Inter-device Agreement and Normative Corneal Parameters in Adolescents and Young Adults: A Structured Narrative Review

Accurate characterization of the corneal surface is essential for clinical decision-making in optometry and ophthalmology, particularly in the context of myopia management and early detection of ectatic disorders. Optical imaging technologies, including Placido-based topography, Scheimpflug tomography, and optical coherence tomography (OCT), are widely used to assess corneal geometry, yet their measurements are not fully interchangeable. This study was conducted as a structured narrative review that summarizes recent evidence (2020-2025) on inter-device agreement and synthesizes normative corneal geometric parameters in secondary school and university-aged populations. A structured literature search identified studies evaluating agreement between two or more corneal imaging technologies, as well as studies reporting normative corneal parameters in individuals aged 12 to 25 years. Findings were synthesized narratively due to heterogeneity in study designs and reported outcomes. Thirty-five studies compared measurements across devices, and forty-five studies provided normative data. Most devices showed high correlation for central anterior keratometry (simulated keratometry (Sim-K); typically r>0.95), with consistent mean Sim-K differences of 0.10-0.25 D between Placido and Scheimpflug systems. Scheimpflug tomography generally reported steeper posterior curvature and greater posterior elevation than OCT, while OCT yielded corneal pachymetry values approximately 10-20 μm thicker than Scheimpflug tomography. These systematic differences reflect the distinct measurement principles of each technology and underscore their non-interchangeability. Normative data from school-aged populations revealed meaningful variability in corneal curvature, asphericity, and thickness across ethnic and refractive groups, with East Asian cohorts typically exhibiting flatter corneas and less prolate asphericity. Overall, Scheimpflug and OCT technologies provide more comprehensive corneal assessment than Placido-based topography, particularly for posterior corneal geometry and pachymetry. Population-specific normative values and awareness of device-specific measurement differences are essential for accurate diagnosis, myopia management, and refractive surgery screening in adolescents and young adults.