Motion of the eye immediately after a saccade

Dynamic overshoot is a small saccade that follows a main saccade, in the opposite direction, with no delay. To re-examine prior reports of dynamic overshoot, the properties of dynamic over-shoot were studied in six normal subjects. The post-saccadic drift of eye movements was studied as well. Horizontal eye movements were recorded with the magnetic-field/search-coil method. System noise level was 0.05 deg. Dynamic overshoot occurred with a frequency of about 13% and was more frequent for saccades 10 deg or less. Its mean size was 0.15 deg and its peak velocity showed it to be saccadic in nature. Binocular recordings for three subjects showed that when dynamic overshoot occurred it was almost always in the abducting eye which also had the least post-saccadic drift. The abducting eye seldom had dynamic overshoot and consistently had a more pronounced post-saccadic drift, almost always in the onward direction. We suggest that, at the end of a saccade, the eye normally is brought to rest by a braking pulse and dynamic overshoot occurs when the braking pulse is accidentally too large. It would appear to serve no useful purpose. Why dynamic overshoot is monocular and coincides with the eye having less post-saccadic drift is unclear.