Slow and Fast Phase Velocities of Optokinetic Nystagmus Induced by the Optokinetic Pattern Test in Infratentorial Lesions

Abstract

Optokinetic pattern (OKP) abnormalities in 36 patients with infratentorial lesions confirmed by CT or MRI were analyzed by microcomputer. the computer analysis system enabled the OKP data to be changed to digital data consisting of the slow phase velocity (S-VEL) and the fast phase velocity (F-VEL) in optikinetic nystagmus. in 16 patients with acoustic tumors. S-VELs were normal or borderline when the tumors were less than 2 cm in diameter, but when the tumors were more than 2 cm, S-VELs were severely impaired. F-VEL abnormalities were not seen in our study except in one patient. in 20 patients with brain stem and/or cerebellar lesions, S-VELs were abnormal in all the patients with the exception of 3. There was no significant difference in S-VEL between the group with brain stem lesions and that with cerebellar lesions. F-VEL abnormalities were seen in only 4 patients with brain stem lesions, especially pontine lesions. These findings suggest that S-VEL is a sensitive indicator for infratentorial lesions and F-VEL an important indicator for pontine lesions.

Key Words:

• optokinetic pattern test (OKP)
• computer analysis
• acoustic and CP angle tumors
• brain stem lesion
• cerebellar lesion