Effects of strabismic amblyopia on visuomotor behavior: part II. Visually guided reaching

To examine the effects of impaired spatiotemporal vision on reaching movements in participants with strabismic amblyopia and to compare their performance to those with strabismus only without amblyopia and to visually normal participants.

Sixteen adults with strabismic amblyopia, 14 adults with strabismus only, and 16 visually normal adults were recruited. Participants executed reach-to-touch movements toward targets presented randomly 5° or 10° to the left or right of central fixation in three viewing conditions: both eyes, monocular amblyopic eye (nondominant eye for participants without amblyopia), and monocular fellow eye (dominant eye for participants without amblyopia). Visual feedback of the target was removed on 50% of the trials at the initiation of reaching.

Both groups with abnormal binocular vision (strabismic amblyopia and strabismus only) had reach latency, accuracy, and precision comparable to visually normal participants when viewing with both eyes and fellow (dominant) eye. Latencies were significantly delayed by more than 30 ms in all participants with reduced binocularity during amblyopic eye or nondominant eye viewing compared with controls (P < 0.0001). Participants with strabismic amblyopia and negative stereopsis also had reduced reach precision (i.e., increased variability) during amblyopic eye viewing. In contrast, participants with strabismus only and negative stereopsis had comparable precision across all viewing conditions. Participants with strabismus only and those with strabismic amblyopia used a similar motor strategy; regardless of viewing condition, reach peak acceleration was significantly reduced (P < 0.05) and the duration of acceleration phase was extended in comparison with visually normal participants. There were no significant differences for the deceleration phase.

Participants with strabismic amblyopia and those with strabismus only attain relatively normal reach accuracy and precision. However, they use a different reach strategy that involves changing the motor plan. A similar compensatory strategy was reported previously in participants with anisometropic amblyopia. Our results provide further support that normal binocular vision during development provides important input for the development of visually guided reaching movements.