LAUSR

PURPOSE To assess whether full biomechanical stiffening can be achieved with corneal crosslinking (CXL) when applying a reduced ultraviolet (UV) fluence during the standard irradiation time. SETTING Laboratory of Ocular Cell Biology, Center for Applied Biotechnology and Molecular Medicine, University of Zurich, Zurich, Switzerland. DESIGN Experimental study. METHODS Thirty-four freshly enucleated porcine corneas were deepithelialized and soaked with hypoosmolar riboflavin 0.1% solution for 30 minutes. Slow low-irradiance CXL (30 minutes at 1.5 mW/cm2, fluence 2.7 J/cm2) was compared with standard CXL (30 minutes at 3 mW/cm2, fluence 5.4 J/cm2). The controls were soaked with riboflavin but not exposed to UV light. Elastic (stress-strain) and viscoelastic (stress-relaxation) 2-dimensional testing was performed with a commercial stress-strain extensometer to quantify the biomechanical stiffening. RESULTS Corneas crosslinked with low and standard UV irradiances had a significantly higher mean elastic modulus (65.9 MPa ± 15.7 [SD] and 67.1 ± 15.6 MPa, respectively) than controls (52.4 ± 12.3 MPa) (P < .001). Also, the remaining stress after 120 seconds of stress-relaxation was significantly higher after CXL with low and standard UV irradiances (159 ± 21 kPa and 158 ± 25 kPa, respectively) compared with controls (135 ± 20 kPa) (P ≤ .013). No difference was observed in low and standard irradiances between CXL conditions (P = .64). CONCLUSIONS The UV fluence for CXL might be reduced while maintaining the biomechanical efficacy by using a lower UV irradiance and the same irradiation duration. This might open avenues in the treatment of extremely thin corneas.