With the advent of CXL collagen crosslinking for the treatment of keratoconus various application techniques have been developed. Initially crosslinking was done with the outer skin epithelial layer intact or "epithelium ON" techniques. This is how the first crosslinking procedures were performed. Some Doctors question the effectiveness of the Epithelium on technique. Some surgeons thinks the epithelium on technique has less penetration of the riboflavin eye drops that is absorbed into the lower stroma layer below the epithelial skin layer making crosslinking less effective. The doctors base this upon a higher retreatment rate with epithelium on crosslinking. With some surgeons the the standard of care is the "epithelium OFF" technique where the epithelial skin layer is removed and the underlying stroma is exposed for the application of the riboflavin eye drops. With the Riboflavin being directly applied to the stroma unlike epithelium on crosslinking, there is a better absorption on the riboflavin eye drops in the corneal stroma. Surgeon in Europe find this to be possibly more effective than epithelium techniques and epithelium off crosslinking seems to be their standard of care for the treatment of keratoconus