CHOROIDAL BLOOD FLOW: Review and Potential Explanation for the Choroidal Venous Anatomy Including the Vortex Vein System.

Abstract

To review control mechanisms for blood flow in the choroid, propose a system by which venous outflow is controlled by a Starling resistor, and propose an explanation for the choroidal venous architectural anatomy. The main blood flow control mechanisms were reviewed including autoregulation, neurovascular coupling, and myogenic regulation. Applicable blood flow control mechanisms in the brain, a high flow organ in a low compliance outer shell, were used to examine analogous processes that may be occurring in the choroid. There does not seem to be effective autoregulation in the choroid, although myogenic mechanisms may be present. There is a sophisticated neural innervation that provides partial control. Like the brain, the eye has a high pulsatile blood flow rate and is encased in a noncompliant casing. As part of modulating pulsatile pressure in the cranium, the brain uses venous storage and a Starling resistor effect to modulate venous outflow. An analogous function in the eye could be provided by the choroid, which contains fascicles of large veins that converge in vortices to drain out of the eye. This vortex area seems to be where the Starling resistor effect is possible. This mechanism would have important impact on theories of many ocular diseases including central serous chorioretinopathy and spaceflight-associated neuroocular syndrome. Control of blood flow is critical in the choroid, and this control seems to extend to the venous outflow system. Abnormalities in venous outflow may critically affect function in predictable pathogenic mechanisms.