| Description |
Purpose: The main goal of our study was to prove the statistical significant correlation between repeated measurements and test-retest variability TRV expressed with confidence interval CI according to Bland-Altman’s method. Methods: We had 468 measurements. The average value of the first sequence of measurements measured with whole-line method on Snellen chart was -0,043 logMAR (min. 1, max. -0,30, SD 0,25) and of the second sequence of measurements was -0,045 logMAR (min. 1, max. -0,30, SD 0,23). The average value of the first sequence of measurements measured with interpolation method on Snellen chart was -0,018 logMAR (min. 0,98, max. -0,30, SD 0,29) and of the second sequence of measurements was -0,024 logMAR (min. 1, max. -0,80, SD 0,29). The average value of the first sequence of measurements measured with interpolation method on ETDRS chart was -0,0612 logMAR (min. 0,72, max. -0,30, SD 0,21) and of the second sequence of measurements was -0,0610 log MAR (min. 0,8, max. -0,28, SD 0,21). Results: We have proved that all methods do not have statistical significant difference between repeated measurements (Wilcoxon paired test, whole-line method on Snellen chart p = 0,74, interpolation method on Snellen chart p = 0,33 and interpolation method on ETDRS p = 0,95) and they also have statistical significant correlations (Spearman correlation coefficient, whole-line method on Snellen chart r = 0,91, p < 0,0001, interpolation method on Snellen chart r = 0,89, p < 0,0001 and interpolation method on ETDRS chart r = 0,89, p < 0,0001). TRV expressed with CI on 95% statistical significance level according to method of Bland-Altman was with whole-line method on Snellen chart +/-0,11 (i.e. 5 letters), with interpolation method on Snellen chart +/-0,20 (i.e. 10 letters) and with interpolation method on ETDRS +/-0,08 (i.e. 4 letters). Conclusion: Our recommendation based on results of our study is that is not clinically appropriate to convert measured values from Snellen optotype to logMAR and perform interpolation method on Snellen chart.
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