Cold Caloric-Induced Changes of Otolithic Eye Deviations in Rabbits

Tchae, Sayong; Park, So Young

Abstract

BACKGROUND AND OBJECTIVES: The otolith organs serve for gaze stabilization, posture control, and spatial orientation by sensing linear accelerations of head movements. But, the clinical vestibular testings are generally focused on the function of horizontal semicircular canal. Unilateral otolithic dysfunction cannot be identified and lateralized because a surviving intact otolith can support bidirectional responses. The aim of study was to test unilateral otolith function by applying caloric stimulation to unilateral labyrinth. MATERIALS AND METHOD: We made a magnetic search coil system combined with tilt apparatus for a rabbit and measured three-dimensional eye movements. Responses were evoked by position change and cold caloric stimulation. Unilateral ear was irrigated with ice water in various static head positions, and the dynamic changes of the existing eye deviations were observed.
RESULTS
Static head tilts produced compensatory eye deviations. In the resting position, after cold caloric stimulation of each ear, the directions of eye deviations were in reverse of the vertical eye movement plane. In both lateral tilt positions, the eye deviations decreased after caloric stimulation of the lower ear, and increased after stimulation of the upper ear in the vertical plane. In the pitch down position, the eye deviations decreased after caloric stimulation of each ear in the torsional plane.
CONCLUSION
Cold caloric stimulation evoked regular dynamic changes of the otolithic eye deviations produced by static head positions. We propose that this method might be useful for lateralization and evaluation of the unilateral otolith dysfunction.