Retinal hemodynamic effects of carbon dioxide, hyperoxia, and mild hypoxia

Retinal leukocyte velocity and density were estimated using blue-field entoptic imaging techniques in a controlled double-masked study to determine the relative effects of oxygen and carbon dioxide on perimacular hemodynamics in single eyes of ten normal human subjects. Mild hypoxia (inspiration of 16% O2) did not significantly alter leukocyte velocity or density from room-air baseline levels. Supplementing 16% oxygen with 5% CO2 produced a tendency toward increased leukocyte velocity (+23%, P = 0.027) with no apparent effect on leukocyte density. Inspiration of pure oxygen was associated with significant reductions in both retinal leukocyte velocity (-20%, P less than 0.007) and density (-23%, P = 0.013) relative to room-air baseline levels. Supplementation of pure oxygen with 5% CO2 appeared to produce a dramatic change in perimacular hemodynamics, tending to increase leukocyte velocity (+26%, P = 0.018) with a limited density change (-11%, P = 0.049). These findings suggest that inspired 5% CO2 can counteract the profound inhibitory effects of excess oxygen on retinal hemodynamics in the functionally important perimacular capillary bed.