Effect of a parafoveal microlesion made with an argon laser on smooth-pursuit eye movements of monkeys.

The significance of the parafoveal region in processing information about target velocity to initiate ocular pursuit was evaluated by making a small paracentral scotoma in monkeys trained to pursue a slowly moving target. In the experimental paradigms in which the image had to cross the scotoma, the small retinal lesion (greater than 2 degrees) gave a direct effect upon the ability of monkeys to pursue the target motion. The abnormal pursuit was characterized by a marked reduction of eye velocity. Evaluated from the initial portion of the pursuit immediately following the first corrective saccade, the eye velocity was as low as 50 to 60% of the target velocity. The abnormality was more pronounced in slow pursuit (15 to 20 degrees/s) than in fast pursuit (25 degrees/s). The data indicated that the small retinal region at the boundary of the macula plays an important role in sampling target velocity during the initial part of smooth-pursuit eye movement.