[An analysis of slow phase velocity on congenital nystagmus-asymmetrical responses of optokinetic stimulation].

The responses of optokinetic nystagmus (OKN) were examined in 11 patients with congenital nystagmus (CN). When the nystagmus was almost suppressed in a dark room, the OKN stimulation was started. There were three different type of OKN responses: bilaterally reversed OKN, unilaterally, reversed OKN and pendular oscillation. Three of 11 patients had normal direction in the slow phase of OKN in one direction, but reversed OKN in the other direction. These findings suggest that two different directional slow eye movement subsystems (rightward and leftward) exist in CN patients and that the mechanism of CN is unilateral or bilateral dysfunction of the two different directional slow eye movement subsystems.