Comparison of corneal curvature and astigmatism measurements in myopia using Sirius Anterior Segment Analysis System and TMS-4 topographer

Objective To explore the repeatability of corneal curvature and astigmatism measurements using Sirius system and the agreement with the TMS-4 conventional topographer in myopia. Methods A prospective control study of 125 patients(125eyes) with myopia before laser vision correction surgery were selected. Measurements of corneal flat keratometry(Kf), steep keratometry(Ks), mean keratometry(Km), corneal astigmatism and axis were taken firstly using Sirius anterior segment analysis system three times to assess the repeatability of the device. The best quality of imagein three acquisitions measured by TMS-4 topographer was chosen for analyzing subsequently. Paired samples t-test and Pearson linear correlation were used for statistical analysis. And a Bland-Altman analysis was used to evaluate the consistency of the two methods of measurement. Results Corneal Kf, Ks, Km, corneal astigmatism and axis measured by Sirius showed high intraobserver repeatability, with all ICC and CoA more than 0.90. Corneal Kf, Km, and astigmatism differences were 0.11±0.14 D, 0.05±0.13 D and-0.12±0.19 D, which were statistically significant, respectively. There were 4.80%,5.60%,5.60%, 5.60% and 5.60% points exceeded 95% LoA of-0.17 to 0.38 D,-0.36 to 0.33 D,-0.20 to0.30 D,-0.50 to 0.26 D and-17.61 to 21.37 degrees for corneal Kf, Ks, Km, astigmatism and axis, respectively. Conclusions Sirius show high repeatability in measurement of corneal curvature and astigmatism, the measurement agreement between Sirius and TMS-4 topographer is not good. Key words: Sirius; TMS-4; Topographer; Keratometry; Astigmatism; Agreement