Retinal vasculature structure and function

The inner retina is supplied from the retinal vasculature, which gets it input from the central retinal artery (CRA). At the optic disc that CRA bifurcates into several branches that provide the blood supply of the entire inner retina. The venous part of the retinal circulation is arranged in a similar way. The central retinal vein leaves the eye through the optic disc and drains blood into the cavernous sinus. The diameter of the CRA before it enters the eye as well as the diameters of the branch arteries is typically below 200 mm. Hence, these vessels are functionally arterioles, and the venous vessels are functionally venules. The larger retinal arteries are surrounded by an avascular zone, because the surrounding tissue receives its oxygen from diffusion through the vessel wall. The capillary network of the retina is organized in two layers. The inner layer lies within the nerve fiber and RGC layer and is called inner plexus, whereas the outer layer lies within the inner nuclear and outer plexiform layers and is called outer plexus. Locally restricted to the region around the optic nerve head is a third capillary layer that is located in the nerve fiber layer consisting of radial peripapillary capillaries.