Elements of the VOR

The vestibulo-ocular reflex (VOR) serves vision by generating conjugate smooth eye movements that are equal In velocity and opposite in direction to head movements, As a result, the eyes remain stationary with respect to the world, and Images of the world are stable on the retina. Visual acuity depends on the accuracy of vestibular smooth eye movements. As the eyes and head move in opposite directions, the ratio of eye velocity to head velocity, the VOR gain, must approximate unity. The phase of the VOR must be such that the eyes are 180 degrees out of phase with the head. By convention, this phase difference is called 0, Slippage of images on the retina over two to three degrees per second blurs visual acuity. If the gain of the reflexes too much above or below its ideal value of 1,0, a retinal image remains off the fovea although it may be transiently stable on the retina. If there is a phase lead of the eyes before the head or a phase lag of the eyes behind the head, the target image is never stationary on t retina. Saccades or nystagmus quick phases opposite to vestibular smooth eye movements are dispatched to bring the fovea toward a new target when the VOR takes them away from it.