Central corneal thickness and anterior chamber depth measurement by Sirius (R) Scheimpflug tomography and ultrasound

Background: The purpose of this study was to compare the accuracy of the new Sirius (R) Scheimpflug anterior segment examination device for measurement of central corneal thickness (CCT) and anterior chamber depth (ACD) with that of CCT measurements obtained by ultrasound pachymetry and ACD measurements obtained by ultrasound biometry, respectively. Methods: CCT and ACD was measured in 50 right eyes from 50 healthy subjects using a Sirius Scheimpflug camera, SP100 ultrasound pachymetry, and US800 ultrasound biometry. Results: CCT measured with the Sirius was 546 +/- 39 mu m and 541 +/- 35 mu m with SP100 ultrasound pachymetry (P = 0.003). The difference was statistically significant (mean difference 4.68 +/- 10.5 mu m; limits of agreement -15.8 to 25.20 mu m). ACD measured with the Sirius was 2.96 +/- 0.3 mm compared with 3.36 +/- 0.29 mm using US800 ultrasound biometry (P < 0.001). The difference was statistically significant (mean difference -0.40 +/- 0.16 mm; limits of agreement -0.72 to 0.07 mm). When the ACD values obtained using ultrasound biometry were corrected according to the values for CCT measured by ultrasound, the agreement increased significantly between both technologies for ACD measurements (mean difference 0.15 +/- 0.16 mm; limits of agreement -0.16 to 0.45 mm). Conclusion: CCT and ACD measured by Sirius and ultrasound methods showing good agreement between repeated measurements obtained in the same subjects (repeatability) with either instrument. However, CCT and ACD values, even after correcting ultrasound ACD by subtracting the CCT value obtained with either technology should not be used interchangeably.