3D Eye Movement Analysis During Sinusoidal Off Vertical Axis Rotation in Human Subjects

Abstract

Objective—It has been reported that the eye movements induced by off vertical axis rotation (OVAR) are composed of two components: a bias component (BIC) and a modulation component (MOC). It was suggested that the MOC compensates for changes in head orientation with respect to gravity and that the BIC is related to the velocity storage mechanism. However, the characteristics of the otolith organs remain obscure. In order to investigate these characteristics, we performed a 3D analysis of eye movements induced by human sinusoidal s-OVAR, and compared the result with that of eye movements induced by constant c-OVAR.Material and Methods—Fifteen healthy human subjects participated in this study. OVAR stimulation was produced by rotation following tilt. After a 30° tilt, the subject was rotated sinusoidally at 0.05 and 0.02 Hz at 50°/s peak velocity. Eye movements were recorded using an infrared charge-coupled device camera, and the updated version of our standard computerized image recognition method was used to analyze them three-dimensionally.Results—The eye movements induced by s-OVAR consisted of two kinds of sine waves: low- and high-frequency components. The low-frequency component was related to the change in angular acceleration, and the eye movements were found to derive from the semicircular canals. In contrast, the high-frequency component was related to the change in head position, and the eye movements were found to derive from the otolith organs.Conclusion—s-OVAR may prove to be a useful tool for simultaneously assessing the functions of both the otolith organs and the semicircular canals.