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Botulinum toxin type A (Botox Cosmetic, Allergan) injected into the periocular region for the treatment of lateral canthal rhytids, usually does not suppress tear production. However, surgeons should warn patients that temporary dry eye is a possibility, although a rare occurrence.
Dr. Yen and colleague Yonca O. Arat, MD, also of the Cullen Eye Institute, undertook a study to evaluate the incidence of dry eye and the effects on tear production after treating patients with botulinum toxin for crow's feet. In 13 patients aged 31 to 58 years, they injected a moderate dose of 10 units of botulinum toxin per side with two separate injections. Using the Schirmer test to measure tear production, they assessed the patients at baseline (before injections), at 1 week, 1 month, and 4 months after the cosmetic treatment.
"In our study, we showed that botulinum toxin's effect in terms of inducing temporary dry eye was not statistically significant," explained Dr. Yen, a specialist in ophthalmic plastic, lacrimal, and orbital surgery. "No statistical difference was found in Schirmer test results from baseline at 1 week, 1 month, and 4 months after injection." The study results were published in Ophthalmic Plastic and Reconstructive Surgery (2007;23:22-24.)
Botulinum toxin, a neurotoxin, works by blocking the release of acetylcholine from the nerves. According to the product information from the manufacturer, when injected into the muscles, botulinum toxin is able to produce partial chemical denervation of the muscle and reduce the muscle activity at the site of the injection.
"Botulinum toxin takes about 2 to 3 days for the first effects to become noticeable and probably 7 to 10 days for the full effects to be realized," explained Dr. Yen. "It is a temporary treatment lasting 3, 4, or 5 months. The neuron recovers and is able to release acetylcholine after a given amount of time."
The key to avoiding the complication of temporary dry eye with botulinum toxin is knowledge of the anatomy.
"Proper placement of the injections should avoid the pretarsal muscle fibers of the upper eyelid so as to reduce the risk of affecting eyelid blinking as well as the superior lateral orbit where the lacrimal gland is located," Dr. Yen said.
In a report published in the American Journal of Ophthalmology (2000;129:481-486), the investigators discovered that botulinum toxin injections into the medial part of the upper and lower eyelids had an effect on the lacrimal gland. The eyelids exhibited reduced blink, and there was decreased lacri mal gland drainage. "The lacri mal gland needs to be stimulated to produce and secrete tears," Dr. Yen noted. "The botulinum toxin would inhibit the stimulation of the lacrimal gland."
Surgeons need to know the periorbital anat o my, know where to place the injections, know the proper plane to inject into, and must not inject too deeply to go into the orbit or lac ri mal gland. "The key is that the physician really needs to know how the medication works, where the optimal placement of the medication is in terms of treating the wrinkles, using the proper technique to place the medication in the proper muscles, and being aware of potential complications and how to manage them should they occur," Dr. Yen explained.
Dr. Yen said that some limitations to the study included no control group, the variability of the Schirmer test results, no evaluation of the ocular surface with fluorescein staining, and the fact that the same dose of botulinum toxin was used in all patients.
"Obviously, some patients [in clinical practice] may require a higher dose of botulinum toxin," he said. "A greater total amount of toxin injected or a larger volume of injection could conceivably result in a higher incidence of lacrimal gland involvement and a subsequent decrease in tear production."
Botulinum toxin injection is the most common cosmetic procedure performed because of its excellent success rate, convenience, and minimal down time, so patients should be advised of all the potential complications, including the risk of temporary dry eye, Dr. Yen concluded.