Visual suppression test.

Visual suppression of caloric nystagmus was studied in normal adults and in 98 clinical cases in order to justify the application of the procedure as a clinical test. The maximum slow phase velocity during ten seconds in darkness and the slow phase velocity during ten seconds in light were taken from the recordings and measured. The mean values of these slow phase velocities were calculated and the mean slow phase velocity in darkness was assigned a value of 100%. The value which the slow phase velocity in light subtracts from the slow phase velocity in darkness, represents the visual suppression. It was determined that visual suppression of the slow phase velocity of caloric nystagmus was 48 +/- 10% in 22 normal adults. This was caused by the visual fixation mechanisms. Cases in which lesions were diagnosed in the cerebellum, such as spinocerebellar degeneration and cerebelitis, showed reduced or abolished visual suppression. The lesion side can be determined by this test. Compensation following unilateral sudden loss of inner ear function can be measured by the visual suppression test.