Side benefit of botulinum toxin A? Decreased IOP in Hemifacial Spasm

Botulinum toxin A (BTX-A) injection for hemifacial spasm (HFS) may have an additional benefit: reduction of contralateral blepharospasm and intraocular pressure (IOP), according to a small Brazilian study.

The mean IOP was 11 ± 3.42 mm Hg before treatment in the affected eye and 9 ± 2.98 mm Hg in the contralateral eye (Pi=0.012). After BTX-A injection, however, no intraocular difference was detected using the Diaton digital interpulse tonometer (Pi=0.204) or the Goldmann surface tonometer (GAT; Pi=0.971), reported Sebastião Cronemberger, MD, of the Federal University of Minas Gerais in Belo Horizonte, Brazil, and colleagues.

The study is the first to use Diaton to measure the effect of blepharospasm on IOP before and after BTX-A treatment, they wrote in International Ophthalmology.

Involuntary blepharospasm is thought to be associated with increased IOP, the only modifiable risk factor for glaucoma, the authors noted. “Therefore, patients with HFS who are suspected of having or have been diagnosed with glaucoma should continue to be monitored periodically with adequate testing after treatment with BTX-A.”

Commenting on the study, Drew Carey, MD, of the Wilmer Eye Institute at Johns Hopkins Medicine in Baltimore, said it’s unclear whether HFS itself causes artificially high IOP. “But it’s been known for a long time that people who squint for a variety of reasons can have artificially higher pressures when measured during glaucoma screening.”

He cautioned, however, that in many cases the apparent IOP elevation may be an artifact of the measurement method.

Regarding a takeaway message about eye treatment, he noted that “this study would not have important clinical implications because most patients with HFS would be getting Botox injections anyway.”

Thus, while the results do not support an immediate strategy to treat other causes of IOP with a neurotoxin, “they may raise awareness in people who are not receiving optimal treatment for HFS that they should consider possible IOP elevation when being screened.” for glaucoma,” he said.

While confirming that the injection lowers IOP and improves patients’ quality of life, Cronemberger’s team noted several issues that need to be addressed. “If these patients were not treated with BTX-A, they would be develop glaucoma, or there would be a decrease in IOP between contractions secondary to increased aqueous drainage caused by convulsions?’

Further studies are needed to answer these questions, they said.

For this single-center study, 27 patients with moderate to severe HFS were measured both before and after BTX-A, the first-line treatment for HFS, from October 2017 to April 2019. The mean age was 59 ,8 years and 63% were women. The right side was affected by HFS in 16 patients, and the duration of symptoms ranged from 1 to 21 years, with a mean of 10 years. Patients with ocular hypertension or glaucoma were excluded.

Participants received a complete ophthalmologic evaluation 10 to 20 days after treatment, when IOP was also measured with GAT (which can be compromised by blepharospasm) and then compared with Diaton results. Participants were also screened for glaucoma with automated perimetry, optical coherence tomography, and pachymetry.

Study limitations included the small population due to the rarity of HFS, short-term follow-up, and the fact that IOP was not measured with GAT before injection.