Independent-Effect Comparison of Five Crosslinking Procedures for Progressive Keratoconus Based On Keratometry and ABCD Grading System Using Generalized Estimating Equations (GEE)

Abstract

Purpose: Corneal collagen crosslinking (CXL) is a newly treatment for progressive keratoconus. Several CXL modalities were developed clinically. However, few comparative researches about the effectiveness of multiple CXL modalities exist. This study is to compare the 1-year outcomes of five CXL procedures for progressive keratoconus using generalized estimating equations (GEE) to remove the effect of age, baseline data and bilateral surgery in a Chinese population. Methods: This retrospective study included 213 eyes of 154 patients with keratoconus who underwent CXL and were observed for 1 year. Five CXL procedures were assessed, including accelerated transepithelial corneal-crosslinking (ATE CXL), iontophoresis corneal-crosslinking (I-CXL) for 10 min, CXL plus phototherapeutic keratectomy (PTK), high-fluence accelerated corneal crosslinking (High-Fluence A-CXL), and accelerated corneal cross-linking (A-CXL). Patients treated with A-CXL represented the reference group. Primary outcomes were the changes of visual acuity, spherical equivalence, endothelial cell density (ECD)，mean keratometry (Kmean), maximum keratometry (Kmax), minimum corneal thickness (MCT), A (staging index for ARC; ARC = anterior radius of curvature), B (staging index for PRC, PRC = posterior radius of curvature), and C (staging index for MCT) value 1-year postoperatively compared with baseline. Secondary outcomes were comparisons of corrected GEE from each procedure versus the A-CXL group.Results: The A-TE CXL group performed worse than A-CXL group with Kmean and Kmax. The CXL-plus-PTK group performed significantly better than the reference group as reflected by Kmax (β = -0.907, P = 0.049). However, the CXL-plus-PTK group performed worse on B and C, which the I-CXL for 10 min group performed better. The corneal capacity of five eyes from three pediatric patients who underwent High-Fluence A-CXL procedure was measured.Conclusions: The CXL-plus-PTK procedure appeared to have better efficacy than the A-CXL procedure based on Kmax, and the I-CXL for 10 min procedure performed better based on the ABCD Grading System. Stronger protection of the cornea should be taken for pediatric patients who undergo the High-Fluence A-CXL procedure.