Directional preponderance of optokinetic nystagmus. Study of 30 cases of unilateral cerebral lesions.

Analysis of the optokinetic nystagmus has been one of the most important means to examine the function of the vestibulo-oculomotor system. Especially in Japan, it has been used as a mean to analyze the function of the brain stem. We investigated directional preponderance of the optokinetic nystagmus in supratentorial lesions especially unilateral lesions, in the cerebral hemisphere which had been nearly neglected as an object for investigation of the vestibular system. We examined 30 cases of unilateral lesion in the cerebral hemisphere. In all cases CT-scan confirmed that these lesions have no mass effect which might affect the function of the surrounding brain. It was also confirmed that these cases had no spontaneous nystagmus. These cases consisted of 11 cerebral infarctions, 9 cerebral thrombosis, 6 cerebral hemorrhages and 4 cerebral contusions. In the result, 27 cases showed directional preponderance of the optokinetic nystagmus to the ipsilateral side, while there was none to the contralateral side. Three cases showed no directional preponderance. Some cases showed marked inhibition of optokinetic nystagmus of the contralateral side. These markedly inhibited cases are very similar to cases of pontine lesion which usually manifest marked inhibition of the optokinetic nystagmus to the ipsilateral side.