Effect of eccentric gaze on pursuit.

The effect of eccentric gaze on pursuit eye movements was studied with electro-oculography in normal human subjects and a patient with defective pursuit. Sinusoidal target trajectories were centered about the primary position of gaze and eccentric, horizontal positions of gaze. Eccentric gaze decreased pursuit gain (eye velocity/target velocity) when the eyes moved farther eccentrically in the orbits and increased pursuit gain when the eyes moved toward the centers of the orbits. The magnitude of these effects increased with increasing eccentricity of gaze, increasing peak target velocity, and decreasing pursuit gain during tracking of target trajectories centered about the primary position. These effects can be caused by the elastic forces of the extraocular muscles, globe and other orbital tissues. The pursuit subsystem cannot compensate for these factors at high target velocities, or when it is impaired by pathologic lesions.