Vertically oriented suborbicular nerve fibers are frequently encountered during upper eyelid surgery. It has not been well established whether these fibers are terminal motor branches of the facial nerve (VII) or sensory branches of the ophthalmic nerve (V-1). To investigate the origin of these nerve fibers, three different techniques were used: (1) intraoperative nerve stimulation; (2) cadaver dissection; and (3) immunohistochemical analysis. The results of all three investigative methods are in agreement and conclusively demonstrate that these fibers represent sensory branches of the ophthalmic nerve (V-1) and not motor branches of the facial nerve (VII). Anatomical dissection showed that the sensory fibers to the upper eyelid do not travel solely within the suborbicular fascial plane, but also course in the preorbicular plane and within the orbicularis muscle itself. The terminal branches of the facial nerve to the upper eyelid innervate the orbicularis oculi from the undersurface and in a horizontal orientation. Clinical correlation of these findings is discussed.
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