Effects of anisometropic amblyopia on visuomotor behavior, III: Temporal eye-hand coordination during reaching.

PURPOSE To examine the effects of anisometropic amblyopia on the temporal pattern of eye-hand coordination during visually-guided reaching. METHODS Eighteen patients with anisometropic amblyopia and 18 control subjects were recruited. Participants executed reach-to-touch movements toward visual targets under three viewing conditions: binocular, monocular amblyopic eye, and monocular fellow eye viewing. Temporal coordination between eye and hand movements was examined during reach planning (interval between the initiation of saccade and reaching) and reach execution (interval between the initiation of saccade and reach peak velocity). The frequency and dynamics of secondary saccades were also examined. RESULTS Patients with severe amblyopia spent a longer time planning the reaching response after fixating the target in comparison with control subjects and patients with mild amblyopia (P = 0.029). In comparison with control subjects, all patients extended the acceleration phase of the reach after target fixation (P = 0.018). Secondary (reach-related) saccades were initiated during the acceleration phase of the reach and patients executed these saccades with greater frequency than control subjects (P < 0.0001). The amplitude and peak velocity of reach-related saccades were higher when patients viewed with the amblyopic eye in comparison with the other viewing conditions (P < 0.001). CONCLUSIONS This is the first study to show that patients with anisometropic amblyopia modified the temporal dynamics of eye-hand coordination during visually-guided reaching. They extended the planning and execution intervals after target fixation and increased the frequency of secondary, reach-related saccades. These may represent visuomotor strategies to compensate for the spatiotemporal visual deficits to achieve good reaching accuracy and precision.