Consistency in measuring corneal curvature with Sirius corneal topography and a keratometer

Objective To explore the differences and agreements between Sirius corneal topography and a keratometer in the measurement of corneal curvature before laser in situ keratomileusis (LASIK) in patients with myopia.Methods This was a prospective control study.One hundred and seventy eyes of 85 patients with myopia were selected at The People's Hospital of Shaoxing.Measurements of corneal curvature were taken with both Sirius corneal topography and a keratometer.A paired samples t-test and Pearson linear correlation were used for statistical analysis,and a BlandAltman analysis was used to evaluate the consistency of the two methods of measurement.Results The corneal curvature K1 values measured by Sirius corneal topography and a keratometer were 42.41±1.25 D and 42.33±1.28 D,K2 values were 43.36±1.38 D and 43.56±1.38 D,and (K1+K2)/2 values were 42.88±1.28 D and 42.92±1.29 D,respectively,indicating significant differences (t1=5.241,P＜0.01; t2=-9.936,P＜0.01; taverage=-3.021,P＜0.01) and significant linear correlations between K1 and K2 (r1=0.989,P＜0.01 ;r2=0.981,P＜0.01; raverage=0.990,P＜0.01).The differences between Sirius corneal topography and keratometry measurements of corneal curvature for K1 and K2 values and the differences in average corneal curvature (K1+K2)/2 were 0.08 D,-0.20 D and-0.04 D,respectively.The differences between standard deviations were 0.1897 D,0.2644 D and 0.1790 D and the 95％ limits of agreement were (0.45 D,-0.30 D),(0.32 D,-0.72 D) and (0.31 D,-0.39 D).There were 2.4％(4/170),3.5(6/170) and 4.7％(8/170) points for the 95％ limits of agreement,and consistency within