ERRORS IN THE DIAGNOSIS OF VISUAL-FIELD PROGRESSION IN NORMAL-TENSIONGLAUCOMA

Background: Despite strictly defined criteria for visual field progres sion in the ongoing Normal-tension Glaucoma Study, the authors noted a surprisingly large number of patients reaching the endpoint. Traditio nal methods could not be used to check the diagnostic accuracy of thei r criteria, because no ''gold standard'' was established for distingui shing true change from physiologic long-term fluctuation. Methods: The authors developed a statistical method based on the results of duplic ate tests for progression in their subjects. This method allowed the a uthors to assess the sensitivity, specificity, and predictive values o f their diagnostic criterion. It also estimated the true incidence of progression and provided standard errors for the estimates. Results: T he 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 repeati ng the entire sequence of duplicate testing once more, the authors hav e successfully reduced the rate of false calls to 2%. Conclusion: Accu racy in recognizing progression is improved by not accepting small cha nges as evidence of progression and by confirming the findings on repe at testing.