Objective: To report the timing of involution of acute retinopathy of prematurity (ROP). Design: An analysis of prospective retinal observational data recorded at infants' eye examinations. Participants: Infants from the Multicenter Trial of Cryotherapy for Retinopathy of Prematurity (CRYO-ROP) had birth weights less than 1251 g and served as subjects. The study population included 766 children who were examined in 5 of the 23 study centers and who developed at least 1 clock hour of acute ROP, stages 1 through 3. One eye from each patient was randomly chosen for analysis. Main Outcome Measures: Investigators documented the location, extent, and severity of ROP during serial retinal examinations. The onset of the ROP's involution was determined from a review of these data, applying a set of predetermined criteria. Results: Acute-phase ROP began to involute at a mean of 38.6 weeks postmenstrual age. In 90% of patients, the ROP began to involute before 44 weeks of postmenstrual age. Acute ROP that demonstrated involution by moving from zone II to zone III was associated with an unfavorable outcome in 2 (1%) of 200 cases. Retinopathy of prematurity that was present only in zone III during a child's serial retinal examinations was never associated with the development of a partial or total retinal detachment. Conclusions: The onset of involution of acute retinopathy of prematurity correlates better with postmenstrual rather than with chronological age. This is reminiscent of the reported similar correlation of postmenstrual age to the time of onset of prethreshold and threshold ROP. Zone III ROP was nearly always associated with a favorable outcome.
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