Principles of fluorescein angiography.

There are two barriers between the blood and retina--one in the retinal circulation at the endothelial cell lining with its tight junctions in the retinal capillaries, and the second involving the choroidal circulation at the zonula occludens between adjacent retinal pigment epithelial cells. Damage to either of these barriers results in a leakage of fluid into or beneath the sensory retina. Serous detachment of the retinal pigment epithelium is a special situation in which both barriers remain intact but fluid accumulates in the space between the detached pigment epithelial cells and Bruch's membrane. It is convenient to analyze the fluorescein angiographic findings in relation to these two barriers, as a large number of retinal disorders affect either the retinal vascular system or the choriocapillaris-Bruch's membrane-pigment epithelium layers.