Blood supply of the retina.

An overview of the functional anatomy of the retinal microcirculatory system and its regulation mechanisms is presented. The retinal microvasculature is characterized by thin capillaries which leave large vessel-free spaces compared to other microvascular beds. Despite high blood flow velocities, the blood flow volume within the capillaries is relatively low. This results in a high arteriovenous pO2 difference and a small capacity to tolerate periods of low perfusion. Furthermore, from the optic nerve head on there is no autonomic perivascular innervation to control the microvascular tone. A control via the bloodstream (mediators, e.g. O2, CO2, hormones), astrocytes, neurites and Müller cells (mediators, e.g. NO, prostaglandins, neuropeptides) takes over. Finally, the role of pericytes in the control of retinal hemodynamics is discussed.