fixation revealed mostly rightward directed square-wave jerks. They had a mean amplitude of 0.5 degrees, a mean inter-saccadic interval of 185 msec, and a variable frequency ranging from 0.5 to 2 Hz with intermittent 3 to 4 Hz bursts. These square-wave jerks became more prevalent as testing continued. Saccadic tracking (io deg amplitude, 5 deg left and right of midline; temporal randomization) revealed highly variable metrics, at times exhibiting: (i) large (0.5 to 2 deg) dynamic overshoots on rightward gaze; (2) large (0.5 to 2 deg) glissadic overshoots on both rightward and leftward gaze, sometimes following a rightward directed static overshoot; (3) hypometric saccades to the right and left requiring a subsequent one- to two-degree corrective saccade (200 msec later) to attain accurate foveation; and (4) normometric saccades to the left and right.

Mean saccadic latencies were within normal limits (195 msec) for both leftward and rightward directed saccades. Square-wave jerks of 0.5 degree were intermittently present, at times occurring in couplets, during the intersaccadic fixation periods. Saccades had normal peak velocities in both directions. During constant velocity pursuit (io amplitude, 5 deg left and right of midline), the patient easily tracked targets ranging in frequency 0.2 to 2 Hz. Pursuit gain was normal (0.93 to the left and o.88 to the right). There was evidence of prediction to the right but not to the left, with a large initial one- to three-degree saccade embedded in each response in both directions. To the left this consisted of a square-wave jerk, whereas to the right it consisted of a single saccade. Versional movements were similar under both monocular and binocular viewing conditions. When asked to perform symmetrical (midline) vergence tracking of a pencil point moving slowly (i.e., ramp-like) between 57 and 17 cm, the patient easily followed the target in both the con vergent and divergent directions. However, numerous rightward directed square-wave jerks of 0.5 degree amplitude with a frequency of i Hz were always present.

Fig. 3. Representative objective eye movement recordings in our subject during binocular viewing. A. Fixation, B. Saccades, C. Pursuit, D. Vergence. In the position traces, upward deflections represented leftward movement and downward deflections represented nghtward movement. Time markers represent seconds.