Effects of oxygen and carbon dioxide on human retinal circulation: an investigation using blue field simulation and scanning laser ophthalmoscopy

To investigate the quantitative response of retinal circulation in normal human eyes to oxygen and carbon dioxide provocation and to gain more information about retinal mean transit time (MTT).Healthy subjects were studied while breathing: room air (O2 baseline); pure O2; room air (CO2 baseline), and CO2 in room air. The CO2 level was brought to 30% above individual baseline level. During each gas exposure, blue field simulation was used to estimate the velocity of macular leucocytes and fluorescein angiography was used to determine MTT, arteriovenous passage time (AVP) and vessel diameters.Breathing pure O2 caused a reduction in macular leucocyte velocity of about 13%, a non-significant change in MTT and AVP from baseline, and a 10% reduction in the diameter of temporal retinal arteries and veins. Breathing CO2 caused an increase in macular leucocyte velocity of 21%, a non-significant change in MTT and AVP, and no change in retinal vascular diameters.Both O2 and CO2 had the expected effects on retinal blood flow, as judged by leucocyte velocity in the macular capillaries, but little effect on retinal MTT, indicating concomitant changes in flow and retinal vascular volume. Measuring the diameter of retinal vessels before and during pure O2 breathing is a simple and effective way of determining the reactivity of retinal vessels.