In vitro effect of corneal collagen cross-linking on corneal hydration properties and stiffness

The purpose of this study is to evaluate in-vitro the immediate effect of corneal collagen cross-linking (CXL) on corneal hydration and stiffness. Forty-two corneal buttons from freshly enucleated porcine eyes were immersed in riboflavin 0.1% in dextran 20% dilution for 3 h in order for their hydration to reach equilibrium. Corneal buttons where divided into two groups; the first group was stored in dark conditions while the other group was irradiated with UV radiation (370 nm) for 30 min to simulate CXL according to the clinically applied protocol. After irradiation, all corneas were immersed in dextran 20% solution for 3 additional hours. Subsequently, each button underwent weighing, thickness measurement, and was mounted in a special device for the measurement of force versus deformation by compression. Finally, all corneal buttons were dehydrated for 48 h in a desiccating oven set at 62 A degrees C and weighed again to obtain their dry mass. Hydration (%) of each button was calculated. Mean corneal hydration in the irradiated and the non-irradiated group of corneas was 69.8 and 72.2%, respectively (p < 0.001). Differences in thickness and compressibility were not statistically significant. Thickness and hydration were positively correlated (Pearson's r = 0.714, p < 0.001). CXL causes corneal dehydration that can be detected immediately after the procedure. This phenomenon may contribute to increased mechanical stiffness of the cornea. A change in stiffness by means of compressibility could not be detected in porcine corneas.