Agreement between swept-source optical biometry and Scheimpflug-based tomography in eyes with previous myopic refractive surgery

PURPOSE: The purpose of the study is to evaluate the comparability of corneal power measurements, anterior chamber depth (ACD), and white-to-white (WTW) distance between a high-resolution Scheimpflug-based tomography (Pentacam HR; Oculus GmbH, Wetzlar, Germany) and a swept-source optical biometry, IOL Master 700; Carl Zeiss Meditec AG, Jena, Germany) in patients having undergone a myopic refractive surgery. METHODS: This prospective, interinstrument reliability analysis included 31 individuals with a previous myopic laser refractive correction. Standard keratometry and total keratometry (TK) of the flattest and steepest axis of the IOL Master 700 were compared with standard keratometry (simulated keratometry [SimK]), true net power (TNP), equivalent keratometer readings (EKR), and total corneal refractive power of the Pentacam. The Bland–Altman analysis evaluated the agreement between the measurements of both devices. A paired t-test was performed to compare the mean values of the variables obtained by the two devices. RESULTS: Mean age of the participants was 31.87 ± 13.17 years. Ten patients (32.3%) had undergone laser in situ keratomileusis surgery, and 21 (67.7%) had undergone photorefractive keratectomy surgery. The two devices generated statistically significant differences in almost all the comparisons between their corneal keratometry values, ACD, and WTW. The two devices agreed in some of the flat axis values and more specifically on SimK1 and K1, EKR K1 along 1 mm-zone and K1, as well as on the comparison between the EKR keratometry values along 1, 2, and 3 mm-zone with their corresponding TKs. CONCLUSION: IOL Master 700 and Pentacam HR do not show good concordance and cannot be used interchangeably when measuring keratometry values in postrefractive eyes, rendering the IOL power calculation in postrefractive eyes really challenging.