Erratic eye tracking in schizophrenic patients as revealed by high-resolution techniques

Using high-resolution infrared oculography with digital recording and analysis techniques, we tested several types of eye movements in 19 schizophrenic patients and 11 normal controls. Abnormal slow pursuit eye movements, seen in about half of the patients, were characterized by erratic inaccuracies in position, velocity, and phase. Tracking errors were quantitatively assessed by their root mean square (RMS) error. Position RMS errors fell into two clearly separated groups, with 10 of 19 patients clustering about the normal controls and the remaining 9 having much higher errors than normal. Although several of these poor trackers had an excess of saccades or low pursuit gain, these abnormalities were not primarily responsible for the large erratic tracking errors. Saccades in response to unpredictable target jumps had normal latencies (reaction times) and velocities, but were more hypometric and variable in accuracy than those of controls. These saccadic abnormalities did not correlate with the patients' position RMS errors during slow pursuit.