BackgroundTo examine the clinical features of acute acquired comitant esotropia (AACE) and to evaluate the clinical effectiveness of a single injection of botulinum toxin type A (BTXA) on binocular visual function (BVF).MethodsThis retrospective, observational case series study enrolled patients with AACE examined from October 2018–May 2019. BTXA was injected into the both medial rectus muscles. The refractive error, best-corrected visual acuity (BCVA), stereoacuity, vergence, accommodation, the horizontal angle of deviation, and the gradient accommodative convergence/accommodation (AC/A) ratio were measured pre- and post-BTXA injection. Data pre- and postinjection were compared by the Wilcoxon signed-rank test. A Spearman correlation coefficient was calculated to explore the relationships between demographic characteristics and BVF.ResultsTwenty-two AACE cases were included. Compared with preinjection deviation, the postinjection deviation in the primary position was smaller for near (p p p = 0.003) and distance (p p = 0.021) and distance (p p = 0.011) and left (p = 0.004) eyes, and the gradient AC/A ratio was better at the third month after injection (p = 0.001). Stereoacuity was improved in 11 (50%), unchanged in 5 (22.73%) and decreased in 6 (27.27%) patients. The preinjection stereoacuity (p = 0.013,r = 0.522) and preinjection deviation for near (p = 0.015 r, = − 0.512) and distance (p = 0.009,r = − 0.541) were significantly associated with patient age.ConclusionsAACE is characterized by a high AC/A ratio and low accommodation. A single injection of BTXA is effective for AACE. Deviation, stereoacuity, and the therapeutic effect of BTXA may be correlated with patient age.