Aphotographic method for measuring the mean retinal circulation time using fluorescein.

A method is described for measuring mean retinal circulation time in man from serial fundus photographs after injecting fluorescein into a peripheral vein. From densitometric measurements on the photographic images of the retinal vessels an estimate is made of the relative concentration of fluorescein in arterial and venous retinal blood at the time of each picture, and arterial and venous time—concentration curves are constructed. From these curves mean avterial and venous retinal circulation times are calculated by conventional formulas. The mean retinal circulation time is the difference between venous and arterial times. In 29 normal males this averaged 4.7 ±1.1 seconds. The retinal circulation time was prolonged by inhaling 100 per cent oxygen and by sublingual administration of nitroglycerine. It was shortened by inhaling 7 per cent carbon dioxide. By combining measurements of mean retinal circulation time with estimates of change in retinal arteriovenous oxygen difference and change in the diameter of retinal vessels in response to various stimuli, it is possible to estimate relative changes in retinal blood flow and in the rate of oxygen delivery from the retinal vascular system.