The first major branch of the internal carotid as it leaves the cavernous sinus. There are variations of anatomy in which it branches prior to the internal carotid leaving the cavernous sinus.
Via its branches, the OA supplies all the structures in the orbit, which it enters with the optic nerve through the optic canal. Proximal to (before entering) the optic canal, the OA is bathed in CSF (qv) and subject to ICP (qv). This segment is called the proximal OA. Distal to (after leaving) the optic canal it branches to supply structures in the nose, face and meninges. This segment is called the distal OA. The distal OA is not surrounded by CSF and not subject to ICP, unlike the proximal OA.
The distal OA gives rise to the ciliary arteries and the central retinal artery (CRA). The CRA, important for normal vision, typically originates as the first branch of the OA. It that penetrates the optic nerve about 1.2-1.3 cm behind the eye and runs within it.« Back to Glossary Index