After Botulinum Toxin Therapy, Blinking Parameters Do Not Normalize

Botulinum toxin therapy for blepharospasm (BPS) and hemifacial spasm (HFS) significantly reduces blinking frequency but does not normalize blinking parameters such as amplitude or velocity, according to research published in the Journal of Neuro-Ophthalmology.

Although botulinum toxin injections are the standard treatment for BPS and HFS, little data exists regarding the effect on blinking parameters for these patients. The study aimed to assess whether botulinum toxin injections could normalize blinking parameters.

The researchers evaluated 86 eyelids from 49 participants, including 26 with hemifacial spasm, 11 with blepharospasm, and 12 age-matched controls. Patients received injections in the muscles around the eye with an optimized dose of botulinum toxin A. Patients then underwent assessments of their blinking parameters 30 days after treatment using high-speed videography.

The study found that blinking parameters were significantly reduced compared with baseline for the individuals in the BPS group after botulinum toxin injection, including amplitude (22% reduction; P <.001), frequency (21% reduction; P =.04), and maximum closing velocity (41%; P <.001). Blinking parameters were similarly reduced compared with baseline for the HFS group including amplitude (20% reduction; P =.015), frequency (39% reduction; P =.002), and maximum closing velocity (26% reduction; P =.005). 

Blinking frequency became close to normal after treatment. However, eyelid closure velocity (P <.001) and blinking amplitude (P <.05) were lower for treated patients compared with age-matched controls. These data suggest that these patients exhibit slower and incomplete blinks that do not normalize after treatment with botulinum toxin. 

The findings may support a hypothesis that symptoms may be related to a change in the composition of muscle fibers. The study authors hypothesize, “conversion of fast-twitch orbicularis oculi muscle fibers into slow-twitch fibers after years of tonic contractions could explain the reduced blink closing velocity observed on the affected side in HFS, and similarly in BSP patients. Because approximately 10% of normal orbicularis oculi fibers are slow, an increase in their number could lead to a marked reduction in blink closing velocity.”

These results may be limited by the variability of eyelid spasms due to time of day, stress, and other environmental conditions.