Comparison of reliability and repeatability of corneal curvature assessment with six keratometers

Background Keratometric methodology varies between instruments and the differences may have a clinical impact. We investigated the agreement and reproducibility of six keratometers. Methods Keratometry was performed on 100 subjects at two separate sessions with IOLMaster 500, Pentacam, OPD scanner, Medmont E300, Javal-Schiotz and TMS-5. A second observer assessed 30 subjects to determine inter-observer variability. A single individual was assessed on 10 separate sessions to determine intra-observer variability. Data were analysed using coefficient of variation (CV) and intra-class correlation coefficient (ICCC) for intra-observer variation. Inter-observer concordance was evaluated by the ICCC. Bland-Altman plots, Pearson's correlation coefficient and repeated measures analysis of variance were used to assess agreement of data produced by the instruments. Results OPD scanner and Javal-Schiotz mean spherical equivalent (MSE) results were systematically different (p < 0.001) from other instruments (flatter and steeper, respectively). J(0)/J(45) were similar for all instruments (p < 0.05). Bland-Altman comparison plots indicated that Pentacam and IOLMaster demonstrated greatest level of agreement (ICC results MSE = 0.992, J(0) = 0.934 and J(45) = 0.890). Agreement (ICC) between observers for MSE ranged from 0.955 to 0.995 for all instruments; lower levels of agreement were found for J(0)/J(45) (0.289 to 0.901). IOLMaster showed greatest correlation and Medmont the lowest. All instruments showed high intra-observer repeatability of MSE (CV 0.1 to 0.3 per cent). The J(0)/J(45) readings showed greater variability (CV range 8.8 to 57.6 per cent). Conclusion When considering MSE alone IOLMaster, Pentacam, OPD scan and Medmont may be considered interchangeable; however, assessment of astigmatism shows greater variability between instruments, sessions and observers.