Cellular and physiological mechanisms underlying blood flow regulation in the retina and choroid in health and disease

Abstract

We review the cellular and physiological mechanisms responsible for the regulation of blood flow in the retina and choroid in health and disease. Due to the intrinsic light sensitivity of the retina and the direct visual accessibility of fundus blood vessels, the eye offers unique opportunities for the non-invasive investigation of mechanisms of blood flow regulation. The ability of the retinal vasculature to regulate its blood flow is contrasted with the far more restricted ability of the choroidal circulation to regulate its blood flow by virtue of the absence of glial cells, the markedly reduced pericyte ensheathment of the choroidal vasculature, and the lack of intermediate filaments in choroidal pericytes. We review the cellular and molecular components of the neurovascular unit in the retina and choroid, techniques for monitoring retinal and choroidal blood flow, responses of the retinal and choroidal circulation to light stimulation, the role of capillaries, astrocytes and pericytes in regulating blood flow, putative signaling mechanisms mediating neurovascular coupling in the retina, and changes that occur in the retinal and choroidal circulation during diabetic retinopathy, age-related macular degeneration, glaucoma, and Alzheimer's disease. We close by discussing issues that remain to be explored.

Effects of carotid baroreceptor stimulation on retinal arteriole remodeling evaluated with adaptive optics camera in resistant hypertensive patients

“…Contrary to choroidal vasculature, retinal microcirculation is characterized by the absence of any sympathetic stimuli influence [17]. While baroreflex activation decreases peripheral resistance in sympathetic-stimuli-responder territories, it has no effect on retinal vascular resistance.…”

Leveraging Optogenetic-Based Neurovascular Circuit Characterization for Repair

“…Multiple mechanisms have been proposed for neurovascular regulation of blood vessels in healthy retina, including arachidonic acid metabolites, nitric oxide (NO), and acetylcholine (ACh) [18,[23][24][25][26]. Among numerous neurotransmitters, ACh is believed to play a central role.…”

Changes in Choroidal Thickness after Hemodialysis and the Influence of Diabetes

“…The choroid is a highly vascularized structure derived primarily from the long and short ciliary arteries with some contribution from the anterior ciliary arteries [1,2]. The main function of the choroid is supplying oxygen and nutrients to the outer retina [1,3,4].…”

“…Choroidal circulation is under neurogenic control [1,2]. Sympathetic innervation includes both noradrenergic and neuropeptide fibers [1,2,5,6].…”

“…Sympathetic innervation includes both noradrenergic and neuropeptide fibers [1,2,5,6]. Parasympathetic innervation is primarily cholinergic [1,2,6].…”