Innervation Features of the Extraocular Muscles

Several transcranial surgical approaches such as frontoorbital, lateral, medial, central, inferolateral, and transmaxillary orbitotomy have been used for exposure of lesions within the orbit. During surgical approaches, detailed anatomic knowledge regarding neural, muscular, and neighboring structures for preservation of the neurovascular structures is important in avoiding traumatic retraction of the nerves of the extraocular muscles. For this study, a total of 22 formalin-fixed cadavers were dissected. Vascular structures were perfused with colored latex to facilitate their definition. In this study, the orbit was investigated in two divisions, superior and inferior. In the superior division, innervation features of the levator palpebrae superioris, the superior rectus, and superior oblique muscles were examined. In the inferior division, innervation features of the medial rectus, the lateral rectus, the inferior rectus, inferior oblique muscles, and ciliary ganglion were investigated. The diameter of the oculomotor nerve (CN3) within the superior orbital fissure was measured as 2.10 mm on the right and 2.09 mm on the left. The diameter of the superior division of the CN3 was on average 1.54 +/- 0.30 mm on the right and 1.65 +/- 0.30 on the left. The mean diameter of the inferior division was measured as 1.85 +/- 0.22 mm on the right and 1.94 +/- 0.20 on the left. In the lower wall of the orbit, different branching types of inferior division of CN3 were observed. The diameter of the trochlear nerve in the superior orbital fissure was on average 1.15 +/- 0.19 mm on the right and 1.21 +/- 0.21 mm on the left. The diameter of the abducens nerve in the superior orbital fissure was on average 1.54 +/- 0.24 mm on the right and 1.54 +/- 0.22 on the left. The number of small branches entering the muscle was on average three branches. Areas nervosa of the nerves were located in the middle one third of the muscles. In this study, detailed knowledge regarding the innervation features of extraocular muscles was attained. An understanding of the innervation features of extraocular muscles is important for the preservation of neural structures during intraorbital procedures.