title: Screening for amblyopia in preschool children: results of a population-based, randomised controlled trial. ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood.
abstract: BACKGROUND
  The rationale for preschool vision screening programmes has recently been questioned. Evidence about the effects of early treatment is needed, but it is not known how early the target conditions can reliably be detected. In this study, an intensive programme comprising several different screening methods, used at different ages up to 37 months, was compared with the usual practice of visual surveillance and ad hoc referrals.
  
  
  METHODS
  Two groups were randomly selected from children in a population birth cohort study. The control group (n = 1461) received visual surveillance only. The intervention group (n = 2029) was offered in addition a programme of regular visual assessments by orthoptists testing visual acuity, ocular alignment, stereopsis and non-cycloplegic photorefraction.
  
  
  RESULTS
  The intervention group programme yielded more children with amblyopia (1.6% vs. 0.5%, p < 0.01), and was more specific (95% vs. 92%, p < 0.01), than the control programme. The individual components of the intervention programme were compared. The cover test and visual acuity tests were poorly sensitive until the children were 37 months, but were always >99% specific. Photorefraction was more sensitive than acuity testing at all ages below 37 months, with specificity >95% at 31 and 37 months.
  
  
  CONCLUSIONS
  Photorefraction would have detected more children less than 37 months of age with straight-eyed amblyopia than did visual acuity testing, but with more false positives. At 37 months, photorefraction plus a cover test would have been comparable in effectiveness to visual acuity testing plus a cover test.
authors.affiliation: Department of Ophthalmology, University of Bristol, UK. Cathy.Williams@bristol.ac.uk
authors.forename: C
authors.initials: C
authors.lastname: Williams
authors.forename: R A
authors.initials: RA
authors.lastname: Harrad
authors.forename: I
authors.initials: I
authors.lastname: Harvey
authors.forename: J M
authors.initials: JM
authors.lastname: Sparrow
mesh_terms: D000550:Amblyopia / Q000175:diagnosis* / Q000453:epidemiology; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D012030:Refractive Errors / Q000175:diagnosis; D013285:Strabismus / Q000175:diagnosis; D006113:United Kingdom / Q000453:epidemiology; D015351:Vision Screening / Q000379:methods*