Visual fixation of caloric nystagmus with special reference to a new index

The effects of visual fixation upon caloric nystagmus were computed in each parameter as a measure. The percentage reduction established with slow-phase velocity best distinguished normal from abnormal visual fixation at the line of 60%. However, if a +/- 5% safety margin is taken into account, 11 of 176 ears showed false-negatives. The number of nystagmus beats in normals decreased markedly during the period of fixation. In abnormals, the number of nystagmus beats increased definitely during the fixation period. Based on this fact, the product of slow-phase velocity multiplied by the number of nystagmus beats was assessed as the fixation-suppression index. As a result, 11 ears showing false-negative slow-phase velocity decreased to 2 ears. Thus, this modified fixation-suppression index seems to be an appropriate parameter to separate normal from abnormal fixation-suppression of caloric nystagmus.