Central retinal artery

Course

The central retinal artery is the first branch of the ophthalmic artery. It originates from the medial surface of the ophthalmic artery either in the optic canal, or after this vessel passes through the optic foramen and has entered the dural sheath of the optic nerve.

From its origin, the central retinal artery passes inferior to the optic nerve, traversing within its dural sheath for a short distance. It then enters the trunk of the nerve itself through its inferomedial surface approximately 6–15 mm behind the eyeball, together with the central retinal vein. These vessels course through the nerve along its axis towards the retina. The artery passes through the papilla of the optic nerve and then through the lamina cribrosa of sclera, to. reach the ninth, nerve fiber, layer of the retina. Here it splits into its terminal branches.

Branches and supply

The central retinal artery supplies the inner two-thirds of the retina. Meaning that the central retinal artery nourishes all the retina except for the photoreceptor layer, this is supplied by choriocapillaris from the choroid.

Upon entering the nerve fiber layer of the retina, the central retinal artery divides into two branches; the superior branch and the inferior branch. These both further subdivide into temporal and nasal terminal arterioles, resulting in four terminal arterioles.

Each of the arterioles supplies one quadrant of the eye. They are named according to their quadrant; superior nasal, inferior nasal, superior temporal, and inferior temporal arterioles. Each arteriole supplies its respective quadrant exclusively and there are no anastomoses between the four of them, which is why they are called functional end-arteries.

The four arterioles course towards the peripheral areas of the eyeball, through the nerve fiber layer, just beneath the internal limiting membrane (the 10th layer of the retina). As they course, they give off collateral branches that dive deeper through the retinal layers and comprise two major capillary networks within their respective quadrants;

• The inner capillary network within the ganglion cell layer (8th layer)
• The outer capillary network within the inner nuclear layer (7th layer)

Note that not every region of the retina receives the same amount of blood. The highest density of capillaries is in the macula, and it decreases towards the periphery of the eye. The capillaries that feed the macula are the branches of the macular arterioles, which stem from all four functional end-arteries. It is important to emphasize that the capillaries from the central retinal artery do not reach the fovea of the retina (capillary free zone). Instead, this area is supplied by the branches of the posterior ciliary arteries that supply the adjacent choroid.

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