Figure 1.

Schematic diagram of the ocular structure with various ocular barriers. The ocular barriers in the anterior segment area (I) tear film and corneal epithelium, and (II) aqueous humor. The ocular barriers in the posterior segment are (III) sclera, (IV) choroid, and (V) vitreous humor. There are two BRBs. The blood–aqueous barrier in the anterior segment, a part composed of the non-pigmented ciliary epithelial cells and iris capillaries endothelial cells. The BRB, a tight-junction between non-fenestrated capillaries of the retinal blood circulation and retinal pigment epithelial cells in the posterior segment of the eye.