Repeatability and Reliability of Corneal Tomography in Keratoconus Patients with Corneal Allogenic Intrastromal Ring Segments

Abstract

Objectives: To assess the repeatability and reliability of anterior and posterior corneal measurements in keratoconus patients who underwent corneal allogenic intrastromal ring segment (CAIRS) implantation using a Scheimpflug-based tomography system. Methods: This prospective observational study included 42 eyes: 20 keratoconic eyes that had undergone CAIRS implantation and 22 healthy controls. All participants were imaged with the Pentacam HR (Oculus Optikgeräte GmbH, Germany). Each eye underwent three consecutive scans during a single session. Repeatability was evaluated using within-subject standard deviation (Sw), repeatability index (RI), and tolerance index (TI), and reliability was assessed using intraclass correlation coefficients (ICC). A TI>0.36 was considered indicative of reduced repeatability. Results: Anterior corneal curvature parameters (K1 and K2) and pachymetric indices demonstrated excellent reliability (ICC>0.90) and acceptable repeatability (TI<0.36). In contrast, CAIRS-implanted eyes exhibited greater variability in Kmax, Kmean, anterior elevation, and several posterior corneal metrics, with TI values exceeding 0.36. Despite having high ICC values, posterior elevation showed the greatest variability. Pachymetry at the corneal vertex and the thinnest corneal thickness remained highly reproducible (TI 0.08 and 0.18, respectively), suggesting strong measurement accuracy. Conclusion: The implantation of CAIRS alters the shape of the cornea and decreases the repeatability of several tomogra-phy-derived metrics, especially posterior corneal indices and Kmax. Although overall reliability remains high, clinicians should cautiously interpret small postoperative changes in monitoring these parameters. Pachymetric measurements maintain excellent precision and can be reliably used for postoperative follow-up and progression assessment after CAIRS surgery.