# Stromal Curvature, Power and Corneal‐Stromal Curvature Ratios From a Hybrid AS‐OCT in Eyes With Keratoconus

## TL;DR

This study uses OCT to analyze stromal curvature and corneal power in keratoconus, showing that three-surface models better capture changes in advanced cases.

## Contribution

The study introduces stromal curvature ratios as novel structural metrics for staging keratoconus severity.

## Key findings

- Peripheral zones show less curvature variability compared to central zones in keratoconic eyes.
- Three-surface models yield different corneal power estimates than simplified models in advanced keratoconus.
- Curvature ratios increase with keratoconus severity, reflecting posterior steepening and anterior-posterior decoupling.

## Abstract

To characterise stromal curvature and curvature ratios in keratoconus (KCN) using anterior segment OCT, and to evaluate the implications of using single‐, two‐, and three‐surface refractive models for corneal power estimation in ectatic eyes.

Retrospective observational study. Anterior segment OCT measurements (MS‐39, CSO) were analysed. Anterior, stromal, and posterior curvature radii were computed across five concentric zones (2.0–6.0 mm) using a floating best‐fit sphere, and curvature ratios were subsequently derived: anterior‐to‐stromal (ASR), stromal‐to‐posterior (SPR), and anterior‐to‐posterior (APR). Corneal power was calculated using one‐, two‐, and three‐surface models. KCN severity was classified according to the Belin ABC grading stage and ASR, SPR, and APR were stratified accordingly.

Data from 944 keratoconic eyes were analysed. Peripheral zones (6.0 mm) exhibited reduced variability in curvature measurement compared to central zones (3.0 mm). Differences between simplified (one‐ and two‐surface) and three‐surface power models correlated moderately with increased APR and SPR values. ASR, SPR, and APR all increased progressively with advancing ABC grade.

In advanced keratoconus, three‐surface modelling yields different corneal power estimates versus simplified models in KC; prospective outcome studies are needed to assess clinical impact. Stromal curvature and its derived ratios provide novel structural metrics that change with KCN severity. Curvature ratio increase —especially APR and SPR— reflects posterior steepening and anterior–posterior decoupling, with possible implications for staging and surgical planning.