Two patients with hereditary spinocerebellar degeneration with slow eye movements were examined with electronystagmography.
The results in case 1 were as follows:
a. Pursuit eye movements were intact in all directions.
b. Rapid eye movements were disturbed in both vertical and horizontal directions. Horizontal eye movements showed slower velo-city than vertical ones.
c. Optokinetic nystagmus (OKN) in the horizontal direction showed a square wave pattern without a fast component.
d. In caloric tests, oscillatory eye movements were recorded during irrigation of both ears. In the visual suppression test, decreased fixation suppression was observed with cold water irrigation of the left ear, while normal fixation was obtained with irrigation of the right ear.
e. Upward nystagmus was elicited by bilateral irrigation with cold water.
The results in case 2 were as follows:
a. The velocity of rapid eye movements decreased, especially in the horizontal direction.
b. The fast phase of, OKN was absent except for upward OKN.
c. In caloric tests with cold water, the eyes deviated to the stimulated side.
A review of the literature suggests that the site of lesions responsible for slow eye movements is the paramedian pontine reticular formation or its afferent fibers.
