Biomechanical stiffening effect in ultra-high-fluence extracorporeal cross-linked corneal allogenic intrastromal ring segments

Abstract

Purpose: To compare the biomechanical stiffening effects of a novel ultra-high fluence corneal cross-linking (CXL) protocol with conventional high-fluence CXL for extracorporeal corneal allogenic intrastromal ring segment optimization (ECO-CAIRS).

Setting ELZA Institute, Zurich, Switzerland.

Design: Experimental, randomized, controlled ex vivo laboratory study using porcine corneas. No mask-ing was applied.

Methods: Eighty-four porcine corneas were divided into four groups: Group A (control), Group B (10 J/cm2), Group C (30 J/cm2), and Group D (60 J/cm2). Following epithelial debridement, Groups B, C, and D were treated with 0.1% hypo-osmolar riboflavin. UV-A irradiation was delivered at fluences of 10 J/cm2 (18 mW/cm2, 9:15 min) for Group B, 30 J/cm2 (30 mW/cm2, 16:40 min) for Group C, and 60 J/cm2 (30 mW/cm2, 33:18 min) for Group D. Corneal biomechanical properties were assessed via stress-strain extensiometry.

Results: Mean elastic modulus (5% strain) values were: Group A (1.39 ± 0.49 N/mm), Group B (1.83 ± 0.48 N/mm), Group C (2.25 ± 0.83 N/mm), and Group D (2.31 ± 0.88 N/mm). Ultra-high fluence groups (C and D) showed significantly greater stiffening than Group B (P = 0.041 and P = 0.015), with no significant difference between Groups C and D (P = 1.00). Group B exhibited significantly greater stiffening than Group A (P = 0.023).

Conclusions: Ultra-high fluence CXL enhances biomechanical stiffening compared to conventional high-fluence CXL, supporting its use in ECO-CAIRS. In this extracorporeal context, endothelial safety and haze are irrelevant, while increased stiffness facilitates intrastromal ring insertion and re-duces corneal swelling.