BLOOD-SUPPLY OF THE RETINA

An overview of the functional anatomy of the retinal microcirculatory system and its regulation mechanisms is presented. The retinal microva sculature is characterized by thin capillaries which leave large vesse l-free spaces compared to other microvascular beds. Despite high blood flow velocities, the blood now volume within the capillaries is relat ively low. This results in a high arteriovenous pO(2) difference and a small capacity to tolerate periods of low perfusion. Furthermore, fro m the optic nerve head on there is no autonomic perivascular innervati on to control the microvascular tone. A control via the bloodstream (m ediators, e.g. O-2, CO2, hormones), astrocytes, neurites and Muller ce lls (mediators, e.g. NO, prostaglandins, neuropeptides) takes over. Fi nally, the role of pericytes in the control of retinal hemodynamics is discussed.