Patterns of Oculomotor Nerve Distribution to the Levator Palpebrae Superioris Muscle, and Correlation to Temporary Ptosis After Blepharoplasty

Abstract

Transient diplopia, blepharoptosis, or both conditions are rare postoperative complications of blepharoplasty performed with the patient under local anesthesia. It has been hypothesized that some cases of postoperative diplopia and blepharoptosis could be attributed to the myotoxic effects of local anesthetics to the extraocular muscles and the levator muscle or to the neurotoxic effects of lidocaine. In 30 cadavers, the superior division of the oculomotor nerve was severed en bloc 1.5 cm anterior to the annulus of Zinn with the levator palpebrae superioris (LPS) and the superior rectus muscles. These muscles were detached from their origins, and their attachments to the scleral and tarsal plates were divided respectively. The specimens were treated in guanidine-hydrochloride and Alizarin Red solution, and were dissected under an operating microscope. The nerve branches of the superior division of the oculomotor nerve innervated the proximal third (type I) in 2 of 30 LPS muscles (6.7%), in 8 of 30 muscles (26.7%) extended to the middle third (type II), and reached the distal third (type III) in 20 of 30 muscles (66.7%). The terminal branches ran through the medial third (type IIIa) in 6 of 20 type III LPS muscles (30%), the central third (type IIIb) in 8 muscles(40%), and the lateral third (type IIIc) in 6 muscles (30%). The oculomotor nerve ends that extend forward to the distal third of the LPS muscle (type III) are exposed and vulnerable to local anesthetics and may be numbed during blepharoplasty. If this is so, postoperative blepharoptosis may be caused by transient paralysis of the LPS muscle, and great care should be taken during the injection of local anesthetics near the LPS.