Model for Optimization of the UV-A/Riboflavin Strengthening (cross-linking) of the Cornea: Percolation Threshold.

To achieve the maximum level of collagen strengthening within the shortest treatment time possible, we have developed a mathematical model which is used to optimize the process of corneal cross-linking. This model is able to predict the temporal and spatial distribution of generated cross-links within the corneal stroma and hence the increase in the elasticity modulus. Theory predicts corneal strengthening at low radiation intensities and the absence of the strengthening effect at radiation intensities above the threshold level, which agrees with the experimental results. The model takes account of the initial riboflavin concentration and bleaching, light intensity and time of illumination.