Analysis of the nerve branches to the orbicularis oculi muscle of the lower eyelid in fresh cadavers

Background: Scleral show or ectropion is a known complication of lower eyelid surgery. It is particularly problematic after lower eyelid blepharoplasty when the orbicularis oculi muscle is transected or after other procedures are performed that denervate the lower eyelid. The purpose of this study was to determine whether a dominant motor branch exists to the lower lid orbicularis oculi muscle, using anatomic dissection and histologic analysis. Methods: Sixteen fresh facial cadaver halves were dissected using the operative microscope to identify and measure nerve branches. The nerves were then harvested, sectioned, and stained with toluidine blue dye for histomorphometric analysis. Nerves were categorized as either lateral or medial to a vertical line marked at the lateral edge of the limbus of the eye. Results: Eighty-seven percent and 47 percent of cadaver halves had one and two nerve branches lateral to the limbus, respectively. Eighty percent and 47 percent of cadaver halves had one and two nerve branches medial to the lateral limbus, respectively. The nerve branches entered the inferior edge of the orbicularis oculi muscle between 0.88 cm (±0.36 cm) and 2.73 cm (±0.46 cm) from the lateral canthus. There was no correlation noted between fascicular counts and distance from the lateral canthus. Conclusions: Multiple motor nerves exist to the lower eyelid. Branches are found medial and lateral to the lateral limbus, and no nerve branch is dominant.