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

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 (K mean ), maximum keratometry (K max ), 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 K mean and K max . The CXL-plus-PTK group performed significantly better than the reference group as reflected by K max (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 K max , 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.