Precision In Corneal Epithelium Mapping: Assessing Progression Thresholds In Diverse Keratoconus Stages

This study aims to evaluate the repeatability and reproducibility of corneal epithelium thickness (ET) measurements using a spectral-domain optical coherence tomographer (SD-OCT)/Placido topographer (MS-39, CSO, Florence, Italy) in a keratoconus (KC) population across various stages and to establish progression thresholds for assessing KC advancement.

A prospective hospital setting.

In this study, 149 eyes were categorized into four groups: forme fruste keratoconus (FFKC) (29 eyes), mild KC (34 eyes), moderate KC (40 eyes), and severe KC (46 eyes). We utilized the within-subject standard deviation (Sw), test-retest variability (TRT), coefficient of variation (CoV), and intraclass correlation coefficient (ICC) to assess intraoperator repeatability and interoperator reproducibility.

The MS-39 demonstrated acceptable repeatability and reproducibility in KC patients, with ICC values ranging from 0.732 to 0.954. However, patients with more advanced KC stages and progressive peripheralization of measurement points exhibited higher TRTs alongside a thinning trend. This study proposes cut-off values for mild, moderate, and severe KC at 4.9 µm, 5.2 µm, and 7.4 µm, respectively, for thinnest epithelium thickness (TET). For central epithelium thickness (CET), the recommended cut-off values for mild, moderate, and severe KC are 2.8 µm, 4.4 µm, and 5.3 µm, respectively, potentially aiding in keratoconus diagnosis and monitoring.

This study revealed a decrease in the precision of the MS-39 when measuring patients with more severe KC and at more peripheral corneal points. Given the significant variance in ET measurements by MS-39 across different KC stages, accurate grading of KC patients is essential to minimize errors in clinical decision-making.