Binocular Inhibition May Not Be to Blame for Slower Reading in Amblyopia

Binocular inhibition likely does not play a role in slow binocular reading among children with amblyopia, according to a study published in Optometry and Vision Science. Instead, a fellow eye deficit resulting from binocular vision experience disruptions may be to blame, the report suggests. 

Researchers included children with unilateral amblyopia (n=38; mean age, 10.0 years; 55% girls) who were referred to the Retina Foundation of the Southwest between 2017 and 2022 and age-matched control group participants (n=36; mean age, 10.3 years; 39% girls) in the cross-sectional analysis. Participants underwent a vision evaluation that included crowded monocular best-corrected visual acuity, stereoacuity, and binocular and monocular silent reading assessments using eye-tracking goggles. The research team determined reading rates, the number of forward and regressive saccades, and fixation durations among the cohort.

Participants with amblyopia and control group individuals demonstrated similar comprehension, as determined by comprehension scores, during both binocular (94% vs 91%; P =.13) and fellow eye (94% vs 94%; P =.95) reading tests. The pediatric group with amblyopia showed slower reading speeds compared with the control group for both binocular and fellow eye conditions (P =.016 and P =.010, respectively), but individuals with amblyopia exhibited similar reading speed and saccadic behaviors under both conditions. Binocular vs fellow eye assessments among individuals with amblyopia yielded comparable reading speed (176 vs 173 words per minute; P =.69), number of forward saccades (104 saccades/100 words vs 97 saccades/ 100 words; P =.18), number of regressive saccades (21 saccades/100 words vs 22 saccades/100 words; P =.75), and fixation duration (0.31 vs 0.32 seconds; P =.44).   

Compared with control group participants, individuals with amblyopia had more forward saccades during binocular (t, 3.1; P =.003) and fellow eye (t, 3.2; P =.002) reading and more regressive saccades during fellow eye reading (t, 2.5; P =.016), but not during binocular reading (t, 1.4; P =.16).

“It is becoming increasingly clear that visual and ocular motor deficits can occur in the fellow eye of amblyopic individuals, and that other daily tasks involving vision, such as motion perception and fine motor ability, are often impaired when viewing with both eyes,” according to the researchers. “Fellow eye deficits compared to controls may be indicative of binocular dysfunction that arises from binocularly discordant visual experience early in life in amblyopic children.”

Study limitations include failure to consider the impact of socioeconomic status and parental education on reading speed or assess intelligence quotient among participants.