Systematic Differences in Corneal Curvature and Power Measurements Between the IOLMaster 700 and the Anterion and...

Background/Objectives: Corneal power has the largest impact on the variability of intraocular lens (IOL) power predictions, and corneal data from different biometers cannot be used interchangeably. We quantified the systematic differences between the Zeiss IOLMaster 700 (IOLM) and the Heidelberg Engineering Anterion and derived strategies for using both devices interchangeably in IOL power calculation. Methods: In this retrospective single-centre study, 837 eyes of 837 cataract patients were measured preoperatively with both biometers. Harmonic mean corneal front and back surface radii were derived from the flat and steep meridians, and corneal power referenced to the front apex plane was expressed as spherocylindrical power vectors (spherical equivalent, SEQ; astigmatic components C0 and C45). Three mapping strategies were compared using Bland-Altman and double-angle plots: linear regression of corneal radii without (MR) and with (MRI) intercept and multivariate linear regression of the power vector components (MMV). Results: Corneal front surface radii agreed well between devices (MR slope 1.000), whereas the IOLM reported systematically flatter posterior radii (MR slope 0.943), giving a systematically higher total corneal power (43.105 D versus 42.760 D). MRI mapping largely removed the systematic offset in the corneal radii but did not fully correct the astigmatic centroids, whereas MMV mapping aligned both the SEQ and the astigmatic centroids at the origin and yielded smaller confidence ellipses. Conclusions: Measurements from the two devices are not directly interchangeable, primarily because of systematic discrepancies in the reported posterior corneal curvature. Where identical IOL calculation concepts and formula constants are used across devices, conversion of corneal data is mandatory, and multivariate power vector mapping provides superior harmonisation compared with radius-based approaches.