Smooth Pursuit: Some Clinical Considerations

Smooth pursuit serves to maintain foveation of slowly moving targets. When pursuit velocity fails to match target velocity, a series of catch-up saccades compensate for the limited smooth pursuit. The smooth pursuit system is measured by its gain, the ratio of its output, eye velocity, to its input, target velocity. Smooth pursuit is limited by the acceleration of the eyes, rather than by- their frequency or their velocity alone. Humans can attain eye accelerations of about 1.200 deg/sec at velocities of 150 deg/sec but when tracking to and fro targets, mean velocities attain about 40 deg/sec. During clinical examination pursuit becomes saccadic at target speeds over 40 deg/sec; this appears to reflect acceleration saturation. since normal subjects can achieve smooth pursuit velocities of 90 deg/sec when tracking large amplitude ramp velocities of 100 deg/sec.