Case of downbeat nystagmus influenced by otolith stimulation.

A patient with downbeat nystagmus and familial ataxia is described. The nystagmus was induced by static tilt away from normal upright posture, by linear acceleration of the head, and by convergence. It is inferred that the nystagmus was modulated by otolith-specific stimuli and not by stimulation of the canals. These findings demonstrate the role of otolith function in generation of eye movements in the vertical plane and support proposed interrelationships between otolith and vergence mechanisms. The nystagmus and associated oscillopsia were partially suppressed by treatment with clonazepam.