Macular Circulation

The macular circulation is one of the most active circulatory systems in the entire body. There are two sources of blood supply to the human retina. These sources include the central retinal artery and the choroidal blood vessels.

The choroid is a layer of tissue behind the retina. The blood circulation in the choroid supplies almost 85% of the oxygen to the retina. The circulation in the choroid supplies oxygen to the outer layer of the retina where photorectors are located.

The ophthalmic retinal artery supplies the remaining oxygen supply to the retina. The ophthalmic retinal artery travels into the eye through the optic nerve. It then separates into four main branches to supply the inner surface of the retina. The four major branches separate in a radial fashion at the surface of the optic nerve head. All four branches are important for macular circulation.

The inner structure of the retina has three layers of capillaries. These include the radial peripapillary capillaries, the inner capillary layer, and the outer capillary layer. A network of venous capillaries drain the intraretinal layer into the central retinal vein.

The radial peripapillary capillaries constitute the most superficial layer in capillaries in the inner part of the retina. These capillaries travel along the upper and lower portions of the macular region. The inner capillary layer nourishes that part of the retina known as the ganglion layer. The outer capillary network nourishes the outer portion of the retina. The layer of the retina supplied by the outer capillary layer is knwn as the inner plexifirm layer.

A ring of capillaries travels in the outer perimeter of the macula. But the center of the macular is free of capilaries. The capillary-free zone is about 450 to 600 microns in diamteter. This capillary-free zone is also known as the fovea.

The choroid derives its circulation from from long and short posterior ciliary arteries and branches of Zinn’s circle of arterioles arnound the optic disc. Each posterior ciliary artery becomes a fan-shaped network of capillaries that supplies different areas of the choroid.

The posterior ciliary arteries from the ophthalmic artery enter the sclera near the optic nerve. They disperse to form three vascular lasyers in the choroid. These network layers include the outer choroid, medial choroidal layer, and the inner choroidal layer. The inner network is close to Bruchs membrane and the retina pigment epithelium. The vortex veins pass through the white sclera and merge to form the ophthalmic vein.

The macular circulation is a complex network of blood vessels. Research in macular degeneration will inevitably provide additonal details regarding the influence of blood flow in macular degeration.

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