Placido disk-based topography versus high-resolution rotating Scheimpflug camera for corneal power measurements in keratoconic and post-LASIK eyes:reliability and agreement

摘要

AIM:To compare the repeatability/reproducibility of measurement by high-resolution Placido disk-based topography with that of a high-resolution rotating Scheimpflug camera and assess the agreement between the two instruments in measuring corneal power in eyes with keratoconus and post-laser in situ keratomileusis(LASIK). METHODS:One eye each of 36 keratoconic patients and 20 subjects who had undergone LASIK was included in this prospective observational study. Two independent examiners worked in a random order to take three measurements of each eye with both instruments. Four parameters were measured on the anterior cornea:steep keratometry(Ks),flat keratometry(Kf),mean keratometry(Km),and astigmatism(Ks-Kf). Intra-examiner repeatability and inter-examiner reproducibility were evaluated by calculating the within-subject standard deviation(Sw)the coefficient of repeatability(R),the coefficient of variation(Co V),and the intraclass correlation coefficient(ICC). Agreement between instruments was tested with the BlandAltman method by calculating the 95% limits of agreement(95% Lo A).RESULTS:In keratoconic eyes,the intra-examiner and inter-examiner ICC were >0.95. As compared with measurement by high-resolution Placido disk-based topography,the intra-examiner R of the high-resolution rotating Scheimpflug camera was lower for Kf(0.32 vs 0.88),Ks(0.61 vs 0.88),and Km(0.32 vs 0.84)but higher for Ks-Kf(0.70 vs 0.57). Inter-examiner R values were lower for all parameters measured using the high-resolution rotating Scheimpflug camera. The 95% Lo A were-1.28 to +0.55 for Kf,-1.36 to +0.99 for Ks,-1.08 to +0.50 for Km,and-1.11 to +1.48 for Ks-Kf. In the post-LASIK eyes,the intra-examiner andinter-examiner ICC were >0.87 for all parameters. The intra-examiner and inter-examiner R were lower for all parameters measured using the high-resolution rotating Scheimpflug camera. The intra-examiner R was 0.17 vs 0.88 for Kf,0.21 vs 0.88 for Ks,0.17 vs 0.86 for Km,and 0.28 vs 0.33 for Ks-Kf. The inter-examiner R was 0.09 vs 0.64 for Kf,0.15 vs 0.56 for Ks,0.09 vs 0.59 for Km,and 0.18 vs 0.23 for Ks-Kf. The 95% Lo A were-0.54 to +0.58 for Kf,-0.51 to +0.53 for Ks and Km,and-0.28 to +0.27 for Ks-Kf. CONCLUSION:As compared with Placido disk-based topography,the high-resolution rotating Scheimpflug camera provides more repeatable and reproducible measurements of Ks,Kf and Ks in keratoconic and post-LASIK eyes. Agreement between instruments is fair in keratoconus and very good in post-LASIK eyes.