Diagnostic Value Of 3/6-Mm Corneal Curvature Ratios And Layer-Specific Indices (Asr, Spr, Apr) In Keratoconus
Published 2026 - 44th Congress of the ESCRS
Reference: PP14.018 | Type: Free paper | DOI: 10.82333/xrtq-n643
Authors: Dr Jascha Wendelstein* 1 , Dr Klemens Kaiser 2 , Giacomo Savini 3 , Dr Robert Herber 4 , Prof. Siegfried Priglinger 5 , Prof. Achim Langenbucher 6
1Ophthalmology,ludwig maximilians university ,Munich,Germany;Ophthalmology,IROC,Zürich,Switzerland, 2Ophthalmology,Frankfurt University,Frankfurt,Germany, 3Ophthalmology,Bietti Fondation,Bologna,Italy, 4Ophthalmology,Dresden,Dresden,Germany, 5Ophthalmology,Ludwig Maximilians University ,Munich,Germany, 6Experimental Ophthalmology,Saarland University,Homburg,Germany
Purpose
To determine whether the 3/6-mm corneal curvature ratios correlate with the severity of keratoconus (KCN) according to the Belin’s ABC(D) classification and to evaluate their potential as robust geometric markers for staging and disease progression.
Setting
This is a retrospective observational study included eyes of patients diagnosed with KCN who were examined at the Department of Ophthalmology, Ludwig-Maximilians-University (LMU) Munich, Germany, and the IRCCS Fondazione Bietti, Rome, Italy
Methods
This study included high-resolution anterior segment optical coherence tomography -based corneal tomography (MS-39, CSO) from 944 KCN eyes (519 patients; 67.6% male) graded using the ABC classification. For each eye, 3/6-mm ratios of epithelial, stromal, and posterior radii, as well as surface curvature ratios (anterior-stromal ratio [ASR], anterior-posterior ratio [APR], stromal-posterior ratio [SPR]), were computed. Associations with ABC stages were analyzed using linear mixed-effects models, Spearman rank correlations, and ordinal logistic regression.
Results
All analyses demonstrated that 3/6-mm curvature ratios increased systematically with keratoconus severity. Mixed-effects models identified the posterior (endothelial) 3/6-mm radius ratio as the strongest predictor across A, B, and C components (all p<0.001). Spearman correlations showed high monotonic associations, particularly for the posterior ratio (Spearman’s rho up to 0.92, p<0.001). Ordinal regression confirmed the posterior radius ratio as the most consistent predictor of higher grades A, B, and C. ASR, APR, and SPR contributed significantly to A- and C-stage prediction.
Conclusions
Central 3-mm to paracentral 6-mm corneal curvature ratios, especially the posterior 3/6-mm radius ratio and the ASR/APR/SPR metrics, provide strong, consistent indicators of keratoconus severity across all ABC stages. These ratios represent robust geometric markers with potential value for staging and progression assessment.