Long-term efficacy of botulinum toxin for treatment of acquired non-accommodative comitant esotropia

Abstract

Acquired non-accommodative comitant esotropia (ANAET) represents a distinct subclass of esotropia that predominantly manifests in older children and adults. Injection of Botulinum Toxin A (BTX) to the extraocular muscle has been used to treat strabismus and a variety of other ocular conditions. In this study, we aimed to evaluate the long-term effectiveness of BTX injections for treating ANAET. In the Department of Ophthalmology at Seoul National University Bundang Hospital between the years 2010 to 2022, a total of 42 patients diagnosed as ANAET with a distant angle of esodeviation ≤ 25 PD and treated with BTX injection were retrospectively reviewed. Data collected from the patients' records included the angle of distant and near esodeviation before injection, post-treatment ocular alignment at distance and near at 2 weeks, 3 months, 6 months, 1 year, and the last follow-up examination, the number of injections and dosage of BTX, and complications after treatment. Treatment was considered successful if the final ocular alignment showed esophoria of 6 PD or less during distant fixation. The baseline esodeviation, determined by the maximum angle of esodeviation at distance before the first BTX injection, was 14.5 ± 5.6 PD. The mean duration from the last BTX injection to the final outpatient visit was 23.7 ± 16.1 months. The treatment success rates for all patients were 90.5% (38/42) at 6 months, 76.2% (32/42) at 1 year, and 73.8% (31/42) at the final examination. By multivariate analysis, the baseline angle of esodeviation (p = 0.008) was the only significant factor related to final success. BTX injection can be a highly favorable therapeutic option for ANAET patients. Specifically, if the maximum angle of deviation in ANAET patients is 15PD or less before treatment, it is advisable to attempt BTX therapy as a first-line treatment option for long-term success.

Keywords: Acquired Non-accommodative Comitant Esotropia; Acute Acquired Comitant Esotropia; Botulinum Toxin; Esotropia; Strabismus treatment.

Fig. 1

Change in the maximum angle of esodeviation after the last injection of botulinum toxin A into both medial rectus muscles. After the last injection, the maximum angles of esodeviation at distance had significantly improved at 2 weeks, 3 months, 6 months, 1 year, and at the final visit. A positive number represents esodeviation and negative number stands for exodeviation. PD prism diopters, yr years, mo months, wk weeks. *P value < 0.05 by Wilcoxon signed-rank test compared with the angle of esodeviation before BTX injection.

Fig. 2

Kaplan-Meier survival curves after the last injection of botulinum toxin A into both medial rectus muscles. The group with a smaller baseline esodeviation (≤ 15 PD) showed a higher success rate compared to the group with a larger baseline esodeviation (> 15 PD) (p = 0.026 by log rank test). The estimated mean time to failure was 50.8 ± 4.2 months in the smaller baseline esodeviation group (≤ 15 PD), and 34.7 ± 6.8 months in the larger baseline esodeviation group (> 15 PD). Data were censored at the time of last follow-up examination.