Iris arteriolar diameters in hypoxia and hyperoxia: a photographic study in albino guinea pigs

The irides of albino guinea pigs were photographed, and the iris arteriolar diameters were measured with the animal breathing room air, 10% O2/90% N2, or 100% O2. The iris arterioles constrict significantly in hyperoxia and dilate in hypoxia. The average constriction in 100% O2 was 27% +/- 8%, and the average dilatation in 10% oxygen was 34% +/- 20%.