Establishing Corneal Cross-Linking With Riboflavin and UV-A in the Mouse Cornea In Vivo: Biomechanical Analysis

PURPOSE. To establish corneal cross-linking (CXL) with riboflavin and UV-A in in the mouse cornea in vivo and to develop tools to measure the biomechanical changes observed. METHODS. A total of 55 male C57BL/6 wild-type mice (aged 5 weeks) were divided into 14 groups. Standard CXL parameters were adapted to the anatomy of the mouse cornea, and riboflavin concentration (0.1%-0.5%) and fluence series (0.09-5.4 J/cm(2)) were performed on the assumption of the endothelial damage thresholds. Untreated and riboflavin only corneas were used as controls. Animals were killed at 30 minutes and at 1 month after CXL. Corneas were harvested. Two-dimensional (2D) biomechanical testing was performed using a customized corneal holder in a commercially available stress-strain extensometer/indenter. Both elastic and viscoelastic analyses were performed. Statistical inference was performed using t-tests and specific mathematical models fitted to the experimental stress-strain and stress-relaxation data. Adjusted P values by the method of Benjamini and Hochberg are reported. RESULTS. For all CXL treatment groups, stress-relaxation showed significant differences (P < 0.0001) after 120 seconds of constant strain application, with cross-linked corneas maintaining a higher stress (441 +/- 40 kPa) when compared with controls (337 +/- 39 kPa). Stress-strain analysis confirmed these findings but was less sensitive to CXL-induced changes: at 0.5% of strain, cross-linked corneas remained at higher stress (778 +/- 111 kPa) when compared with controls (659 +/- 121 kPa). CONCLUSIONS. Cross-linking was induced in the mouse cornea in vivo, and its biomechanical effect successfully measured. This could create opportunities to study molecular pathways of CXL in transgenic mice.