Rebound nystagmus: EOG analysis of a case with a floccular tumour.

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Abstract
Eye movements were recorded and quantitatively analyzed in a patient with a tumor initially involving the cerebellar flocculus. Ocular motor abnormalities included impaired smooth pursuit, impaired cancellation of the vestibulo-ocular reflex when fixating an object rotating with the head, and gaze paretic and rebound nystagmus. Comparable findings were reported in monkeys with experimental floccular lesions. The rebound nystagmus (but not the other ocular motor abnormalities) disappeared when the tumor appeared to invade the brain stem in the region near the vestibular nuclei. Apparently, the floccular lesion unmasked a bias which created rebound nystagmus; the bias probably arose in the vestibular nuclei.