title: Progression of type 2 to type 1 retinopathy of prematurity in the Early Treatment for Retinopathy of Prematurity Study.
abstract: OBJECTIVE
  To examine the frequency and timing of progression from type 2 to type 1 retinopathy of prematurity (ROP) in the Early Treatment for Retinopathy of Prematurity Study.
  
  
  METHODS
  Infants with prethreshold ROP that was no worse than low risk in 1 or both eyes, based on the RM-ROP2 model, were examined every 2 to 4 days for at least 2 weeks. Using the Early Treatment for Retinopathy of Prematurity Study-defined classification of eyes as having type 1 or type 2 prethreshold ROP, we analyzed the time to conversion from type 2 to type 1. Data were analyzed for 1 randomly selected eye for each child.
  
  
  RESULTS
  Of 294 eyes at first diagnosis of type 2 ROP, 65 (22.1%) progressed to type 1 (mean [SD] interval, 9.0 [6.6] days; median, 7.0 days). Of 217 eyes with type 2 ROP that had an examination in less than 7 days, 25 (11.5%) were diagnosed with type 1 ROP in less than 7 days. Of 200 eyes that continued to have type 2 disease at the first follow-up examination and underwent a subsequent examination, 24 (15.7% of the 153 eyes that had an examination in <7 days) developed type 1 ROP in less than 7 days. The risk of progression from type 2 to type 1 in less than 7 days was greatest between 33 and 36 weeks' postmenstrual age, regardless of zone of retinopathy.
  
  
  CONCLUSIONS
  Type 1 ROP can be identified with weekly examinations in most eyes with initial diagnosis of type 2 ROP; a small subset progresses to type 1 in less than 7 days.
  
  
  BACKGROUND
  clinicaltrials.gov Identifier: NCT00027222.
authors.affiliation: Department of Ophthalmology, University of Minnesota, Minneapolis, USA. spchris@bu.edu
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Christiansen
authors.forename: Velma
authors.initials: V
authors.lastname: Dobson
authors.forename: Graham E
authors.initials: GE
authors.lastname: Quinn
authors.forename: William V
authors.initials: WV
authors.lastname: Good
authors.forename: Betty
authors.initials: B
authors.lastname: Tung
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Hardy
authors.forename: John D
authors.initials: JD
authors.lastname: Baker
authors.forename: Robert O
authors.initials: RO
authors.lastname: Hoffman
authors.forename: James D
authors.initials: JD
authors.lastname: Reynolds
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Rychwalski
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Shapiro
mesh_terms: D018450:Disease Progression; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D012178:Retinopathy of Prematurity / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology*; D013997:Time Factors; D015351:Vision Screening / Q000379:methods