Blood–ocular barrier

Physical barrier between the local blood vessels and most parts of the eye itself

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]

References

^ Peiffer, Robert L.; Petersen-Jones, Simon M. (2001). Small animal ophthalmology: a problem-oriented approach. Elsevier Health Sciences. p. 46. ISBN 978-0-7020-2570-9.^{[permanent dead link]}
^ ^a ^b Kramer, Axel; Behrens-Baumann, Wolfgang (2002). Antiseptic prophylaxis and therapy in ocular infections: principles, clinical practice, and infection control. Karger Publishers. p. 72. ISBN 978-3-8055-7316-0.
^ Giguère, Steeve; Prescott, John F.; Desmond Baggot, J. (2006). Antimicrobial therapy in veterinary medicine. Wiley-Blackwell. p. 366. ISBN 978-0-8138-0656-3.
^ Coscas, G.; Cunha-Vaz, J.; Loewenstein, A.; Soubrane, G. (2010). Macular Edema: A Practical Approach. Karger Publishers. p. 59. ISBN 978-3-8055-9434-9.
^ Maggs, David J.; Miller, Paul E.; Ofri, Ron; Slatter, Douglas H. (2008). Slatter's fundamentals of veterinary ophthalmology. Elsevier Health Sciences. p. 455. ISBN 978-0-7216-0561-6.

Anatomy of the globe of the human eye

Fibrous tunic
(outer)

Sclera	Episcleral layer Schlemm's canal Trabecular meshwork
Cornea	Limbus layers Epithelium Bowman's Stroma Dua's layer Descemet's Endothelium

Uvea / vascular
tunic (middle)

Choroid	Capillary lamina of choroid Bruch's membrane Sattler's layer
Ciliary body	Ciliary processes Ciliary muscle Pars plicata Pars plana
Iris	Stroma Pupil Iris dilator muscle Iris sphincter muscle

Retina (inner)

Layers	Inner limiting membrane Nerve fiber layer Ganglion cell layer Inner plexiform layer Inner nuclear layer Outer plexiform layer Outer nuclear layer External limiting membrane Layer of rods and cones Retinal pigment epithelium
Cells	Photoreceptor cells (Cone cell, Rod cell) → (Horizontal cell) → Bipolar cell → (Amacrine cell) → Retina ganglion cell (Midget cell, Parasol cell, Bistratified cell, Giant retina ganglion cells, Photosensitive ganglion cell) → Diencephalon: P cell, M cell, K cell, Muller glia
Other	Macula Perifoveal area Parafoveal area Fovea Foveal avascular zone Foveola Optic disc Optic cup Ora serrata

Anatomical regions
of the eye

Anterior segment	Adnexa (Eyebrow, Eyelid, Conjunctiva, Lacrimal system, Orbit) Fibrous tunic Anterior chamber Aqueous humour Iris Posterior chamber Ciliary body Lens Capsule of lens Zonule of Zinn
Posterior segment	Vitreous chamber Vitreous body Retina Choroid