The correlation between change in near-dissociated phoria and vergence dynamics

Visual fatigue is defined as weariness or discomfort localized in either the head or the eye after a visually demanding task. The etiology of visual fatigue is insufficiently understood in vision research. This study investigates the correlation between changes of near-dissociated phoria versus vergence dynamics defined as the ratio of convergence average peak velocity to divergence average peak velocity. Four degree convergence and divergence eye movements as well as phoria levels were recorded using an infrared eye movement monitor from five subjects. Preliminary data show a high correlation between the changes in phoria versus the change in vergence dynamics. Results suggest that the amount of changes in the two parameters, phoria and vergence dynamics, are one of many factors which may infer why some people are more prone to visual fatigue than others.