The blood–retinal barrier, or the BRB, is part of the blood–ocular barrier that consists of cells that are joined tightly together to prevent certain substances from entering the tissue of the retina. It consists of non-fenestrated capillaries of the retinal circulation and tight-junctions between retinal epithelial cells preventing passage of large molecules from choriocapillaris

Choriocapillaris

The capillary lamina of choroid or choriocapillaris is a layer of capillaries that is immediately adjacent to Bruch's membrane in the choroid....

 into the retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

.

Components

The blood retinal barrier has two components: the retinal vascular endothelium and the retinal pigment epithelium. Retinal blood vessels that are similar to cerebral blood vessels maintain the inner blood-ocular barrier. This physiological barrier comprises a single layer of non-fenestrated endothelial cells, which have tight junction

Tight junction

Tight junctions, or zonula occludens, are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates...

s. These junctions are impervious to tracer

Tracer

Tracer may refer to:* Histochemical tracer, a substance used for tracing purposes in histochemistry, the study of the composition of cells and tissues...

, so many substances can impact the metabolism of the eyeball. The retinal pigment epithelium maintains the outer blood–retinal barrier.

Diabetic retinopathy

Diabetic retinopathy

Diabetic retinopathy

Diabetic retinopathy is retinopathy caused by complications of diabetes mellitus, which can eventually lead to blindness....

, eye damage that frequently occurs as a result of diabetes, is related to the breakdown of the blood–retinal barrier. The barrier becomes more leaky in patients with diabetic retinopathy.

Animal studies

Animal model

Animal model

An animal model is a living, non-human animal used during the research and investigation of human disease, for the purpose of better understanding the disease without the added risk of causing harm to an actual human being during the process...

s have shown that the blood–retinal barrier becomes more permeable to substances in hypertensive

Hypertension

Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

 animals (those with high blood pressure

Blood pressure

Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

).