Abstract

Optimal visual function requires that images of interest be maintained on the fovea with sufficient stability, despite unintended but ubiquitous rotations and translations of the head. This gaze stabilization is necessary since retinal image velocities exceeding 2-3°/sec are associated with a log-linear decline in visual acuity(2). We show elsewhere in this volume that, during normal vision, gaze stability is achieved by a combination of angular and linear vestibulo-ocular reflex responses, as well as coordination of coupling between head rotation and translation. The head effectively moves in a broad arc about an axis of rotation anterior to the head. Gaze stabilization during natural activities such as standing and ambulation is most effective during viewing of remote targets, but is degraded with target proximity. Gaze stabilization must also be achieved when subjects wear head-mounted devices such as video or telescopic spectacle magnifiers. Such devices enlarge images on the retina and markedly alter the demands placed on gaze stabilization reflexes. Due to technical limitations, prior studies of the effects of telescopic spectacles emphasized visual enhancement of the gain (compensatory eye velocity divided by head velocity) of the angular vestibulo-ocular reflex (VOR). These studies reported the seemingly paradoxical observation that while large and appropriate enhancements of VOR gain occurred when subjects wearing telescopic spectacles made repetitive, predictable movements(3), gain enhancements were considerably smaller during unpredictable head movements or those incidental to natural activities(4). We investigated this problem by directly measuring gaze stability in all degrees of rotational and translational freedom in naturally-moving subjects wearing telescopic spectacles.

© 1997 Optical Society of America