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.
[1] It consists of non-fenestrated capillaries of the retinal circulation and tight-junctions between retinal epithelial cells preventing passage of large molecules from choriocapillaris into the retina.
This physiological barrier comprises a single layer of non-fenestrated endothelial cells, which have tight junctions.
These junctions are impervious to tracer, so many substances can affect the metabolism of the eyeball.
The retinal pigment epithelium maintains the outer blood–retinal barrier.