Vertical ocular dysmetria--vertical rebound nystagmus and optokinetic vertical ocular dysmetria.

Ocular dysmetria in vertical eye movement was confirmed by electronystagmographic recording in 100 cases. Ocular dysmetria in spontaneous vertical ocular movement was reported in seven cases. It can be called vertical rebound nystagmus. This phenomenon was more prominent in vertical movement of the eyes returning from upward gazing to mid-position than in the movements of downward gazing. Optokinetic vertical ocular dysmetria induced by vertical optokinetic stimulation was observed in 93 cases. This phenomenon was far more prominent in upward optokinetic nystagmus than in downward optokinetic nystagmus. The pattern of optokinetic vertical ocular dysmetria was classified into the following four types: the dysrhythmic type, the overshoot type, the ataxic type and the saccadic (semi-inversive) type. The pathophysiological mechanism of horizontal ocular dysmetria should be different from the mechanism of vertical ocular dysmetria.