Corneal curvature gradient determines corneal healing process and epithelial behavior.

We read with great interest the article by Kanellopoulos and Asimellis1 and the subsequent correspondence with Reinstein et al.2 with the debate regarding the law that drives epithelial remodeling and the healing process. Kanellopoulos and Asimellis explained their findings of epithelial thickening after myopic LASIK with their hypothesis that epithelial behavior is related to the biomechanics of the cornea and that a thinned cornea (in cases of large myopic ablation) might be more susceptible to epithelial hyperactivity and regrowth. Conversely, Reinstein et al. suggested that all epithelial thickness changes can be explained by a compensatory mechanism that is driven by the rate of change of curvature of the stromal surface. This last finding was presented in an article by our group that defined the rate of change of curvature as the corneal curvature gradient.3 In particular, the curvature gradient is a topography map aimed to evaluate the rate of change in curvature over the corneal surface. In that article, we demonstrated that the initial curvature gradient after excimer ablation predicts the change in tangential curvature over the subsequent 12 months in areas where the initial tangential curvature is the greatest. When the curvature gradient is high, the surface curvature modification remains in progress even months after the ablation. We believe the hypothesis by Kanellopoulos and Asimellis (that biomechanics could play a role in corneal healing) is interesting and we cannot exclude it, but it currently lacks validation with preclinical and clinical studies that separate the possible biomechanical effect from the curvature gradient change. With the current evidence we believe that all epithelial thickness changes, even those described by Kanellopoulos and Asimellis, could be explained by a change in the curvature gradient. We would like to divide the categorical evidence into Clinical, Cell Morphology, Modelling, and Real Life.