February 2018

NEWS & OPINION

Research highlight
Possible new use for botulinum toxin in ophthalmology


by Liz Hillman EyeWorld Staff Writer


Botulinum toxin A was found to relieve symptoms of photophobia and dry eye in patients receiving injections for treatment of chronic migraines.
Source: Heather Sered, MD, and Jodi Hwang/Miami Veterans Affairs Neurotoxin Clinic

Research lays groundwork for possible use of drugs that target nerve function to alleviate photophobia and neuropathic dry eye

While the most popular use of botulinum toxin A is cosmetic, there are several medical indications for the neurotransmitter-blocking protein, and recent research could add to
the list.
A study published in Ophthalmology described how botulinum toxin A seemed to relieve photophobia symptoms and sensations of dry eye in some patients receiving injections for treatment of chronic migraines.1
Anat Galor, MD, Miami Veterans Affairs Medical Center, and Bascom Palmer Eye Institute, Miami, corresponding author of the study, said this preliminary research lays the groundwork for future studies that could identify a nerve-associated mechanism behind photophobia and some sensations of dry eye where clinical signs are absent and establish relevant treatments.
In the study, 91 patients who had received botulinum toxin injections for chronic migraines, which is FDA-approved for this indication in patients who have 15 or more headache days a month, were asked to recall their symptoms of photophobia during and between migraine episodes. They were also asked using a numeric scale to rate their migraine, photophobia, and dry eye symptoms before and after starting treatment with botulinum toxin.
Before botulinum treatment, 80% of patients rated photophobia as severe, while 44.4% rated dry eye symptoms as severe. After botulinum treatment, 72.5% of patients reported at least some improvement of photophobia, and 29.3% reported at least some improvement of dry eye symptoms. According to the research, analysis was conducted that showed improvement in these symptoms was more likely in older patients.
This research and other studies, Diel et al. wrote, suggest a shared neural mechanism between migraine pain, photophobia, and neuropathic dry eye, drawing them back to the trigeminal nucleus caudalis and its cervical extension, collectively known as the trigeminal cervical complex.
“We think that botulinum toxin has an effect on the eye by decreasing afferent traffic through other components of the trigeminal system,” Dr. Galor said, later explaining more specifically that they think it’s inhibiting the release of calcitonin gene-related peptide, which is a molecule that starts what she called “the cycle of neurogenic inflammation.”
“What we’re seeing is if you decrease inflammation, you decrease nerve injury, you decrease afferent trafficking, you’re decreasing the information that’s being propagated through the trigeminal system, and that has an effect on decreasing different types of sensations, including the sensation of dryness and pain,” Dr. Galor said.
This research presents a different way of thinking about sensations of dryness and photophobia.
“The main message is sensations of dryness is an umbrella that includes ocular surface abnormalities … and also nerve abnormalities,” Dr. Galor said. “Most people probably have a touch of both, but there are some people who are more on the neuropathic spectrum, where you look at their ocular surface and it doesn’t look that bad but they have sensations of dryness. … I think we need to identify populations based on underlying physiology—are you feeling dry because your eyes are dry or are you feeling dry because your nerves are dysfunctional—and then adapt other treatments that addresses nerve function.”
She continued that this research is not saying that botulinum toxin is the answer for these conditions, per se, but that there is a nerve-associated mechanism and treatments that target that, especially for people who are not responding to topical therapies.
Already brought into the wheelhouse of some ophthalmologists who are beginning to offer aesthetic services, Dr. Galor said the use of botulinum toxin or other similar injections for photophobia or neuropathic dry eye is well within the ophthalmic community’s capabilities in the future. What’s more, it’s already being used in the field, in some cases for medical treatment like blepharospasm or strabismus.
“Many of these are things we don’t routinely think of but that could be easily adopted into ophthalmology clinics,” Dr. Galor said.
Given that this research was based on recall and thus subject to recall bias, Dr. Galor said they are currently conducting a prospective study, getting pre- and post-injection metrics from patients to see if the findings hold. If they do, Dr. Galor said they will try to design studies to further test for photophobia and neuropathic dry eye and perhaps optimize protocols for targeting these possible treatments.

Reference

1. Diel RJ, et al. Botulinum toxin A for the treatment of photophobia and dry eye.
Ophthalmology. 2018;125:139–140. 

Editors’ note: Dr. Galor has no financial interests related to her comments.

Contact information

Galor: AGalor@med.miami.edu

Possible new use for botulinum toxin in ophthalmology Possible new use for botulinum toxin in ophthalmology
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