[Long term outcomes of botulinum toxin injections in infantile esotropia].

Purpose: To evaluate long terms outcomes of botulinum toxin in infantile esotropia by measuring the amount of microtropia 24 months after injection. Secondary purpose was to identify predictive factors of microtropia.
Methods: A retrospective, single-center study was performed at the university medical center in Bordeaux between 2001 and 2018, including all patients with infantile esotropia greater than 20 D. All patients received 5 or 7,5 IU of botulinum toxin A in each medial rectus, once or twice depending on the angle of deviation after the first injection and after wearing full optical correction at least two months. We noted the angle at 1, 6, 12 and 24 months, the occurrence of any complications and the need for later strabismus surgery. The primary endpoint was the achievement of a microtropia less than 8 diopters (D) at 24 months post-injection. We evaluated the predictive factors for microtropia with a Fischer's test.
Results: We included 30 patients with esotropia greater than 20 D. The mean follow-up after injection was 48 months ±30. The mean age was 16.24 months (7-29 months) with a female predominance in the population (SR=0.43). The mean pre-injection deviation was 41.25±12.17 D. The majority of patients were mildly (40%) or moderately (40%) hyperopic. At 24 months, 46.7% microtropias were obtained (95% CI: 28.9%-64.5%). The change in mean angle at 1, 6, 12 and 24 months post-injection was -8.57±25.21 D; 14.48±13.40 D; 18.38±12.07 D and 21.23±14.97 D, respectively. No factors were predictive of microtropia. Of the 30 children, 3 had transient ptosis requiring strips and 12 showed an exotropia at 1 month. All complications were self-limited and without consequences. 3 children had a second injection of botulinum toxin, which in 2/3 of the cases resulted in a long-lasting microtropia. 26.7% (n=8) of the children underwent secondary surgery. Obtaining a microtropia 24 months after injection statistically significantly reduced the need for secondary strabismus surgery: 92.9% P=0.039% CI 95% (0.002; 1.0606).
Conclusion: Botulinum toxin appears to be a less invasive and more conservative alternative to surgery in children with infantile esotropia. In 46.7% of cases, microtropia is achieved. An improvement was noted in 90% (n=27) of the children with a reduction of half (21.23 D) of the mean post-injection angle at 24 months. When effective, it significantly reduces the need for secondary surgery.
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