A, Right ophthalmic artery origin from the clinoid segment of the internal carotid artery. The ophthalmic artery usually arises just above the clinoid segment, but in this case, the artery arises from the clinoid segment below the anterior clinoid process, which has been removed. The artery passes through the superior orbital fissure between the oculomotor and ophthalmic nerves. The lateral wall of the right cavernous sinus and the anterior clinoid process have been removed to expose the intracavernous and clinoid segments of the internal carotid artery, and the ophthalmic nerve has been retracted to expose the inferolateral trunk. B, Ophthalmic artery origin in the cavernous sinus. Lateral aspect of a right ophthalmic artery that arises from the intracavernous segment of the left internal carotid artery. The upper half of a segment of the ophthalmic nerve has been removed to expose an ophthalmic artery. The anterior clinoid artery has been removed to expose the clinoid segment in the interval between the optic and oculomotor nerves. C, The medial rectus muscle has been divided near the globe and reflected posteriorly to expose an ophthalmic artery that courses below the optic nerve to reach the medial part of the orbit, as occurs in approximately 15% of orbits. The branch of the inferior division of the oculomotor nerve to the medial rectus muscle enters the medial side of the muscle. The anterior ethmoidal artery courses below the superior oblique muscle to reach the anterior ethmoidal canal. D and E, duplicate left ophthalmic arteries. D, Superior aspect of a duplicate ophthalmic artery. The levator and superior rectus muscles have been reflected medially and the lateral rectus muscle has been reflected laterally to expose the left optic nerve and the duplicate arteries. The upper duplicate artery arises from the supraclinoid segment of the internal carotid artery, passes through the optic canal to enter the orbital apex on the lateral side of the optic nerve, and courses below the optic nerve to reach the medial part of the orbit. The lower duplicate artery arises from the internal carotid artery in the cavernous sinus, passes through the superior orbital fissure on the lateral side of the optic nerve, and crosses above the nerve to reach the medial part of the orbit. E, Lateral view. The annular tendon has been opened between the superior and lateral rectus muscles. The duplicate artery arising above the cavernous sinus passes forward and downward to course below the optic nerve. The duplicate artery arising in the cavernous sinus passes above the optic nerve. (Images courtesy of AL Rhoton, Jr.)