Abstract

Background and Objectives: It has been reported that vibration applied either on the mastoid or on the sternocleidomastoid (SCM) muscles induces nystagmus in normal subjects. The aims of the study were to characterize the direction and velocity of slow-phase eye movement which is induced by vibration in normal subjects and to propose the mechanism of vibration-induced nystagmus (VIN) in normal subjects. Materials and Method: We recorded eye movements during unilateral 100-Hz vibration on the mastoid bone and SCM muscles in 56 normal subjects. The subjects were divided into 4 groups in ages (20s, 30s, 40s, 50~60s). The directions of VIN, the degree of maximal slow-phase eye velocities were analyzed according to age. Positive value means slow-phase velocity (SPV) to the right side. Results: In 20s, vibration on right/left mastoids induced SPV of 1.2±2.0°/sec, 0±2.1°/sec and on right/left SCM muscles, 1.1±1.9°/sec, -1.2±2.5°/sec. In 30s, vibration on right/left mastoids induced SPV of 3.3±3.8°/sec, -0.3± 1.4°/sec and on right/left SCM muscles, 2.8±4.2°/sec, -1.0±1.5°/sec. In 40s, vibration on right/left mastoids induced SPV of 0±1.7°/sec, -0.2±1.2°/sec and on right/left SCM muscles, 0±1.8°/sec, 0±1.0°/sec. In 50~60s, vibration on the right/left mastoids induced SPV of -1.3±1.3°/sec, 1.2±1.3°/sec and on right/left SCM muscles, -0.6±0.9°/sec, 0.9 ±1.5°/sec. The directional preponderance of the slow-phase eye movement to the vibrated side was statistically significant in 20s and 30s, however, the preponderance of the slow-phase eye movement changed into the non-vibrated side in 50~60s. Conclusion: The proprioceptive input, changing major rotator from the inferior oblique muscle to the sternocleidomastoid muscles might explain the change of the directional preponderance of the slow-phase eye movements in normal subjects according to ages. Although this directional preponderance is not consistent in all age groups, it is still important in discriminating normal responses from abnormal responses which can be induced by vibration.

• Keywords: Vibration induced nystagmus;Age;Proprioceptive;Vestibule;