Regulation of retinal oxygen metabolism in humans during graded hypoxia.

ments indicate that the inner retina keeps its oxygen extraction constant despite systemic hypoxia. For the human retina no such data exist. In the present study we hypothesized that systemic hypoxia does not alter inner retinal oxygen extraction. To test this hypothesis we included 30 healthy male and female subjects aged between 18 and 35 years. All subjects were studied at baseline and during breathing 12% O2 in 88 % N2 as well as breathing 15 % O2 in 85 % N2. Oxygen saturation in a retinal artery (SO2art) and an adjacent retinal vein (SO2vein) were measured using spectroscopic fundus reflectometry. Measurements of retinal venous blood velocity using bidirectional laser Doppler velocimetry and retinal venous diameters using a Retinal Vessel Analyzer (RVA) were combined to calculate retinal blood flow. Oxygen and carbon dioxide partial pressure were mea-sured from earlobe arterialized capillary blood. Retinal blood flow was increased by 43.0 23.2 % (P 0.001) and 30.0 20.9 % (P 0.001) during 12 % and 15 % O2 breathing, respectively. SO2art as well as SO2vein decreased during both 12 % O2 breathing (SO2art: 11.