Hydrostatic pressures within the eye (author's transl)]

In the eye all membranes are more or less under tension, as elsewhere in the body. Hence the hydrostatic pressure in the choroid is less than in the retina. The available pressure difference within the bloodvessels would be less for the retina than for the choroid, if the arteries to the retina did not have a much larger bore than those to the choroid. Hence the bloodstream for the retina is slower and fluorescein appears later in the retina than in the choroid. There is a flow of tissue fluid from the choroid to the retina. It is absorbed by the retinal vessels. The larger the flow, the larger are the retinal veins, till retinal oedema occurs. Then the tissue pressure within the retina rises sharply and the capillaries become strangulated. But a few capillaries remain open and are blown up to arterio-venular shunts. Micro-aneurysmata arise as abortive vessel sprouts. It is plausible that lightcoagulation sticks the lamellae of Bruch's membrane together, to the extent that the development of oedema is arrested.