Efficacy of Botulinum Toxin in the Treatment of Convergence Spasm

Previous studies have shown that botulinum toxin can be an important adjunct to management of convergence spasm. However, we have not experienced the same level of success in our cohort of patients.

Using retrospective review, we collected data on patients presenting to our department with convergence spasm. This included presenting symptoms, examination findings, response to atropine and plus lenses, number and dosage of botulinum toxin injections received, and the status at last follow-up/discharge.

We identified a total of 6 patients with a male: female ratio of 1:1 and mean age of 44.3 years. Commonest symptom was diplopia followed by headache and blurred vision. Depression was present in 4 out of 6 patients. Average pre-injection deviation for near was 32.5 PD ET (Prism Diopters esotropia) and for distance was 27.7 PD ET. All of the patients received botulinum toxin injections to the medial rectus muscle. The response to toxin was variable with an average near deviation at 2 weeks of 10 PD XT (exotropia), range 20 PD XT to 25 PD ET and at 3 months 12.5 PD ET (10 PD XT to 35 PD ET). At the last follow-up, after the toxin effect had worn off, all the patients returned to the pre-injection levels and the symptoms recurred.

The response of patients with convergence spasm to botulinum toxin was variable with a recurrence of the deviation once the effect wore off. In our experience, botulinum toxin has a limited role in the management of convergence spasm.