MODIFICATION OF PARAMETERS IN VERTICAL OPTOKINETIC NYSTAGMUS AFTER REPEATED VERTICAL OPTOKINETIC STIMULATION IN PATIENTS WITH VESTIBULAR LESIONS

Eye movements were recorded in patients with unilateral and bilateral vestibular lesions after upward and downward optokinetic (OK) stimulat ion before and following 6 weeks' repeated exposure to OK stimulation. In control subjects there was no asymmetry between upward and downwar d slow-phase velocity (SPV). Before training, less subjects showed tha t upward and downward SPV was significantly lower than that of control s. There was no asymmetry between upward and downward SPV. After train ing, in unilateral cases, the values of both upward and downward SPV r ecovered to the control range. In bilateral cases, the downward SPV va lues returned to the control range, whereas the values of upward SPV e xceeded the control range. The frequencies of both upward and downward OKN in controls were about 3.0 Hz. In unilateral and bilateral cases, before and after training, the OKN frequencies approximated 3.0 Hz, s howing no significant differences. The recovery of the SPV in unilater al and bilateral cases after training suggests that OK stimulation act s to stabilize the body and consequently to provoke pronounced OKN, du e to eye-head-body co-ordination. The asymmetry of SPV after training in bilateral cases might be a result of the lack of otolith function.