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To the Editor We read with special interest the article titled “Botulinum Toxin Type A Injection for Lateral Canthal Rhytids: Effect on Tear Film Stability and Tear Production” by Ho et al1 and offer additional support for the mechanism by which botulinum toxin injection may alter the functioning of the meibomian glands that was not referenced by the authors. Ho and colleagues hypothesize that injection of botulinum toxin type A at the lateral canthus may diffuse to the pretarsal orbicularis and affect the emptying of the meibomian glands. As a diffusion radius of 2 to 4 cm would likely involve the pretarsal orbicularis, the authors hypothesize that “[p]aralysis of these muscles by botulinum toxin will decrease the driving force for meibomian oil excretion.”1 This is based on the pathology of the muscle of Riolan, which is a distinct subdivision of striated orbicularis muscle and is hypothesized to compress the meibomian gland ductules, aiding in expression of their contents.2
Allen RC, Wise RJ. Orbicularis Oculi Weakness and Obstructive Meibomian Gland Disease. JAMA Ophthalmol. 2014;132(12):1490-1491. doi:10.1001/jamaophthalmol.2014.2986