dynamic overshoot, that is a small saccade that follows the main saccade, in the opposite direction, with no delay. This dynamic overshoot was not clinically detectable and different from hypermetric (position) overshoot saccades in which a corrective saccade that follows a main saccade is initiated after the eye comes to a complete rest. Conclusions: Saccadic dynamic overshoot is frequent in SCA3. Using models from engineering control systems, we hypothesize that a lack of velocity feedback in SCA3 patients can explain the measured abnormalities in smooth pursuit as well as the slow saccades and frequent dynamic overshoots. These results could be of significance in the search of new clinical neurophysiological biomarkers. Disclosure: Dr. Gordon has nothing to disclose. Dr. Zivotofsky has nothing to disclose. Dr. Caspi has nothing to disclose.