Botox Effective for Convergence Insufficiency

Continued Improvement Requires Maintenance Doses

Ron Zimmerman

April 06, 2012

April 6, 2012 (San Antonio, Texas) — A new study conducted by researchers at Moorfields Eye Hospital in London, United Kingdom, found good results in a small sample that used botulinum toxin injections in the lateral rectus muscle for convergence insufficiency.

Results were presented here at the American Society of Pediatric Ophthalmology and Strabismus (AAPOS) 38th Annual Meeting.

Convergence insufficiency is a neuromuscular anomaly in which the patient cannot converge on near-centered tasks with exotropia at distance. Despite available surgical treatments, some patients remain symptomatic.

The retrospective analysis identified 10 patients (8 women and 2 men) ages 9 to 62 years (mean age, 32 years) treated with injections between 1982 and 2010. "Convergence ranged from 18 cm to complete paralysis in 3 patients," Emma L. Dawson, DBO, from Moorfields Eye Hospital, London, and colleagues wrote in their abstract. "Previous management included convergence exercises in all patients, prisms in 7 (70%) and surgery in 4 (40%)."

Emma L. Dawson

After botulinum toxin injections into a single lateral rectus muscle, 8 patients (80%) had improvement 2 to 3 weeks later. One patient declined further botulinum toxin injections. The symptoms returned within 3 months to 6 years in the remaining 9 patients. The number of maintenance injections (which 7 patients received while 2 went on to surgery) ranged from 2 to 11, with a mean of 4. Mean follow-up was 3.8 years.

"This is a very difficult group of patients to treat," explained Dawson in an interview with Medscape Medical News. "Once you've tried exercises and prisms and occlusion, this is one thing still to be tried."

Dawson found that in the small group of patients studied, a majority obtained significant improvements. "Some patients didn't need any more toxin, but others continued to [receive] maintenance toxin," she said. "What we tended to find was that each time they came back for treatment, the angle of squint was actually less and the gap between the injections actually increased. So, in this small group, it was a very useful treatment, as these are very unhappy patients."

Although this treatment is well-established for strabismus, Ms. Dawson believes that this is the first study to show results from the use of botulinum toxin for convergence paralysis.

When asked whether there were downsides, Ms. Dawson replied, "Not at all. You might get [a] slightly drooped eyelid, but that's very rare and that will recover. There are no other side effects and [the clinician is] not limited to the numbers of times you can inject a patient either."

Selim Koseoglu, MD, from Children's Hospital, Oakland, California, who was not part of the study, uses botulinum toxin for other ocular misalignment problems in his practice but has not yet used it for convergence insufficiency. "The bottom line is, I think, it is interesting in otherwise hopeless cases where you can't do anything else," he told Medscape Medical News.

"My concern was to see how long it lasts since Botox lasts, as you know, only 2 or 3 months. It appears they had some good success, but it still seems that it's just a transient improvement."

When asked whether the maintenance dosages are bothersome, Dr. Koseoglu replied, "The problem is the overcorrection, the double vision. Certainly, with these patients, you can't do anything else, but you can offer them injections for a few months and then they can be re-injected. Then, there [are] all these problems with the paralysis you're going to cause."

"Maybe it [didn't] happen to Dawson, but you get ptosis. You hit other muscles 30% of the time. But again, if there is no other treatment and the people are willing to undergo the procedure under local [anesthesia], then certainly you can do it."

Ms. Dawson and Dr. Koseoglu have disclosed no relevant financial relationships.

American Society of Pediatric Ophthalmology and Strabismus (AAPOS) 38th Annual Meeting. Poster #4. Presented March 25, 2012.