Dichoptic Attentive Motion Tracking is Biased Toward the Nonamblyopic Eye in Strabismic Amblyopia

Purpose: To determine whether attention is biased toward the nonamblyopic eye under binocular viewing conditions in adults with anisometropic or strabismic amblyopia. We first determined whether attention could be allocated preferentially to one eye in visually normal observers performing a dichoptic attentive motion tracking task. We then assessed dichoptic attentive motion tracking in amblyopia. Methods: Participants performed a multiple-object tracking task under the following three viewing conditions: target dots to the dominant eye and distractor dots to the nondominant eye (DE condition), vice versa (NDE condition), or all dots to both eyes (binocular condition). Interocular attentional asymmetry scores were computed as the difference in accuracy between DE and NDE conditions. An interocular contrast difference favoring the amblyopic eye was used for all conditions to neutralize amblyopic eye suppression. To test for confounding effects of suppression, participants completed a separate dot enumeration task under dichoptic presentation conditions to obtain an interocular enumeration asymmetry score. Results: Participants with normal vision demonstrated similar accuracy between the DE and NDE conditions and exhibited slightly impaired performance under dichoptic compared with binocular viewing conditions. Participants with strabismic/mixed amblyopia had significantly higher interocular attentional asymmetry than participants with normal vision or with anisometropic amblyopia, whereby attention was biased toward the nonamblyopic eye. The latter two groups did not exhibit a bias in interocular attention. No interocular asymmetries for the enumeration task were observed for any group. Conclusions: A nonamblyopic eye bias in the interocular allocation of attention may contribute to the binocular vision impairments caused by strabismic amblyopia.