Lateral View of the CRA. A, Lateral view of the CRA. The anular tendon has been divided between the superior and lateral rectus muscles. The superior rectus muscle has been elevated and the lateral rectus muscle folded downward to expose the site of origin of the CRA from the ophthalmic artery (yellow arrow) and the point of penetration of the CRA into the optic sheath (blue arrow). Other structures in the exposure include the lacrimal, nasociliary, ophthalmic, and abducens nerves, the inferior division of the oculomotor nerve, and the ciliary ganglion. B, The right optic nerve viewed anterolaterally. The ophthalmic artery enters the orbit on the lateral side of the optic nerve and turns medially above the nerve. The CRA arises in a common trunk with the posterior ciliary artery and passes to the center of the optic nerve. The optic nerve has been sectioned to show the CRA coursing in the center of the nerve distal to where it penetrated the optic sheath. The ophthalmic artery passes above the optic nerve. The ophthalmic artery is divided into three segments based on the two curves of the ophthalmic artery relative to the optic nerve. The first or proximal segment (yellow bracket) extends from the orbital apex and along the inferolateral aspect of the optic sheath. The second segment (blue bracket) begins where the artery curves medially to pass above or below the optic sheath and ends at the point at which it turns forward on the medial side of the sheath. The third segment (not shown) extends forward on the medial side of the optic nerve where it follows a tortuous course. C, The distal third of the optic nerve has been sectioned to show the CRA coursing in the center of the proximal and distal segments of the nerve. D, The CRA arises from the right ophthalmic artery that passes above the optic nerve. The CRA arises in a short trunk with the posterior ciliary artery, penetrates the sheath, and passes to the center of the nerve. E, The ophthalmic artery gives rise to two small branches that penetrate the upper surface of the optic sheath and take a recurrent course toward the orbital apex. F, The ophthalmic artery passes forward below the optic nerve and gives rise to the CRA, which sends a recurrent branch along the sheath toward the orbital apex. This is only one of more than 100 orbits examined in which a branch of the CRA was identified. (Images courtesy of AL Rhoton, Jr.)