Comparison of Angle Kappa Measurements: Repeatability of Sirius, Keratron, and Pentacam and Agreement With Amaris 750S.

Abstract

Purpose: To evaluate the repeatability of angle kappa measurements obtained from the Pentacam (Oculus Optikgeräte GmbH), Sirius (Costruzione Strumenti Oftalmici), and Keratron Scout (BVI), and to assess the agreement with those obtained from the Amaris 750S (SCHWIND eye-tech-solutions).

Methods: This study included 110 patients scheduled to undergo transepithelial photorefractive keratectomy or femtosecond laser-assisted laser in situ keratomileusis. Before surgery, each patient underwent angle kappa measurement using three instruments: Pentacam, Sirius, and Keratron. Prior to corneal ablation with the excimer laser during surgery, the angle kappa was measured again using an Amaris 750S. Within-subject standard deviation, test-retest repeatability, within-subject coefficient of variation, and intraclass correlation coefficient (ICC) were calculated to assess the repeatability of the angle kappa measurements using the three instruments before surgery. A Bland-Altman plot was used to evaluate the agreement between these three instruments and the Amaris 750S to measure the angle kappa.

Results: For the kappa offsets measured by Sirius, Keratron, and Pentacam, the ICC values were 0.948, 0.950, and 0.931, respectively. For the measurement of the kappa axis using the three instruments, the ICC values were 0.996, 0.997, and 0.994, respectively. The 95% limits of agreement (LoA) of kappa offset between Keratron and Amaris 750S was from -0.15 to +0.09 mm, which was the narrowest among the three instruments compared with the Amaris 750S, and the narrowest 95% LoA of kappa axial was also between the Keratron and Amaris 750S.

Conclusions: The results measured before Keratron, whether kappa offset or kappa axial, were relatively consistent with those measured intraoperatively using the Amaris 750S. [J Refract Surg. 2025;41(2):e213-e219.].