Comparison of the Orbscan II topographer and the iTrace aberrometer for the measurements of keratometry and corneal diameter in myopic patients

BACKGROUND The purpose of this study was to compare corneal power and horizontal corneal diameter (white-to-white [WTW] distance) readings obtained by the Orbscan II topographer and the iTrace aberrometer. METHODS Keratometry readings in the flat (Kf) and steep (Ks) meridians and WTW distance were measured with the Orbscan II and iTrace systems in 100 myopic patients. Statistical evaluation was performed using the paired t test, Pearson correlation, and Bland-Altman analysis for comparison of measurement techniques. RESULTS The mean keratometry values with the Orbscan II and iTrace were 43.16 ± 1.44 and 42.64 ± 1.43 diopter (D), respectively (P < 0.0001). The mean WTW distance measurements with the Orbscan II and iTrace were 11.57 ± 0.34 and 11.33 ± 0.36 mm, respectively (P < 0.0001). For the measurement of corneal power, the 95 % limits of agreement (LoA) between the Orbscan II and iTrace were - 0.21 to 1.21 D for the flat meridian and - 0.15 to 1.25 D for the steep meridian. For the measurement of WTW distance, the range of the 95 % LoA between the two devices was 0.47 mm. CONCLUSIONS For some clinical applications, the keratometry and WTW distance measurements obtained by the Orbscan II topographer and the iTrace aberrometer differed greatly and therefore were not interchangeable. TRIAL REGISTRATION Clinical trials number: ChiCTR-OCS-14005077 (August 2nd, 2014).