Significant reduction of the panretinal oxygenation response after 28% supplemental oxygen recovery in experimental ROP

Abstract

Purpose: To test the hypothesis that after supplemental oxygen recovery (SOR) in the newborn rat model of retinopathy of prematurity (ROP) the preretinal neovascular (NV) incidence and severity are decreased and the panretinal oxygenation ability is improved.

Methods: Newborn rats were first raised in either room air (controls) or variable oxygen (50%/10%) for 14 days. The experimental rats were recovered during the next 6 days (until day 20) in either room air (21% O2) or supplemental oxygen (28%). All groups were then exposed to room air for an additional 6 days (until day 26). On day 20, magnetic resonance imaging (MRI) was used to determine the panretinal oxygenation response (deltaPO2, mm Hg) to a carbogen (95% O2/5% CO2) inhalation challenge. On days 20 and 26, the retinas from a different subset of control, room air-recovered, or SOR-recovered animals were analyzed using ADPase stained or fluorescein-labeled dextran infused retinal flatmounts.

Results: On day 20, the panretinal deltaPO2 of the room air-recovered group (125 +/- 5 mm Hg, mean +/- SEM, n = 12) was significantly (P < 0.05) lower than that of the control group (179 +/- 6 mm Hg, n = 11). The panretinal deltaPO2 value for the SOR group (87 +/- 5 mm Hg, n = 7) was significantly (P < 0.05) lower than both the room air-recovered group and the control group. The NV incidence and severity were significantly reduced (P < 0.05) in the SOR animals compared with the room air-recovered animals. In contrast, on day 26 (after 6 days in room air), the NV incidence was statistically (P < 0.05) greater in the animals that had been exposed to SOR compared with room air-recovered animals.

Conclusions: After 28% SOR, the expected decrease in NV incidence and severity occurred but with an unexpected decrease in panretinal oxygenation ability. The present data strongly support an association between subnormal panretinal oxygenation ability and increased NV risk in the newborn rat ROP model. MRI appears to be a powerful new approach for quantitatively and noninvasively measuring retinal oxygenation and may be applicable to study other ischemic or ischemia-related retinopathies in addition to ROP, such as diabetic retinopathy, sickle cell retinopathy, macular degeneration, and glaucoma.