Biomechanical and histological changes after corneal crosslinking with and without epithelial debridement

TLDR

The study aimed to evaluate the biomechanical effectiveness of corneal crosslinking with riboflavin without epithelial removal (C3‑R) compared to standard crosslinking. Rabbits underwent three crosslinking protocols—standard with epithelial removal, and two non‑epithelial‑removal protocols using benzalkonium chloride or preservative‑free oxybuprocaine—each receiving riboflavin and 30‑minute UVA irradiation (3 mW/cm²), followed by euthanasia 24 h later. C3‑R produced a 21% increase in Young’s modulus and limited keratocyte loss to the superficial 200 µm, whereas standard crosslinking yielded a 102% modulus rise and complete stromal cell loss; the reduced biomechanical effect and shallower cytotoxicity make C3‑R unsuitable for routine keratoconus treatment but potentially useful for corneas thinner than 400 µm.

Abstract

To test the biomechanical efficiency of corneal crosslinking with riboflavin without epithelial debridement (C3-R).Moscow Helmholtz Research Institute of Eye Diseases, Moscow, Russia.The left eyes of rabbits were crosslinked using standard crosslinking including epithelial removal (Group 1), using benzalkonium chloride-containing proxymetacaine eyedrops without epithelial removal (Group 2), or using preservative-free oxybuprocaine eyedrops without epithelial removal (Group 3). All left eyes received riboflavin solution and were irradiated with an ultraviolet-A double diode for 30 minutes (irradiance 3 mW/cm(2)). The animals were killed 1 day after crosslinking. Biomechanical and histological analyses were performed.Fourteen eyes were evaluated. There was a statistically significant increase in Young's modulus in Group 1 (102.45%) and in Group 2 (21.30%). In Group 3, no biomechanical changes were measured. Histology showed complete cell loss of keratocytes and endothelium in Group 1 and inhomogeneous keratocyte loss down to 200.0 microm in Group 2. No changes were observed in Group 3.Corneal crosslinking without epithelial debridement reduced the biomechanical effect by approximately one fifth compared with standard crosslinking, probably because of restricted and inhomogeneous stromal distribution of riboflavin. The cytotoxic damage was restricted to 200.0 microm stromal depth, which is an advantage over the standard method. Therefore, C3-R is not recommended for the routine treatment of keratoconus but primarily for cases with a corneal thickness less than 400.0 microm in which standard crosslinking cannot be used without serious risk to the endothelium.