T. C. Hain

Saccades in Huntington's disease: Initiation defects and distractibility

We recorded saccadic eye movements in patients mildly affected with Huntingtons disease. Most showed an increase in saccade latencies that was greater for saccades made on command than to the sudden appearance of a visual target. All patients showed excessive distractibility during attempted fixation. They had particular difficulty suppressing a saccade to a suddenly appearing visual target when simultaneously trying to initiate a saccade in the opposite direction. Our results are compatible with a posited role of the basal ganglia in both the initiation of volitional saccades and in the maintenance of fixation. Saccade abnormalitie—especially distractibility—are sensitive but probably not specific indicators of Huntingtons disease.

Saccades in Huntington's disease: Slowing and dysmetria

Eye movements were recorded from 20 mildly affected patients with Huntingtons disease (HD) who were divided into two groups, 10 patients with onset of symptoms before age 30 and 10 with onset of symptoms after age 30. In the younger onset group (HD < 30), peak saccade velocities were low (<255 deg/sec for 20-deg saccades) in six of the 10 patients, whereas none of the 10 patients in the older onset group (HD > 30) had peak saccade velocities lower than 300 deg/sec. Latencies for volitional saccades were greater than normal in the HD > 30 group, but were normal for the HD < 30 group. The ability to maintain steady fixation in the face of a distracting visual stimulus was decreased, to the same degree, in both groups of HD patients. In addition, 70% of the HD < 30 group had an affected father, while 70% of the HD > 30 group had an affected mother. These findings suggest that the pathophysiology of the slow saccades, initiation deficit, and excessive distractibility in HD are different.

Ipsiversive eye deviation and epileptic nystagmus

We studied an 11-year-old boy with focal seizures in the right temporo-occipital cortex. During the seizure, there was a 1- to 2-second period of ipsiversive (rightward) conjugate eye deviation, followed by 10 to 15 seconds of horizontal jerk nystagmus with slow phases that were directed to the right and appeared linear. The patient was conscious throughout the seizure. These findings fit the description of epileptic nystagmus. We postulate that the eye deviation and slow phases of the nystagmus in this patient were induced by epileptic activation of a cerebral smooth pursuit pathway originating from temporo-occipital cortex.