Botulinum toxin A injections show promise for treating convergence insufficiency

As the use of botulinum toxin A injections as a strabismus treatment has been well studied, investigators evaluated their effectiveness in patients with convergence insufficiency (CI).

Study design

This was a retrospective chart review of 23 patients who received lateral rectus botulinum toxin A injection(s) for CI at an academic eye center in Denmark between 2013 and 2018. Included patients had previously been treated with convergence exercises, base-in prism reading glasses, or surgery; patients aged ≤18 years and those previously treated with botulinum toxin were excluded.

Outcomes

Exophoria at near decreased by a median deviation of 8 PD at the initial 1-month follow-up visit and remained at 4 PD below baseline at the final 6-month visit. The near point of convergence was unchanged and the AC/A ratio was increased at both follow-up visits. At the 6-month follow-up visit, 23% of patients reported improved reading symptoms.

Limitations

The study was retrospective and did not use a standardized questionnaire to evaluate change in symptoms. Change (increase) in fusional vergence, a possible mechanism of action to explain the durable treatment effect in some patients, was not measured before or after treatment.

Clinical significance

Patients with symptomatic CI who have tried convergence exercises and base-in prism reading glasses do not currently have a reliably successful surgical treatment. Therefore, if botulinum toxin injections can help even a minority of patients, they are a welcome additional treatment option. A prospective study with a standardized symptom questionnaire and a control group is important to establish botulinum toxin as a standard treatment option.