WHAT IS THE MINIMAL VESTIBULAR FUNCTION REQUIRED FOR COMPENSATION

Living with an uncompensated, abnormal vestibular system requires oppr essive modification of life style and often prevents return to work an d activities of daily living. Patients with vestibular abnormalities w ere studied to determine the minimal residual vestibular function requ ired to achieve compensation. Three groups of patients with (a) comple te unilateral loss of vestibular function with normal horizontal canal -vestibulo-ocular (HCVOR) function in the opposite ear, (b) complete u nilateral loss with abnormal HCVOR function in the opposite ear, and ( c) bilateral reduction of vestibular function from aminoglycoside toxi city underwent vestibuloocular (VOR), optokinetic (OKN), visual-VOR (V VOR), and computerized dynamic posturography (CDP) tests before and af ter therapeutic procedures. Results suggest that a minimal VOR respons e amplitude must be present for compensation of VVOR function to occur . The roles of VOR and OKN phase shifts in vestibular compensation are more complicated and require further study. Compensation of vestibulo spinal function does not necessarily accompany VOR or VVOR compensatio n. Ascending and descending vestibular compensatory mechanisms may inv olve different spatial sensory inputs. Results of these studies have i mportant implications for the diagnosis and treatment of patients with vestibular disorders, including selection and monitoring of patients for therapeutic regimens such as vestibular nerve section and streptom ycin therapy.