Effects of vitamin C on hyperoxia-induced reduction of retinal blood flow

Objective: Breathing of 100% oxygen causes vasoconstriction in retinal vessels paralleled by a decrease in blood flow. The mechanism underlying this effect is still unclear, but may be related to the increased generation of reactive oxygen species during hyperoxia. Thus, the purpose of the present study was to investigate whether vitamin C, an agent with strong antioxidative properties, modifies the retinal vasoconstrictor response to hyperoxia. Methods: A randomized, double-masked, placebo controlled, two-way crossover study was performed in 12 healthy young volunteers. 100% oxygen was administered via a breathing mask for 12 min. Retinal blood flow was measured before and during oxygen breathing in the presence of either ascorbic acid (3 g) or placebo on two different study days. Retinal blood flow was determined based on measurement of retinal vessel diameters and red blood cell velocity. Results: Breathing of 100% oxygen induced a pronounced reduction of retinal arterial (- 7.6% ± 6.5%) and venous diameters (- 12% ± 6%). Hyperoxia induced vasoconstriction was not altered by co-administration of vitamin C (- 8.6% ± 4.8% in arteries and - 15% ± 7% in veins). Likewise, RBV and retinal blood flow decreased in response to oxygen by - 24% ± 53% and - 38% ± 42%. Again, the reduction of retinal hemodynamic parameters was not altered by co-administration of vitamin C. Conclusions: Oxygen induced blood flow response in the human retina is not altered by a single dose of vitamin C in healthy, young subjects. Whether this indicates that ROS are not involved in hyperoxia induced vasoconstriction of retinal vessels or is related to other factors has yet to be determined.