http://repub.eur.nl/res/aut/36035/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/26241/ 1974-12-11T00:00:00Z When considering the many questions that still arise concerning the haemodynamics of the posterior segment of the eye, distinction must be made between the retinal and choroidal vasculature. Although the retinal circulation is still to be investigated more intensively, there exists a fair amount of information on this item. Photographic methods (HICKAM & FRAZER, 1966) make it possible to give fairly accurate estimates of the diameter of the larger retinal arteries and veins and their arteriovenous oxygen differences. The mean circulation time in the retinal vessels can be calculated (BULPITT & DOLLERY, 1971) and so can alterations in this time under influence of a raised intra~ocular pressure (DOLLERY et al., I968). Not so for the circulation in the choroid. Covered by a layer of dense pigment, it is hardly accessible to fluorescein angiographic research. Also cardiogreen, which enables the use of longer wavelength light, which is absorbed to a lesser degree by the pigment epithelium, does not give satisfying information (BROWN & STRONG, 1973). Many research workers could not resist the temptation to tap vortex,; veins in animals (BILL, 1962a; 1962b; BEST et al., 1972; NAKAMURA & GOULSTINE, 1973; SCHLEGEL & LAWRENCE, 1969) to catheterize the long posterior ciliary artery (BILL, 1963a), tO place probes (BILL, 1963b; NIESEL & KONSTAS, 1959), Of to dehydrate the sclera (GREAVES & PERKINS, 1952) in order to measure flow, record pressures or study the behaviour of choroidal vessels under the micro~ scope. Unfortunately all these methods are apt to disturb the physiological conditions of the eye.