Visual-vestibular interaction with vergence

Abstract

Introduction. Vergence, or fixation distance, influences the vestibulo-ocular reflex (VOR). The VOR-gain increases with decreasing fixation distance. This distance is primarily resolved visually. Is visual control maintained at high frequency head movements? We investigated whether the visual system, during high frequency headshaking and a quick change of gaze direction, controls the eye movements in such a way that binocular vision is maintained. Material and methods. Two-dimensional eye movements were recorded with the scleral coil technique during active head rotation (0.5–4 Hz) while fixating an object. The subject was wearing glasses containing two displacement prisms (OD = 4D, OS = 1D). During headshaking, the head was tilted whilst the subject looked through the prisms at the fixation object. Results. Within 1.5 s after head tilt, the correct amount of vergence change was reached. For high shake frequencies this occurred within 0.5 s. The vergence amplitudes before and after tilt were comparable. Conclusion. It appears that the eyes can compensate for head movements independent of gaze direction even at high shake frequencies. The VOR controls the high frequency eye movements and the visual system updates at a lower frequency mainly when the head velocity is almost zero.