Microsurgical Anatomy of the Orbit: The Rule of Seven
Figure 6
(a) Dissection of the left orbit has proceeded from the point seen on Figure 3(a). The periorbit and orbital fat have been dissected and the anterior clinoid removed, to expose the orbital apex. (b) The optic strut separates the optic canal and the superior orbital fissure. Seven are the orbital nerves: optic, oculomotor, trochlear, frontal, lacrimal, nasociliary, and abducens nerves. With the exception of the optic nerve which transits through the optic canal, all others pass along the superior orbital fissure. In the orbital apex, the trochlear nerve and the ophthalmic division of the trigeminal nerve are the most superficial structures. The ophthalmic division gives off the lacrimal nerve, which courses towards the lacrimal gland and the frontal nerve. (c) The frontal nerve gives further the supraorbital and supratroclear divisions. The troclear nerve, which also courses outside the annulus, reaches the superior oblique muscle, on the medial part of the orbit. (d) The nasociliary nerve, the third part of the ophthalmic division, arises from its medial surface and separates into nasal and ciliary portions along the orbital apex. (e) The nasal part passes inside the annular tendon, above the optic nerve, and directs to the medial orbital wall to forms the anterior and posterior ethmoidal nerves (Insert). The ciliary part also enters the orbit deep to the annulus and, in the lateral space of the orbit, forms the sympathetic root of the ciliary ganglion and the long ciliary nerves. The sympathetic fibers emerge without synapsing in the ciliary ganglion. (f)–(h) The abducens and oculomotor nerves are found medially. The abducens is formed by the union of several twigs inside the cavernous sinus. It passes inside the annulus and, in the orbit, ends up spreading along the inner surface of the rectus lateralis muscle (g). At the orbital apex, the oculomotor nerve separates into superior and inferior divisions. The superior division courses deep to the annulus, directs above, and supplies the superior muscular complex, comprising the levator palpebrae and superior rectus muscle (g). The inferior division, coursing near the orbital floor, supplies the inferior and medial recti and the inferior oblique muscle. From the branch directed to the inferior oblique muscle, an ascending twig reaches the ciliary ganglion (g and h), forming its parasympathetic root. The parasympathetic fibers synapse in the ganglion and continue as the short ciliary nerves to the pupillary sphincter.
