Objectives. To estimate the incidence of retinopathy of prematurity (ROP) in the Early Treatment for Retinopathy of Prematurity (ETROP) Study and compare these results with those reported in the Cryotherapy for Retinopathy of Prematurity (CRYO-ROP) Study.

Methods. The ETROP Study, as part of its protocol, screened 6998 infants at 26 centers throughout the United States. Serial eye examinations were conducted for infants born weighing <1251 g, making it possible to estimate the frequency of ROP in different birth weight and gestational age categories. ROP was categorized according to the International Classification for ROP.

Results. The incidence of any ROP was 68% among infants of <1251 g. The findings were compared with those for infants born in 1986 and 1987 in the CRYO-ROP Study. The overall incidences of ROP were similar in the 2 studies, but there was more zone I ROP in the ETROP Study. Among infants with ROP, more-severe ROP (prethreshold) occurred for 36.9% of infants in the ETROP Study and 27.1% of infants in the CRYO-ROP Study. The gestational age of onset of ROP of different severities has changed very little since the CRYO-ROP Study was conducted.

Conclusions. ROP remains a common important problem among infants with birth weights of <1251 g. The incidence of ROP, time of onset, rate of progression, and time of onset of prethreshold disease have changed little since the CRYO-ROP natural-history study.

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