Figure 1. Location of the retina within the eye (A) and retinal blood vessels within the retina (B).

(A) Schematic cross-section of the posterior part of the eye around the optic nerve shows the macula which is located temporal to the optic nerve and is responsible for our best vision. The foveal pit or depression is located in the center of the macula and is the area needed for the very best vision. The round blow up on the left shows that the multilayered retina sits on the retinal pigmented epithelium (RPE) which sits on Bruch’s membrane. The central retinal artery enters through the optic nerve, sends numerous branches along the surface of the retina to the peripheral edges of the retina. The arterioles enter capillaries which enter venules and then veins that run along the surface of the retina and enter the central retinal vein that exits through the optic nerve.

(B) A further blow up of the retina shows that the retinal arteries branch to form the superficial capillary bed near the surface of the retina and send penetrating branches to form the intermediate and deep capillaries. The outer third of the retina which consists of the photoreceptor outer and inner segments and cells bodies is avascular. It receives oxygen and nutrients from the choroidal circulation. Large choroidal vessels branch and become progressively smaller until they form the choriocapillaris which is fenestrated and allows plasma to pool along Bruch’s membrane. The RPE, which has barrier characteristics prevents fluid from entering the outer retina but allows oxygen and nutrients to enter.