Repeatability of Posterior Corneal Surface Measurements and Zernike Polynomials of Two Ocular Biometers With Single and Dual Scheimpflug Cameras in Keratoconus and Healthy Eyes.

Purpose: This study aims to evaluate the repeatability of posterior corneal surface and Zernike polynomial measurements of 2 different ocular biometers and Scheimpflug devices in keratoconus (KC) and healthy eyes.

Methods: This is a prospective, comparative study performed at the Department of Ophthalmology, Goethe-University Frankfurt, Germany. Included were KC and healthy eyes. Two consecutive measurements of 1 eye per patient, taken with Galilei G6 (Ziemer, Switzerland) and Pentacam AXL (Oculus, Germany), were analyzed. Repeatability was evaluated for posterior keratometry (K1, K2 and Km), posterior astigmatism, and the following Zernike polynomials: Defocus, Astigmatism, Coma, Trefoil, Spherical Aberration, and root mean square (RMS) total.

Results: Both devices showed good repeatability for many of the analyzed parameters with several interclass correlation (ICC) values of 0.96 or above. Regarding the Zernike polynomials, ICC values and the narrowness of the 95% limits of agreement varied in between the devices for each polynomial. In addition, the agreement between both devices was reduced for the Zernike analysis. The only comparable polynomials were Spherical Aberration with a high interdevice ICC of 0.955 and RMS total with a lower ICC of 0.591 (both in the KC group).

Conclusions: Regarding the posterior measurements, Pentacam AXL showed higher repeatability in healthy eyes and Galilei G6 in KC eyes. For both devices, the intradevice repeatability was high for most Zernike polynomials. However, the interdevice comparability for Zernike polynomials was reduced to Spherical Aberration and RMS total, with Spherical Aberration showing higher agreement in KC eyes.