Bone conducted vibration to the mastoid produces horizontal, vertical and torsional eye movements.

INTRODUCTION: We have previously shown that bone-conducted vibration to each mastoid in humans results in small stimulus-locked horizontal and vertical eye movements suggesting that the ipsilateral superior oblique and the contralateral inferior rectus are activated. However, as torsional responses were not measured we have repeated the study by measuring torsional as well as horizontal and vertical responses in seven adult subjects during different directions of gaze.
METHODS: We measured stimulus-locked horizontal (H), vertical (V) and torsional (T) eye movements during brief stimulation to the mastoid unilaterally and bilaterally using a high-speed, high-resolution video technique. Bone-conducted vibrations were delivered to each mastoid separately as well as bilaterally using a Radioear B71 bone oscillator while the subjects viewed targets 2 metres away situated straight ahead and 10° to the right and left.
RESULTS: For unilateral stimulation the eyes moved downwards when directed away from the stimulated mastoid, along with bilateral counter-rolling away from the side of stimulation. Horizontal movements were small, with little effect of gaze position. Bilateral stimulation enhanced the downward responses.
CONCLUSIONS: Bone conducted vibration to the mastoid in humans produces vertical and torsional eye movements consistent with activation of the ipsilateral superior oblique muscle, and the contralateral inferior oblique muscle to produce counter rolling of the eyes away from the stimulated mastoid.