Epithelium-off CXL involves gently removing the layer of skin, called the epithelium that covers the cornea. Then the riboflavin eye drops are placed on the cornea and the cornea is exposed to UV light. We have longer clinical experience with Epi-off CXL, and most studies evaluating the effect of CXL has been with the epi-off technique.
Epithelium-on CXL does not remove the epithelium of the cornea.