Retinal Vasculature and Oxygen Supply
The vascular supply of the retina comes from the retinal circulation for the inner retina, and indirectly from the choroidal circulation for the avascular outer retina. The central retinal artery (a branch of the ophthalmic artery) enters the eye and divides into 4 branches, each supplying blood to a quadrant of the retina. These branches are located in the inner retina. Occasionally, a cilioretinal artery, derived from the ciliary circulation, will supply a portion of the inner retina (Fig 1-8). On a tissue level, the retina is supplied by up to 4 layers of vessels: the radial peripapillary capillary network located in the nerve fiber layer and around the optic nerve head, the superficial vascular plexus in the retinal ganglion cell layer, and the deep capillary plexus with 2 capillary beds, one on either side of the INL. Although the superficial layer of the deep capillary plexus is sometimes referred to as the intermediate capillary plexus, typically both layers are collectively referred to as the deep capillary plexus. With the advent of OCT angiography, which is able to visualize these distinct capillary layers, interest in this anatomy has grown. The retinal vasculature, including its capillaries, retains the blood–brain barrier with tight junctions between capillary endothelial cells. Blood from the capillaries is collected by the retinal venous system; it eventually leaves the eye through the central retinal vein by way of branch retinal veins.
The outer retinal layers, beginning with the outer plexiform layer, derive their oxygen supply from the choroidal circulation. The exact boundary between the retinal vascular supply and the diffusion from the choriocapillaris varies according to the topographic location, retinal thickness, and amount of light present. See also the section Choroid later in this chapter, as well as Part I, Anatomy, of BCSC Section 2, Fundamentals and Principles of Ophthalmology.
Figure 1-8 A central retinal artery occlusion in a young patient with a previously unknown patent foramen ovale. Presumably, an embolus from the systemic circulation passed through the patent foramen ovale and lodged in the central retinal artery, occluding its blood flow. Fortunately, a cilioretinal artery supplied part of the eye’s retina. Note the retinal ischemic whitening in the distribution of the central retinal artery but preservation of the normal retinal transparency in the zone supplied by the cilioretinal artery.
(Used with permission from Ho IV, Spaide RF. Central retinal artery occlusion associated with a patent foramen ovale. Retina. 2007;27(2):259–260.)
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.