Spontaneous vertical nystagmus.

We reviewed the clinical and oculographic features of 106 patients with spontaneous vertical nystagmus evaluated at the UCLA Eye Movement Laboratories over the past 10 years. Downbeat nystagmus typically occurred with lesions involving the caudal midline cerebellum whereas upbeat nystagmus was most often associated with lesions of the central medulla. Since the vestibular systems is the main source of tonic input to the oculomotor neurons and since the up and down vestibulo-ocular pathways separate beginning at the level of the vestibular nuclei asymmetric involvement of these pathways can explain spontaneous vertical nystagmus.