Blood–ocular barrier

The blood–ocular barrier is a barrier created by endothelium of capillaries of the retina and iris, ciliary epithelium and retinal pigment epithelium.^[1] It is a physical barrier between the local blood vessels and most parts of the eye itself, and stops many substances including drugs from traveling across it.^[2] Inflammation can break down this barrier allowing drugs and large molecules to penetrate into the eye.^[3] As the inflammation subsides, this barrier usually returns.

It consists of the following components:

• Blood–aqueous barrier: the ciliary epithelium and capillaries of the iris.^[2] Blood-aqueous barrier is formed by nonpigmented ciliary epithelial cells of the ciliary body and endothelial cells of blood vessels in the iris.
• Blood–retinal barrier: non-fenestrated capillaries of the retinal circulation and tight-junctions between retinal epithelial cells preventing passage of large molecules from choriocapillaries into the retina. Formed by endothelium of retinal vessels and epithelium of retinal pigment. ^[4][5]

See also

• Blood–air barrier – Membrane separating alveolar air from blood in lung capillaries
• Blood–brain barrier – Semipermeable capillary border that allows selective passage of blood constituents into the brain
• Blood–retinal barrier – Part of the blood–ocular barrier that prevents certain substances from entering the retina
• Blood–saliva barrier – Semipermeable biological barrier
• Blood–testis barrier – Physical barrier between the blood vessels and the seminiferous tubules of animal testes
• Blood–thymus barrier – Barrier formed by the continuous blood capillaries in the thymic cortex