Repeatability Analysis Of Ms-39 Indices Pre And Post Cross-Linking For The Evaluation Of Progressive Keratoconus

This study aims to assess the repeatability of indices utilized in keratoconus screening and progression and to develop a methodology for assessing the statistical significance of corneal changes over time by juxtaposing them with the inherent repeatability of the measuring device

Humanitas Clinical and Research Center, Milan, Italy; Department of Ophthalmology, Univ. Hospital Carl Gustav Carus, TU Dresden, Germany; Muscat Eye Laser Center - Oman. Cornea, Cataract & Refractive Surgery Unit, Vissum (Miranza Group), Alicante, Spain.

A retrospective analysis was conducted on a cohort of patients with varying degrees of keratoconus from four distinct eye clinics, who underwent OCT-based corneal topographic examinations using the MS-39 (Costruzione Strumenti Oftalmici - Florence, Italy). The evaluated diagnostic indices include endpoints from corneal thickness and anterior and posterior corneal surface in term of symmetry expressing the likelihood of keratoconus. Analysis involved characterizing standard deviation (SD), Coefficient of Variation (CV%) and confidence interval (CI) as functions of index severity. Correlations between pre/post-CXL status and scanning modality were also conducted to assess repeatability dependency on the subclass.

The dataset analyzed comprised 271 eyes of 198 patients (three scans per eye), both pre and post-CXL procedure, acquired using either the "Anterior segment" or "Cornea" modality. The data showed good repeatability for all indices, with CV% values (average over the entire interval) ranging from 0.23% to 6.08% (KFAVG = 0.23%, KFMAX = 0.51%, SIF = 2.95%, CSIF = 4.16%, EIF = 2.73%, RMSF = 3.21%, KBAVG = 0.69%, KBMAX = 0.97%, SIB = 3.62%, CSIB = 6.08%, EIB= 3.21%, RMSB = 2.92%, CCT = 0.43%, ThkMin = 0.48%, ThkSI = 4.21%, PTI = 4.98%). Not clinically significant difference between pre- and post-CXL were found, indicating that the repeatability of the device is not affected by the procedure, nor between scan modalities.

This study presents a comprehensive evaluation of the repeatability of diagnostic indices employed in keratoconus screening, providing essential insights into disease progression assessment and the reliability of these indices in early and post-CXL conditions.