The purpose of the proposed study is to examine the long-term structural and functional effects of cryotherapy as a treatment for severe retinopathy of prematurity (ROP). In the initial phase of the study, eyes with 5 contiguous or 8 total clock hours of stage 3 plus, in 291 infants with birth weights less than 1251 g, were randomized to receive cryotherapy or not cryotherapy. Follow-up to age 12 months indicated that cryotherapy reduced the incidence of unfavorable structural outcome by ~5.8 percent and the incidence of unfavorable visual acuity outcome by 37.8 percent. Based on the preliminary data, follow- up to age ~2 months during Phase II of the study indicated that cryotherapy reduced the incidence of unfavorable structural outcome by 39.1 percent. As for vision, cryotherapy reduced the incidence of unfavorable resolution acuity outcome by 21.4 percent, and by 19.7 percent when based on measurement of recognition acuity.
