Physics

Visual acuity

Refractive error

Ophthalmology

Optics

Surgery

Stereoscopic acuity

Strabismus

Botulinum toxin

Exotropia

Heterophoria

Esotropia

Anisometropia

Medicine

Vergence (optics)

BMC Ophthalmology

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 &lt; 0.001) and distance ( p &lt; 0.001) fixation at 3 months after injection (BTXA). Furthermore, convergence was better for near ( p = 0.003) and distance ( p &lt; 0.001) fixation, divergence was better for near ( p = 0.021) and distance ( p &lt; 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.

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