Attention is biased towards the fellow eye in strabismic amblyopia

Abstract

Purpose : While covert spatial attention appears to be functionally intact in amblyopia, amblyopia is associated with impaired performance on visual attention tasks such as multiple object tracking (MOT). In this prospective observational study, we used a dichoptic MOT task to investigate whether amblyopia involves an attentional bias favoring the dominant (non-amblyopic) eye during binocular viewing.

Methods : Participants with normal vision (n=16), anisometropic amblyopia (n=6), strabismus and/or mixed amblyopia (n=5) performed a MOT task under 3 conditions: viewing 3 target dots with the dominant eye and 7 distractor dots with the non-dominant eye (DE condition), vice versa (NDE condition), or all dots with both eyes. Participants tracked the dots (1^o diameter, 10^o/s, 14^o x 14^o field, 5 sec presentation) while fixating a central cross. Following a partial report procedure, participants indicated whether a highlighted dot was a target dot at the end of each trial. Sensory eye dominance was determined using a dichoptic global motion procedure. An interocular contrast difference favoring the amblyopic eye was used for all conditions to overcome amblyopic eye suppression. To test for any confounding effects of suppression, participants completed a separate dot enumeration task under dichoptic presentation conditions.

Results : MOT performance was assessed by percent accuracy (mean ± SE) for the normal group (DE 83±3%; NDE 78±4%), anisometropia group (DE 85±4%; NDE 88±2%) and strabismus/mixed group (DE 89±2%; NDE 64±6%). An asymmetry score was computed by subtracting NDE from DE accuracy (normal -2±3%; anisometropia 5±3%; strabismus/mixed 25±7%). Asymmetry scores varied significantly across groups (H[2]=6.9, p=.03). Pairwise comparisons revealed a significant difference between the normal and strabismus/mixed groups (U=13, p=.025) and between the anisometropia and strabismus/mixed groups (U=3.5, p=.03). Normal and anisometropia groups did not significantly differ (U=64.5, p=.231). The groups did not differ in enumeration task performance (H[2]=1.3, p=.53).

Conclusions : Attention is biased in favor of the fellow eye in strabismic amblyopia. This bias may contribute to the binocular vision impairments caused by amblyopia.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.