Disorders of eye movement in myotonic dystrophy.

Horizontal saccades and smooth pursuit eye movements were studied in 26 patients with myotonic dystrophy. Clinical neuro-ophthalmological investigations in 1 patient revealed an inability to achieve a full range of eye movements. Electro-oculography showed a significant decrease of the maximum velocity of the visually-guided saccades in 83% of the patients. Smooth pursuit eye movements were not significantly different from age-matched controls. Visual evoked potential (VEP) latencies (P100) were significantly prolonged compared with controls in 64% of the patients. The saccadic latency of the visually-guided saccades was correlated with the prolonged VEP latencies, indicating that lesions in the primary visual pathways probably contribute to the oculomotor dysfunction. The isolated decrease of the maximum velocity of the saccades in combination with EMG findings favours a peripheral (dystrophic) pathophysiological mechanism.