Natural course of retinal development in preterm infants without threshold retinopathy.

In a consecutive series, 209 preterm infants with birth weights below 1501 g or a gestational age of < or = 32 weeks were observed. Stage 3 retinopathy of prematurity (ROP) developed in 48 infants (23%) of between 32 and 46 weeks postconceptional age (PCA; mean, 37 weeks). Stage 3 ROP was not seen before 6 weeks after birth. Threshold ROP was seen and treated at between 34 and 42 weeks PCA (mean, 38 weeks PCA; n = 22, 10.5%). A subgroup of 126 untreated infants were followed until complete retinal vascularisation. At estimated term, 38.7% of eyes with vessels ending in zone 3 at the first examination showed complete vascularisation as compared with 17.6% of eyes with vessels ending in peripheral zone 2 and none of those with vessels ending in central zone 2. Occurrence of ROP delayed retinal development. At estimated term, no eye with any stage of ROP showed complete vascularisation as compared with 35.4% of eyes without ROP. Regression of stage 3 ROP below threshold started in all cases before 56 weeks PCA.