7. Reflect the levator palpebrae superioris and superior rectus muscle and remove orbital fat to expose the orbital nerves and vessels.
Next, isolate the levator palpebrae superioris and superior rectus muscle. They should be divided and reflected at their mid-belly. As you reflect the proximal portion of these muscles, look for the superior division of the oculomotor nerve. Immediately deep to these muscles, you will see branches of the ophthalmic vein, which may be removed to complete the dissection. Next, carefully isolate the optic nerve. Note that it is embedded in fat. Do not remove the fat from this area because the ciliary nerves and vessels can be found within this fat. Simply identify the optic nerve. In order to complete the next portion of this dissection, you must cut the muscular anulus. It is to be cut between the lateral and superior rectus muscle. Once you have cut it look for the abducens nerve, passing through the cavernous sinus lateral to the carotid artery. Follow it through the muscular anulus to the superomedial surface of the lateral rectus muscle, shown here. Turn your attention once again to the structures entering the orbit posteriorly. There is the optic nerve, the oculomotor nerve, lying superficial, the trochlear nerve, below that, the ophthalmic division of the trigeminal nerve. Again identify the branches of the ophthalmic nerve, the supratrochlear, and supraorbital nerves. Laterally, the lacrimal nerve to the lacrimal gland. Retract these laterally to expose the superior rectus and levator palpebrae superioris muscle. Reflect these muscles forward and backward. On the deep surface of the proximal portion of these muscles, identify the superior division of the oculomotor nerve. This division supplies only the superior rectus and levator palpebrae superioris muscles. Retract the ophthalmic division and as you do so, note the nasociliary nerve coming off of its medial side and passing toward the nasal cavity. It crosses superior to the optic nerve. As it does so, it gives branches to the back of the eyeball called long ciliary nerves. It sends branches into the ethmoid air cells, the anterior and posterior ethmoidal branches and it terminates as a small nerve on the face called the infratrochlear nerve. The long ciliary nerves are sensory to the eyeball. Immediately above the nasociliary nerve, look for the ophthalmic artery. Recall that it arises from the internal carotid artery and passes through the optic canal with the optic nerve. It passes lateral to the optic nerve and crosses over the top of it like the nasociliary nerve and has similar branches. As it passes along the lateral side of the optic nerve, it gives rise to a branch to the optic nerve. This branch is called the central artery of the retina. Return your attention to the oculomotor nerve. Now follow its inferior division, which passes under the optic nerve. It supplies the inferior rectus muscle, the medial rectus muscle, and inferior oblique muscle. It has connections to a parasympathetic ganglion called the ciliary ganglion that lies lateral to the optic nerve. The oculomotor nerve contains the parasympathetic fibers of the ciliary ganglion. The ciliary ganglion is also connected to the nasociliary nerve via a sensory root. The ganglion is shown here. The ganglion gives rise to short ciliary branches. These contain parasympathetic, sensory, and sympathetic fibers to the blood vessels of the eye.