The mean preretinal vitreous oxygen tensions over vascular retina at P14 (before the appearance of NV) was 28 ± 5 mm Hg (
n = 7, average distance ratio 0.47; range, 0.3–0.7) and at P20 (during the appearance of NV) was 26 ± 4 mm Hg (
n = 8, mean distance ratio 0.52; range, 0.3–0.7;
Fig. 2 ). These oxygen tensions were not statistically different from the P
o 2s measured over vascularized retina in P1 to P10 control rats (27 ± 2 mm Hg, see above) or in P14, P20, and adult vascularized rat retinas (24 ± 2 mm Hg). However, because of the droplet and vitreous space sizes, it was not possible to obtain oxygen tension measurements at the border of vascular and avascular retina. The data scatter in the relatively small number of P14 ROP data points probably prevented linear regression analysis from achieving significance (
r = −0.73,
P = 0.06). Nonetheless, in the P14 ROP animals, a significant correlation (
r = −0.82,
P = 0.02) was found between the retinal P
o 2 and ratio of droplet distance from the optic nerve head to extent of vascularized retina
(Fig. 3) . No such correlation was found in P14 control rat pups (
r = −0.77,
P = 0.07; distance ratio, 0.39; range, 0.08–0.7), P20 control rats (
r = −0.41,
P = 0.21; distance ratio, 0.54; range, 0.08–0.8), and in P20 ROP newborns (
r = 0.17,
P = 0.69; distance ratio, 0.52; range, 0.3–0.7; data not shown).