Biological and biomechanical responses to traditional epithelium-off and transepithelial ribofl avin-UVA CXL techniques in rabbits

PURPOSE: To compare the biological effects of ribofl avinultraviolet A (UVA) corneal cross-linking (CXL) performed with a traditional epithelium-off method to several transepithelial methods in a rabbit model. Preliminary experiments on biomechanical rigidity were also performed. METHODS: Four treatment groups were included: (1) standard epithelium-off, (2) tetracaine transepithelial, (3) benzalkonium chloride-ethylenediaminetetraacetic acid (BKC-EDTA) transepithelial, and (4) femtosecond laser-assisted transepithelial ribofl avin-UVA CXL. Six eyes from each treatment group and the untreated control group were analyzed at 24 hours and 2 months after treatment in wound healing studies. The TUNEL assay was performed to detect the extent of stromal cell death. Optical density was measured with a Scheimpfl ug analyzer. The corneal stiffening effect was quantitated in three eyes from each group using optical coherence elastography performed 2 months after treatments. RESULTS: Twenty-four hours after CXL, stromal cell death extended full corneal thickness with both standard epitheliumoff CXL and femtosecond laser-assisted CXL, but only approximately one-third stromal depth after BKC-EDTA transepithelial CXL. Negligible stromal cell death was detected with tetracaine transepithelial CXL. Cell death results were statistically different between the BKC-EDTA transepithelial CXL and standard epithelium- off CXL groups (P < .0001). Signifi cant corneal opacity differences were noted. Standard epithelium-off CXL had the greatest density and tetracaine transepithelial CXL had the least density compared to the control group after treatment. As measured with optical coherence elastography, a trend toward greater mean stiffening was observed with BKC-EDTA transepithelial CXL than with epithelium-off CXL, femtosecond laserassisted CXL, or tetracaine transepithelial CXL, but the result did not reach statistical signifi cance. All of the CXL treatment groups exhibited signifi cantly smaller variance of stiffness compared to the control group. CONCLUSION: In the rabbit model, BKC-EDTA transepithelial CXL produced less stromal cell death and less risk of endothelial cell damage than standard epithelium-off CXL or femtosecond laser-assisted CXL. Additional study is needed to determine whether biomechanical stiffness is signifi cantly different between the epithelium-off CXL and transepithelial CXL groups.