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Superior Views of Right and Left Orbital Apexes and Surrounding Structures

Surgical Correlation

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Superior views of right and left orbital apexes and surrounding structures. The optic canals lie just medial to the anterior clinoid processes and transmit the optic nerve, with its nerve sheath, and ophthalmic artery to the orbit. This canal and a portion of the superior orbital fissure is enclosed by the annulus of Zinn, a common proximal attachment site for the recti muscles. The optic, oculomotor, abducens, and nasociliary nerves and the ophthalmic artery pass through this ring to enter the orbit. The trochlear nerve, frontal nerve, lacrimal nerve, and superior ophthalmic vein enter outside this ring. A superficial strata of extraocular muscles can be seen in each orbit: superior oblique muscles follow the medial wall, lateral rectus muscles follow the lateral wall, and the levator palpebrae superioris muscles course forward between these to the upper eyelid. The superior rectus muscles lie deep to the levator, and the medial rectus muscles lie deep to the superior oblique. The ophthalmic nerve typically gives rise to its "NFL" branches (nasociliary, frontal, lacrimal), which then enter the orbit through the superior orbital fissure. The lacrimal nerve courses along the lateral wall of the orbit (near the superior border of the lateral rectus) to the lacrimal gland. The frontal nerve courses forward in the orbit superficial to the levator palpebrae superioris and superior rectus muscles before dividing into the supraorbital and supratrochlear branches. At the apex of the orbit, the trochlear nerve bends medially (medial to the frontal nerve) to enter the superior border of the superior oblique muscle. The posterior ethmoidal artery, a branch of the ophthalmic artery, is seen passing through a foramen on the medial wall of the orbit to supply ethmoid and sphenoid sinuses before entering the nasal cavity. The floor (greater wing of sphenoid bone) of the middle fossa is intact on the left side of the image. This bone has been removed on the right side to reveal the lateral pterygoid muscle and mandibular nerve in the infratemporal fossa. (Image courtesy of AL Rhoton, Jr.) 

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