Graded contribution of retinal maturation to the development of oxygen-induced retinopathy in rats

PURPOSE. Newborn rats exposed to hyperoxia during the first days of life ha ve been shown to exhibit not only vasculopathy but also permanent changes i n the structure and function of the retina. Given that the rat retina is im mature at birth and that the maturation process continues until the opening of the eyes at 14 days of life, this study was conducted to investigate th e susceptibility of the retina to oxygen toxicity as a function of the degr ee of retinal maturity reached at the time of oxygen exposure. METHODS. Newborn rats were exposed to hyperoxia during selected postnatal d ay intervals. Scotopic electroretinograms were recorded at 30 and 60 days o f age, and retinal histology was obtained at the end of the study. RESULTS. There was a strong correlation between the duration of the hyperox ic event and the structural and functional consequences in the retina. Howe ver, the repercussions were significantly more profound when the exposure t o oxygen occurred within the second week of life (6-14 days), com pared wit h earlier (0-6 days) or later periods (14-28 days). CONCLUSIONS. The results strongly suggest that the structural and functiona l retinal changes secondary to postnatal hyperoxia are not only the direct consequence of exposure to high levels of oxygen (i.e., free radicals), but also are determined by the level of retinal maturity reached at the time o f oxygen exposure. The results also indicate that the structural anomalies precede the functional impairments.