A study of congenital nystagmus: vestibular nystagmus.

The vestibulo-ocular response (VOR) to rotatory stimuli was studied by electro-oculography in 41 patients with congenital nystagmus. The pattern of the VOR and the gain of the slow component velocity (peak eye velocity/peak chair velocity) were normal in 55 per cent of the patients. In 10 per cent of patients an abnormal pattern of the VOR in which the eyes deviated tonically in the direction of the slow component of the VOR was found. In these patients a mild defect in the generation of vestibular fast components might be present since the slow component velocity (SCV) appeared to be normal, but the amplitude and frequency of fast components were decreased. Thirty-two per cent of patients demonstrated persistence of an intense nystagmus with eyes opened in the dark. However, summation of the smooth movement velocity of the nystagmus and the SCV of a probably normal VOR could be demonstrated. The VOR was basically normal in patients with congenital nystagmus with or without associated ocular lesions.