Effect of eye movements on dynamic equilibrium.

The purpose of this study was to determine whether visual improvement of balance varies depending on the movement of the eye. Three movements were compared: static visual fixations, saccadic eye movements, and smooth pursuit eye movements. The subjects in this study were 35 healthy female volunteers. Balance was defined as the subjects' ability to maintain their equilibrium while keeping the unstable platform on which they stood within 5 degrees of the horizontal plane. The testing protocol consisted of five recorded practice trials, during which the subjects tried to maintain their balance without any visual instructions, and nine experimental trials, during which they tried to maintain their balance while visually following a videotaped target light projected onto a screen. The target light was sequenced randomly to remain stationary, move in a continuous horizontal path, or alternately jump between right and left. Data were analyzed using a one-way multivariate analysis of variance for repeated measures. A significant effect of vision on balance was found. The t tests for correlated samples revealed that time in balance during visual fixations and saccades was significantly longer than during tracking eye movements. We, therefore, concluded that tracking eye movements have a negative effect on balance. This information can be useful in treating patients with balance problems. For example, instructing patients to fixate visually on an object may aid their stability. Visual tracking of a moving limb, however, may impair a patient's stability.