Ophthalmic artery

Origin and course

The ophthalmic artery most commonly arises as the first major branch of the internal carotid artery, directly after emerging from the carotid sinus. It arises from the C6 segment of the internal carotid artery, usually at the level of the anterior clinoid process of the sphenoid bone. After a short intracranial course, the ophthalmic artery pierces the dura and enters the orbit through the optic foramen, traveling through the optic canal alongside the optic nerve. Within the optic canal, the ophthalmic artery begins its course lying inferolaterally to the optic nerve. The artery then crosses over, or rarely, under the optic nerve from lateral to medial sides, giving off its first branch. 

As it emerges from the optic canal, the ophthalmic artery courses anteriorly along the medial wall of the orbit, passing between the superior oblique and lateral rectus muscles. Along its way through the orbit, the ophthalmic artery gives off several branches before dividing into its terminal branches near the upper medial edge of the orbit.

Branches and supply

The branches of the ophthalmic artery can be quite variable, but usually amount to 10 arteries in total; the central retinal artery, muscular branches, posterior ciliary arteries, lacrimal artery, supraorbital artery, posterior ethmoidal artery, anterior ethmoidal artery, medial palpebral arteries, supratrochlear artery, and dorsal nasal artery. 

• Central retinal artery: the first and most important branch of the ophthalmic artery that arises just before the ophthalmic artery crosses over the optic nerve. The central retinal artery supplies the optic nerve, as well as the inner 6/7 layers of the retina.
• Muscular branches: these often form superior and inferior groups and accompany the oculomotor nerve to supply extraocular muscles. Additionally, the muscular branches give off anterior ciliary arteries to supply the ciliary plexus, and anterior conjunctival arteries to supply to conjunctiva.
• Posterior ciliary arteries: consist of two sets of arteries; long and short posterior ciliary arteries. These arteries pierce the sclera on the posterior aspect of the eyeball, just lateral to the optic nerve, and go on to supply the sclera, choroid and anterior segment of the eyeball. The long posterior ciliary arteries end near the sclerocorneal junction by joining the major arterial circle of the iris.
• Lacrimal artery: one of the largest branches of the ophthalmic artery. This artery arises just before the ophthalmic artery enters the orbit. It passes anteriorly along the superior border of lateral rectus muscle, accompanying the lacrimal nerve. The lacrimal artery mainly supplies the lacrimal gland, but also the eyelids, conjunctiva and parts of the dura mater. 
• Supraorbital artery: arises after the ophthalmic artery crosses over the optic nerve. The supraorbital artery exits the orbit through the supraorbital foramen, accompanied by the supraorbital nerve and vein. The part of the supraorbital artery that is within the orbit supplies the superior rectus and levator palpebrae superioris, while its extraorbital part supplies the skin, muscles and periosteum of the forehead.
• Posterior ethmoidal artery: shortly after arising, this branch passes through the posterior ethmoidal canal and into the anterior cranial fossa. Within the cranium, the posterior ethmoidal artery gives off nasal and meningeal branches. The nasal branches descend into the nasal cavity through the apertures of the cribriform plate and supply the posterior ethmoidal cells and the nasal septum. The meningeal branches supply the dura mater of the medial third of the floor of the anterior cranial fossa. 
• Anterior ethmoidal artery: passes through the anterior ethmoidal foramen, accompanied by the nasociliary nerve. Upon entering the cranial cavity, the anterior ethmoidal artery gives off the artery of falx cerebri, that supplies the falx and dura mater, and the nasal branches that descend into the nasal cavity through the cribriform plate to supply the middle and anterior ethmoidal cells, lateral wall of the nasal cavity and the nasal septum.
• The medial palpebral arteries: arise just superior to the trochlea, usually divided into superior and inferior branches for the upper and lower eyelid, respectively.
• Supratrochlear artery: one of the two terminal branches of the ophthalmic artery. It leaves the orbit and ascends superiorly to supply the skin, muscles and periosteum of the forehead.
• Dorsal nasal artery: the second terminal branch of the ophthalmic artery. Along its course, it gives off several branches which supply the nasolacrimal sac and the dorsum of the nose.