Changes in the time constants of the vestibulo-ocular reflex and optokinetic afternystagmus following unilateral ablative vestibular surgery.

Changes in the time constants and gains of the vestibulo-ocular and optokinetic systems were studied in seven patients. Angular acceleration pulse and optokinetic stimuli were administered to three normal subjects and also to seven patients at specific intervals after unilateral ablative vestibular surgery. The gains and the time constants of the two systems were compared. Regression analysis showed that the vestibulo-ocular and optokinetic time constants for slow phase eye movements away from the ablated ear declined significantly after surgery in the patient group, but that the gains did not. A theory based upon variability of system parameters by the CNS is outlined to explain the changes in the dynamics of the two systems after surgery. The data from this study suggest that the time constant may be a useful parameter in clinical vestibular testing.