Functional acute acquired comitant esotropia: clinical characteristics and efficacy of single Botulinum toxin type A injection.

[BACKGROUND] To 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).

[METHODS] This 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.

[RESULTS] Twenty-two AACE cases were included. Compared with preinjection deviation, the postinjection deviation in the primary position was smaller for near (p < 0.001) and distance (p < 0.001) fixation at 3 months after injection (BTXA). Furthermore, convergence was better for near (p = 0.003) and distance (p < 0.001) fixation, divergence was better for near (p = 0.021) and distance (p < 0.001) fixation, accommodation was better in the right (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.

[CONCLUSIONS] AACE 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.