Effect of UVA/Riboflavin Collagen Crosslinking on Biomechanics of Artificially Swollen Corneas

PURPOSE. The purpose of this study was to characterize the relation between corneal hydration and stiffening effects of the UVA/riboflavin collagen crosslinking treatment and to investigate how artificially swelling the cornea prior to this treatment procedure affects tensile property improvement. METHODS. Porcine corneas were collagen crosslinked in vitro at different hydration levels using a number of hypoosmolar and isoosmolar riboflavin solutions. Thickness of the specimens prior to crosslinking was taken as a proxy for their hydration and was used to divide them into different thickness groups. A Dynamic Mechanical Analysis (DMA) machine was used to perform mechanical tensile tests. The hydration of specimens during the mechanical tests was kept similar to the hydration at which they were crosslinked. The recorded force was used to calculate the maximum tensile stress and tangent modulus as a function of thickness (hydration) prior to collagen crosslinking treatment. RESULTS. Collagen crosslinking with either a hypoosmolar or isoosmolar solution significantly increased corneal tensile modulus (P < 0.05). Corneas that were swollen prior to crosslinking showed significantly softer tensile properties compared with those that were crosslinked at lower hydration (P < 0.05). Although the degree of tensile property improvement was hydration dependent, the stiffness of samples crosslinked at higher hydration was not significantly different than the stiffness of those crosslinked at lower hydration when the hydration was kept similar in the mechanical experiments. CONCLUSIONS. Swelling porcine corneas to the different extents prior to collagen crosslinking treatment does not significantly change the amount of biomechanical improvement if tensile properties are measured at similar hydration.