Symmetry of Disease in Retinopathy of Prematurity in the Postnatal Growth and Retinopathy of Prematurity (G-ROP) Study

Purpose To determine the symmetry of retinopathy of prematurity (ROP) between fellow eyes in a broad-risk cohort. Methods A retrospective cohort study, the Postnatal Growth and ROP (G-ROP) Study, of 7483 infants undergoing ROP examinations conducted at 29 hospitals in the United States and Canada from 2006 to 2012. The main outcomes were the symmetry for the highest stage and the most severe type (1, 2, not 1 or 2, no ROP) of ROP and disease course of the fellow eye when only one eye developed type 1. Results 93% of infants had eyes symmetric for the highest stage and 94% for type. Among 459 infants who developed type 1, 379 (82.6%) did so in both eyes simultaneously and were treated bilaterally; 44 (10%) were treated for type 1 in one eye and type 2 in the fellow eye; and 36 (8%) were treated unilaterally initially, of which 6 fellow eyes developed type 1 and were treated (4 within 2 weeks, all within 4 weeks); 5 developed type 2 and regressed; and 25 developed ROP less than type 1 or 2, which was treated in 13 cases and regressed spontaneously in 12 cases. Conclusions ROP was highly symmetric between eyes with respect to the presence and severity of disease in a large, broad-risk cohort representative of infants undergoing ROP screening. When type 1 develops in one eye and type 2 in the fellow eye, the risk of progression to type 1 in the fellow eye appears very low if it has not occurred within 4 weeks.