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Abstract
Fixation and pursuit movements, movements of regard, of convergence and divergence, and ocular reaction time were recorded electrooculographically in 10 patients with myotonic dystrophy. With the exception of pursuit movements, normal responses were present in 9 out of 10 patients. All of the patients demonstrated a selective and pronounced impairment of pursuit movements which were elicited by a horizontally and sinusoidally moving target. Pursuit movements which are normally smooth were entirely replaced by irregular saccades and gross movements of regard, in both directions of gaze, and irrespective of the target velocity. This selective disturbance of smooth eye movements cannot be explained on the basis of dystrophic changes, or of a myotonic reaction of the extraocular muscles, but is interpreted as evidence for an involvement of the central nervous system in myotonic dystrophy. This view is supported by the associated endocrine and mental changes which occur commonly in this disease, and by previously reported selective disturbances of pursuit movements in association with certain brain lesions.