Anatomy of the Ocular Vasculatures

Core Messages

•The human eye is an incredible assembly of unique types of tissues, each of which has its own requirements in terms of blood supply.

•The major source of blood for the anterior eye is the anterior ciliary arteries, whereas the central retinal artery and the posterior ciliary arteries, both originating from the ophthalmic artery, is the supply for the posterior eye.

•The iris receives its arterial blood supply from the major arterial circle (MAC). The iris vessels are radially oriented with slightly sinuous courses, which allow them to accommodate to the movements of the pupil. The iris venous channels roughly follow the arterial ones. The collector trunks from these

G.A. Lutty, Ph.D. (*) • D.S. McLeod

Wilmer Ophthalmological Institute, Johns Hopkins Hospital, M041 Smith Building, 400 North Broadway, Baltimore, MD 21287-9115, USA

e-mail: glutty@jhmi.edu; dmcleod1@jhmi.edu

I. Bhutto, M.D., Ph.D.

Wilmer Ophthalmological Institute, Johns Hopkins

Hospital, M041 Smith Building, 400 North Broadway,

Baltimore, MD 21287-9115, USA

Department of Ophthalmology, Wilmer Eye Institute, Johns Hopkins Hospital, M041 Smith Building, 400 North Broadway, Baltimore, MD 21287-9115, USA e-mail: ibhutto1@jhmi.edu

veins enter the ciliary body, where the blood then drains into the vortex system and the ciliary plexus.

•The ciliary body, a part of the uveal tract, is the circumferential tissue posterior to the iris composed of the ciliary muscle and ciliary processes. Its blood supply is the same as iris but the capillaries of the ciliary processes are large and fenestrated like the choriocapillaris.

•There are two sources of blood and nutrient supply for the human retina: the central retinal artery and the choroidal blood vessels. The choroid receives the greatest blood flow (65-85%), which is vital for maintenance of the outer retina. The remaining 20-30% flows to the retina through the central retinal artery in the optic nerve head to nourish the inner retinal layers.

•There are three layers of capillaries in retina: 1) the radial peripapillary capillaries (RPCs) around the optic nerve head only; 2) the inner or superficial plexus; and 3) the outer or deep layer of capillaries. The retinal vasculature is end-arterial: blood moves from artery to arteriole to capillary and precapillary venules drain into venules and then veins. A blood-retinal barrier exists.

•The only avascular area of retina is the foveal avascular zone where the foveolar