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.
Department of Neurology, California at Los Angeles School of Medicine 90024-1769.
R W
RW
Baloh
K
K
Beykirch
P
P
Tauchi
R D
RD
Yee
V
V
Honrubia
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