Botulinum Toxin Injections May Reduce Degree of Strabismus

Botulinum toxin injections may help manage strabismus, or at least reduce the angle so that surgery may be planned for a smaller deviation, according to a study published in the Canadian Journal of Ophthalmology. 

The study included 86 participants who had received botulinum toxin injections. Mean age of patients was 10.8±16.3 years (range, 4 months to 65 years). A total of 44 patients were men and boys (51.2%) and 42 were women and girls (48.8%). All patients were assigned a subgroup depending on their diagnosis; 29 patients had infantile esotropia (ET), 9 had partially accommodative ET, 13 had residual ET, 4 had 3rd cranial nerve paralysis, 15 had 6th cranial nerve paralysis, 4 had Duane retraction syndrome, and 13 had nonaccommodative ET.

All participants received an injection consisting of 100 units of botulinum toxin diluted with 0.9% NaCl solution to the targeted muscle without conjunctival incision or electromyelography guidance. They followed up at 2 weeks, 1 month, 3 months, and 6 months, when they were examined for primary position, duction deficits, ptosis, and overcorrection caused by the toxin.

The primary outcome measure was success rates of treatment for different types of strabismus, and success was defined as a final horizontal deviation of 10 prism diopters or less. Success rates were 31% for infantile ET, 25% for partially accommodative ET, 61.5% for residual ET, 25% for 3rd cranial nerve paralysis, 13.3% for 6th cranial nerve paralysis, 75% for Duane retraction syndrome, and 38.5% for non accommodative ET.  Improvement in deviation size after botulinum toxin treatment was significant in patients with infantile esotropia (P =.001), residual esotropia (P =.001), and non accommodative esotropia (P =.03). Success rate was not correlated with age (r=0.040, P =.8), sex (r=0.083, P =.6), mean dose (r=0.149, P =.35), or total dose (r=0.165, P =.29), but was significantly correlated with deviation size (b=0.077, P =.0001).

“Generally, we prefer botulinum toxin injection as a first choice in patients with neurologic disorders because surgery in such patients is reported to be less successful,” according to investigators. “We did not find the difference in success rate in infantile ET with and without neurologic defects.”

Study limitations include a relatively small sample size and retrospective nature.

Reference

Niyaz L, Yeter V, Beldagli C. Success rates of botulinum toxin in different types of strabismus and dose effect. Can J Ophthalmol. Published online January 14, 2022. doi:10.1016/j.jcjo.2021.12.002