The fast-phase velocity of optokinetic nystagmus in central nervous system disorders.

The fast phase of optokinetic nystagmus (OKN) in patients with central nervous system (CNS) disorders was quantitatively evaluated using a micro-computer. The relationship between peak velocity of the fast phases of OKN (velocity(p] versus amplitude was recognized to be best fitted to an exponential equation, i.e., velocity(p) = K(1-exp[-amplitude/L]). In patients with lesions in thalamus, midbrain, or pons, the velocity(p) was significantly reduced, whereas in patients with lesions in the medulla or the cerebellum, it was normal. The directional asymmetry of velocity(p) toward the lesion side indicated that the velocity(p) toward the intact side was significantly reduced as compared with that toward the lesion side in patients with lesions in the thalamus or midbrain, whereas in patients with lesions in the pons, the velocity(p) toward the lesion side had decreased significantly as compared with that toward the intact side. Thus the quantitative evaluation of velocity(p) may provide some important information on the mapping of lesions in patients with CNS disorders.