Author(s): Schumacher S, Mrochen M, Wernli J, Bueeler M, Seiler T, Schumacher S, Mrochen M, Wernli J, Bueeler M, Seiler T, Schumacher S, Mrochen M, Wernli J, Bueeler M, Seiler T, Schumacher S, Mrochen M, Wernli J, Bueeler M, Seiler T
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Abstract PURPOSE: To develop a theoretical model for riboflavin ultraviolet-A cross-linking treatment that can predict the increase in stiffness of the corneal tissue as a function of the ultraviolet intensity and riboflavin concentration distribution, as well as the treatment time. METHODS: A theoretical model for calculating the increase in corneal cross-linking (polymerization rate) was derived using Fick's second law of diffusion, Lambert-Beer's law of light absorption, and a photopolymerization rate equation. Stress-strain experiments to determine Young's modulus at 5\% strain were performed on 43 sets of paired porcine corneal strips at different intensities (3-7 mW/cm²) and different riboflavin concentrations (0.0\%-0.5\%). The experimental results for Young's modulus increase were correlated with the simulated polymerization increase to determine a relationship between the model and the experimental data. RESULTS: This model allows the calculation of the one-dimensional spatial and temporal intensity and concentration distribution. The total absorbed radiant exposure, defined by intensity, concentration distribution, and treatment time, shows a linear correlation with the measured stiffness increase from which a threshold value of 1.7 J/cm² can be determined. The relative stiffness increase shows a linear correlation with the theoretical polymer increase per depth of tissue, as calculated by the model. CONCLUSIONS: This theoretical model predicts the spatial distribution of increased stiffness by corneal cross-linking and, as such, can be used to customize treatment, according to the patient's corneal thickness and medical indication.
This article was published in Invest Ophthalmol Vis Sci
and referenced in Journal of Biomedical Engineering and Medical Devices