Total Corneal Aberration Measurements by Anterior Segment Optical Coherence Tomography and Scheimpflug-Based Imaging: A Narrative Review of Optical Principles and Sources of Inter-Device Discordance

This is the authors' abstract. We don't add key points for this paper.

Total corneal aberration analysis is increasingly used as part of intraocular lens selection, ectasia screening, and refractive surgery planning. Scheimpflug-based tomography and anterior segment optical coherence tomography (AS-OCT) are commonly used imaging techniques to identify the anterior and posterior corneal surfaces; however, many devices combine these methods with Placido-disc topography or reconstruction algorithms. Although these devices provide anterior, posterior, and total corneal wavefront aberrations, multiple studies have shown that Zernike coefficients obtained with different systems are not consistently interchangeable, particularly for posterior-surface-derived and higher-order terms such as trefoil and total higher-order aberration root-mean-square values. This narrative review summarizes the optical principles of Scheimpflug imaging and AS-OCT, synthesizes the available comparative literature, and analyzes the mechanisms that may contribute to inter-device discordance, including differences in light sources and light-tissue interactions, posterior-surface reconstruction and refractive-index assumptions, edge-detection and Zernike-fitting algorithms, sampling geometry and acquisition time, and reference-axis selection. We discuss the clinical implications of these discrepancies and propose a research agenda, including model-eye validation and ray-tracing simulation studies, to help distinguish the effects of hardware optics from those of proprietary reconstruction algorithms.