Blood–retinal barrier

Blood–retinal barrier is a part of the eye that prevents certain substances from entering the retina. It is similar to the blood–brain barrier and is composed of two components: the inner blood-retinal barrier and the outer blood-retinal barrier.

Structure

The inner blood-retinal barrier is formed by tight junctions between the endothelial cells of the retinal capillaries. This barrier restricts the passage of substances from the circulatory system into the retina.

The outer blood-retinal barrier is formed by tight junctions between the retinal pigment epithelial cells. These cells are located at the back of the eye and are responsible for transporting nutrients from the choroid to the photoreceptor cells of the retina.

Function

The primary function of the blood-retinal barrier is to maintain the homeostasis of the retinal environment. It does this by regulating the exchange of substances between the retina and the blood. This is crucial for the proper functioning of the photoreceptor cells, which are highly sensitive to changes in their environment.

The blood-retinal barrier also protects the retina from potentially harmful substances in the blood. This includes toxins, pathogens, and immune cells, which could damage the retina if they were allowed to enter.

Clinical significance

Disruption of the blood-retinal barrier is a feature of several eye diseases, including diabetic retinopathy, age-related macular degeneration, and retinal vein occlusion. These conditions can lead to vision loss and are major causes of blindness worldwide.

In diabetic retinopathy, high blood sugar levels can damage the blood vessels in the retina, leading to leakage of fluid into the retinal tissue. This can cause swelling and inflammation, which can damage the photoreceptor cells and lead to vision loss.

In age-related macular degeneration, the blood-retinal barrier can become leaky, allowing drusen (deposits of fatty proteins) to accumulate in the retina. This can damage the photoreceptor cells and lead to vision loss.

In retinal vein occlusion, a blood clot in the retinal vein can cause a buildup of fluid in the retina, leading to swelling and damage to the photoreceptor cells.

See also

• Blood–brain barrier
• Retina
• Eye diseases