In diabetic retinopathy, a low resistance of flow between choroid and retina is found which goes with an increased intake of tissue fluid into the retinal vessels and the appearance of retinal oedema. Light coagulation destroys the choriocapillaris which does not regenerate. As less fluid becomes available to be sucked up by the retinal vessels, the oedema will now disappear and consequently, the retinopathy subsides.