ESCRS - FP06.04 - Applicability Of The Step Grading System To Ms-39 Oct Measurements And Evaluation Of Epithelial And Stromal Parameters For Early Keratoconus Diagnosis

Applicability Of The Step Grading System To Ms-39 Oct Measurements And Evaluation Of Epithelial And Stromal Parameters For Early Keratoconus Diagnosis

Published 2026 - 44th Congress of the ESCRS

Reference: FP06.04 | Type: Free paper | DOI: 10.82333/z0qc-pv08

Authors: Dr Chiara Muzio* 1 , Dr Francesco Pozzo Giuffrida 2 , Cecilia Acuti Martellucci 3 , Mirko Verderio 4 , Dr Andrea Sperti 5 , Dr Marco Nassisi 6 , A/Prof. Francesco Viola 6 , Dr Saverio Vincenzo Luccarelli 6

1Department of Clinical Sciences and Community Health,University of Milan,Milan,Italy;Ophthalmology Unit,ASST Fatebenefratelli Sacco – Ospedale Fatebenefratelli e Oftalmico,Milan,Italy, 2Ophthalmology Division,Foundation IRCCS Ca' Granda Ospedale Maggiore Policlinico,Milan,Italy;Department of Ophthalmology,Bascom Palmer Eye Institute,Miami,United States, 3Department of Medical and Surgical Sciences,University of Bologna,Bologna,Italy, 4Ophthalmology Division,Foundation IRCCS Ca' Granda Ospedale Maggiore Policlinico,Milan,Italy, 5Ophthalmology Unit,IRCCS Policlinico San Donato,San Donato Milanese,Italy, 6Department of Clinical Sciences and Community Health,University of Milan,Milan,Italy;Ophthalmology Division,Foundation IRCCS Ca' Granda Ospedale Maggiore Policlinico,Milan,Italy

Purpose

To evaluate whether the STEP grading system can also be applied to epithelial and stromal thickness parameters derived from the MS-39 OCT, and to determine the diagnostic performance of MS-39–derived epithelial, stromal, and epithelial-to-stromal ratio parameters for early keratoconus detection.

Setting

Department of Clinical Sciences and Community Health, University of Milan; Ophthalmology Division, Foundation IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy.

Design: Retrospective observational study.

Methods

A total of 313 eyes (103 normal, 210 keratoconus) were analyzed. MS-39 epithelial and stromal thickness parameters were extracted from the same map locations used in the original STEP study. Intersectoral differences, minimum and maximum thickness values, and epithelial-to-stromal ratios were calculated. The diagnostic performance of each parameter was assessed using ROC analysis, with area under the curve (AUC), sensitivity, and specificity calculated.

Results

The MS39-derived stromal parameters demonstrated reduced diagnostic performance compared with values reported in the original STEP publication. In our population, the greatest discriminatory ability between keratoconus and normal corneas was observed for parameters derived from intersectoral epithelial and stromal differences, as well as for the epithelial-to-stromal ratio. The epithelial thickness difference between superonasal and inferotemporal sectors (2–4 mm) showed the highest AUC (0.798; 95% CI, 0.749–0.847). The epithelial-to-stromal ratio in the superonasal sector (2–4 mm) had an AUC of 0.788 (95% CI, 0.735–0.841).

Conclusions

The STEP grading system may not be directly applicable to MS-39 measurements, as inter-device variability in stromal thickness limits straightforward translation of thresholds established on RTVue-XR SD-OCT. Epithelial-derived metrics, particularly intersectoral differences and the epithelial-to-stromal ratio, demonstrated the strongest diagnostic performance and may serve as more stable markers across devices. These findings support the need for device-specific threshold calibration when applying the STEP system to different platforms.