Ultralow vestibuloocular reflex time constants.
We report detailed oculomotor studies in 3 patients with central nervous system lesions and markedly decreased time constants (less than 2 seconds) of the vestibuloocular reflex (VOR). In 1 patient with Chiari type I malformation, serial measurements over 3 years documented a progressive decrease in the duration of postrotatory nystagmus (100 deg/sec steps, acceleration 140 deg/sec2) until finally there was no sustained nystagmus. At this time, the patient had no response to caloric stimulation or to sinusoidal rotation below 0.2 Hz but normal gain (peak slow-phase eye velocity/peak chair velocity) above 0.4 Hz (phase lead increased). Gaze holding, saccades, smooth pursuit, and optokinetic nystagmus were normal, but optokinetic-after-nystagmus disappeared. The other 2 patients (combined brainstem-cerebellar atrophy) had impaired gaze holding, abnormal smooth pursuit and optokinetic nystagmus, and absent optokinetic-after-nystagmus. VOR gain to step and high-frequency sinusoidal stimuli was increased. The neural mechanism that normally prolongs the VOR time constant may have reduced it in our patients.
Baloh
R W
RW
Department of Neurology, California at Los Angeles School of Medicine 90024-1769.
Beykirch
K
K
Tauchi
P
P
Yee
R D
RD
Honrubia
V
V
D000328:Adult; D001139:Arnold-Chiari Malformation / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D009760:Nystagmus, Physiologic; D009801:Oculomotor Muscles / Q000503:physiopathology; D009849:Olivopontocerebellar Atrophies / Q000503:physiopathology*; D012027:Reflex, Vestibulo-Ocular; D013132:Spinocerebellar Degenerations / Q000503:physiopathology*; D013997:Time Factors