Treatment Option: Botulinum Toxin

Botulinum toxin (BT) for the management of strabismus was approved by the FDA in 1989 based on work by pediatric ophthalmologist Alan B. Scott, MD. BT can be the first-line treatment for certain forms of strabismus.

Indications

Acute comitant esotropia in children: BT can be injected to both medial rectus muscles early in the disease process. Treatment is noninferior to surgery, has lower cost and total anesthesia time, and is quicker to schedule than traditional incisional surgery.

Congenital esotropia: BT can have a high success rate as a primary mode for treatment of congenital esotropia less than 30 prism diopters. It can also be used to augment medial rectus recessions in very large-angle esotropia.

Strabismus associated with thyroid-associated orbitopathy: BT can be used early in the disease process, when the angle of strabismus is small and might not have stabilized.

Acute 6th nerve palsy: Even though the use of BT can be controversial in acute 6th nerve palsies, it can be considered in children to maintain binocularity as well as in adults
who are bothered by the double vision.

Cyclic esotropia: BT can eliminate the cyclic deviation in this rare form of strabismus. 

Variable strabismus in the setting of neurodevelopmental delays: Patients with neurodevelopmental delays may have variable angles of strabismus, making it difficult to devise a surgical dosage plan for incisional surgery. In such cases, BT can decrease the angle of strabismus over time, titrating the injections to the desired result.

Technique

The most commonly used preparation of BT for the management of strabismus is onabotulinumtoxin A (Botox®, Allergan). BT can be diluted to either 5 units/0.1ml or 5 units/0.05mland injected using a 27-gauge, 1.5-inch needle.

Adult patients: The injection can be performed with topical anesthesia. In the past, an electromyographicguided needle has been used, but it is cumbersome and not required to safely and accurately inject. After a topical anesthetic has been administered, a cotton-tipped applicator soaked with the anesthetic can be applied over the injection site while the patient is looking away from the muscle that is being treated. The injection is carried out transconjunctivally directly into the belly of the muscle.

Pediatric patients: General anesthesia is required to safely inject BT directly into the belly of the extraocular muscle transconjunctivally. This can be done either by holding the muscle with toothed forceps or by rotating the eye in the opposite direction of the muscle.

Outcomes

BT injection has a high success rate of more than 85% for the management of acute comitant esotropia in children. For congenital esotropia less than 30 prism diopters, the success rate is about 75% after a single injection. Additional injections might be required over time.

Iason Mantagos head shotIason Mantagos, MD, PhD

Assistant Professor of Ophthalmology, Harvard Medical School

Director, Pediatric Ophthalmology and Adult Strabismus Fellowship, Department of Ophthalmology, Boston Children's Hospital and Mass. Eye and Ear