Evaluation of nerve innervation distribution of orbicularis oculi muscle for botulinum neurotoxin application using Sihler's method

Abstract

Background: Blepharospasm is the involuntary and forced closure of the eyelids due to spasm-like contraction of the orbicularis oculi muscle around the eye. The study aimed to reveal the nerve innervation of the orbicularis oculi muscle for Botulinum neurotoxin (BoNT) treatment of blepharospasm by Sihler's staining technique.

Methods: This study used six cephalus (12 orbicularis oculi muscles) with an average age of 69,6 (62-88) years. Then, the orbicularis oculi muscles were removed by dissection, and Sihler's staining technique was applied to the muscles. The limit for dissection of the muscle is the orbital opening level, where the nerves enter the muscle, and the muscle attaches to the bone.

Results: In the region above the palpebral fissure, the nerves entering the muscle were densely located in the superolateral quadrant between 9 and 12 o'clock in the right eye and between 12 and 3 o'clock in the left eye. In the region under the palpebral fissure, the nerves' density in the orbicularis oculi muscle was higher between 4 and 7 o'clock in the right eye and between 5 and 8 o'clock in the left eye.

Conclusion: This study unveiled the nerve branches associated with the orbicularis oculi muscle. It pinpointed precise crossing points of these nerve branches, which can be targeted for applying BoNT in treating blepharospasm. Consequently, by utilizing minimal BoNT, it is anticipated that the quantity of toxin administered will decrease, leading to more efficient outcomes and reduced expenses. Furthermore, this approach can aid in averting potential undesired complications during BoNT administration.

Keywords: Blepharospasm; Botulinum neurotoxin; Nerve innervation; Orbicularis oculi muscle; Sihler’s staining.