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W. J. Feuer, M. Durbin; Performance of Confirmation as a Strategy to Retain Acceptable Specificity and Sensitivity When Monitoring Glaucoma Over Multiple Visits. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2250.
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Statistical methods to detect reduction in RNFL thickness resulting from glaucomatous progression may suffer from reduced specificity due to alpha error inflation upon repeat testing over long follow-up. The purpose of this study is to evaluate the performance of and compare two strategies for assessing progression: linear regression and confirmed change from baseline.
Data representing 15 semi-annual visits was generated (n=10,000) from a random normal distribution with variability based on that reported for the Average RNFL thickness measurement of the Cirrus HD-OCTTM. In addition, a slow progressive thinning (1.4 µm per year) was applied on top of this to simulate a population of progressors. The simulated, accumulating data was fit with linear regression at each visit, starting with visit 4, until statistical significance (p<0.05) occurred or the 15th visit was reached. Additionally, at each visit, a confirmed change from baseline analysis was performed between the two most recent visits and the two baseline visits (4 separate comparisons). A comparison was considered statistically significant if it exceeded the 95% confidence limits on the difference between two Cirrus average thickness measurements based on an in-house reproducibility study. If three of four comparisons met this criterion, then change from baseline was confirmed. This procedure was similarly repeated for each visit until a change was confirmed or the 15th visit was reached. Sensitivity and specificity of two methods was evaluated.
The figures display how sensitivity and specificity change upon repeat testing for each method.
Compared to linear regression, the confirmed change from baseline strategy keeps specificity high across multiple visits. Sensitivity is reduced with confirmed change, but improves with additional visits.
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