Mice with their dams were exposed to 75% O2 and 25% N2 (premix; Airgas, Inc., St. Louis, MO) from postnatal day (P)7 to P12. Oxygen levels were monitored with an oxygen analyzer (Model D2; Beckman, Irvine, CA). After return to room air, the degree of retinopathy was determined by angiography on P12 and P17. Some animals were used to assess the degree of oxygen-induced retinopathy through histology on P12, P14, P17, P21, and P26. Normoxia control subjects were examined on the same days, and no retinal abnormalities or preretinal nuclei were observed under these conditions. Our study strictly followed the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research.