title: Errors in the diagnosis of visual field progression in normal-tension glaucoma.
abstract: BACKGROUND
  Despite strictly defined criteria for visual field progression in the ongoing Normal-tension Glaucoma Study, the authors noted a surprisingly large number of patients reaching the endpoint. Traditional methods could not be used to check the diagnostic accuracy of their criteria, because no "gold standard" was established for distinguishing true change from physiologic long-term fluctuation.
  
  
  METHODS
  The authors developed a statistical method based on the results of duplicate tests for progression in their subjects. This method allowed the authors to assess the sensitivity, specificity, and predictive values of their diagnostic criterion. It also estimated the true incidence of progression and provided standard errors for the estimates.
  
  
  RESULTS
  The authors found that their original strict criteria for progression, based on duplicate testing, produced false calls of progression 57% of the time. By raising the requirement for deterioration and by repeating the entire sequence of duplicate testing once more, the authors have successfully reduced the rate of false calls to 2%.
  
  
  CONCLUSIONS
  Accuracy in recognizing progression is improved by not accepting small changes as evidence of progression and by confirming the findings on repeat testing.
authors.affiliation: Department of Medicine, University of British Columbia, Vancouver, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Schulzer
mesh_terms: D003951:Diagnostic Errors; D005901:Glaucoma / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D007429:Intraocular Pressure; D008433:Mathematics; D008954:Models, Biological; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014786:Vision Disorders / Q000175:diagnosis* / Q000503:physiopathology; D058609:Visual Field Tests / Q000379:methods; D014794:Visual Fields / Q000502:physiology