Thresholds were measured in 36 subjects with a history of preterm birth (
Table). Gestational age at birth ranged from 24 to 32 weeks (median: 27 weeks) and birthweight from 530 to 2070 g (median: 998 g). Although, on average, those with severe ROP were born earlier and had lower birthweight, there was considerable overlap among the preterm groups. All subjects had serial fundus examinations in the newborn intensive care nursery following a schedule similar to that used in multicenter clinical trials.
12 In the international classification of retinopathy of prematurity (ICROP) classification of active ROP, location of the retinopathy is specified by zone, severity by stage, and extent by clock hours.
13 Retinopathy of prematurity is an active disease at preterm ages and resolves by the early postterm weeks.
14 We categorized each subject based on the results of examinations in the nursery according to maximum severity of acute-phase ROP as severe ROP (
n = 10); mild ROP (
n = 14); or no ROP (
n = 12). Those in the severe category had been treated by laser ablation of avascular peripheral retina. In all severe ROP subjects, the retina was clinically healed; the region of treated retina was peripheral to the 20° site of the test stimuli. The maximum severity was stage 3; three had zone I disease and none had retinal detachment. Those in the mild category had ROP that, by clinical criteria, resolved completely without treatment. Their maximum severity of ROP was stage 1 or 2 in zone II or III.
13 In all 24 participants who had ROP, the disease had been symmetric in the two eyes. Those in the no ROP category had serial examinations and ROP was never detected. The subjects ranged in age from 9 to 17 years (median: 13.5 years) at the time of testing. A total of 11 healthy, term-born control subjects aged 10 to 17 years (median: 12.8 years) also participated.
The study conformed to the tenets of the Declaration of Helsinki and was approved by the Children's Hospital Committee on Clinical Investigation. Written informed consent was obtained from the parents and assent from the children before each session.