Primary position vertical nystagmus and cerebellar ataxia.

Hereditary cerebellar ataxia was evaluated clinically and by electro-oculography in three members of a family. There was no clinical evidence of exttra-cerebellar dysfunction although quantitative eye movement analysis did shown internuclear ophthalmoparesis and slow saccadic velocity suggestive of brainstem dysfunction. In addition, oculomotor examination showed primary position vertical nystagmus in all patients. Other findings were in accord with previous reports of cerebellar-related oculomotor dysfunction.