Blood Supply of the Retina

Abstract

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 vesselfree spaces compared to other microvascular beds. Despite high blood now 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.

Diabetes-Induced Inhibition of Voltage-Dependent Calcium Channels in the Retinal Microvasculature: Role of Spermine

“…Consistent with the requirement that blood vessels minimally interfere with light, the retina has a relatively low density of capillaries. 1 However, this paucity of microvessels leaves little functional reserve for the vital task of matching local perfusion to metabolic demand. Thus, efficient coupling of blood flow to meet local needs is particularly important in the retina.…”

Oxidative Stress Induced Damage of the Human Retina: Overview of Mechanisms and Preventional Strategies

“…This contains special proteins and hyaluronic acid (Acharya et al, 2000;Hollyfield, 1999;Hollyfield et al, 2001) and the outer segments "bathe" in a sea of plasma, which is supplied by the sea of blood within the choriocapillaries (fenestrated capillaries) and choroid (Funk, 1997). The membrana limitans externa serves as watershed zone between both regions.…”

A novel mechanism for regulation of retinal blood flow by lactate: gap junctions, hypoxia, and pericytes

“…For example, in the kidney, pericytes in the descending vasa recta are important in regulating the distribution of blood flow between the juxtamedullary cortex and the inner and outer medulla (6). The retina has a very high density of pericytes, and these cells appear to play an important role in the regulation of retinal blood flow as well (1,4). As noted by Yamanishi and coworkers (9) in the introduction to their study in this issue of the American Journal of Physiology-Heart and Circulatory Physiology, the low density of retinal microvessels, which is crucial to allow passage of light, introduces problems in regulating blood flow and oxygen delivery to the cells.…”

“…As noted by Yamanishi and coworkers (9) in the introduction to their study in this issue of the American Journal of Physiology-Heart and Circulatory Physiology, the low density of retinal microvessels, which is crucial to allow passage of light, introduces problems in regulating blood flow and oxygen delivery to the cells. This occurs because the volume of blood flow in the retinal capillaries is relatively low, despite the high flow velocity in individual vessels (4). This leads to a relatively large arteriovenous O 2 difference and makes the retina particularly vulnerable to reduced perfusion and other conditions that could lead to decreased tissue PO 2 (4).…”

“…This occurs because the volume of blood flow in the retinal capillaries is relatively low, despite the high flow velocity in individual vessels (4). This leads to a relatively large arteriovenous O 2 difference and makes the retina particularly vulnerable to reduced perfusion and other conditions that could lead to decreased tissue PO 2 (4). Pericytes may be involved in a number of vascular abnormalities that occur in the retina with different diseases, such as hypertension, diabetes, and glaucoma (1).…”