Spatial orientation of motor innervation to the lower orbicularis oculi muscle

Abstract

Background: Blepharoplasty and midface access incisions that are currently used were designed on the premise that innervation to the lower eyelid orbicularis oculi muscle approaches the muscle from its lateral aspect and that its segmental fascicles run parallel to the muscle's fibers. These incisions yield a high rate of complications that include ectropion and other eyelid malpositions. Objective: The goal of this study was to investigate the innervation of the lower orbicularis oculi muscle and determine how it is affected by lower eyelid surgery. Methods: Macroscopic anatomic dissections were performed on 10 frozen cadavers, and the origin and distribution of innervation was mapped. An additional 12 fresh cadaver specimens were dissected through use of 3.5× loupe magnification. Six ultrafresh cadaver specimens were used for histologic examination. Fixation was done in 10% formaldehyde. Axial incisions perpendicular to the facial plane were made at 5-mm intervals from the lower forehead level to the oral commissure. Hematoxylin and eosin specimens and Masson's trichrome specimens were made from alternating slices taken at 5-mm intervals. Results: The results of this anatomic study suggest that the upper eyelid orbicularis oculi muscle is innervated by fascicles of the temporal branch of the facial (VII) nerve. These nerves travel along the undersurface of the muscle and branch out parallel to the muscle fibers. The lower eyelid orbicularis oculi muscle seems to be innervated by 3 to 5 branches of the zygomatic nerve, which splits into 2 large groups of fascicles as it crosses the zygomaticus major muscle. These nerves continue toward the orbicularis oculi muscle, splitting into a plexus of nerves that approaches the orbicularis oculi muscle fibers at an angle of approximately 90°. No significant branches from the lateral aspect of the lower orbicularis oculi were observed in this study. Conclusions: The results of this anatomic study indicate that techniques that (1) approach the midface through the lower eyelid and (2) change the plane of dissection from deep to the orbicularis oculi muscle to superficial to the zygomaticus major muscle may place the innervation of the orbicularis oculi muscle at much higher risk.