In the transepithelial method (Epi-On), it is not necessary to scrape the surface, i.e. remove the upper protective layer of the cornea. This method uses iontophoresis crosslinking: with the help of an iontophoresis applicator electrode, riboflavin diffuses much faster through the intact epithelium into the corneal stroma than with the usual Epi-on crosslinking procedure. This means that the process takes much less time (about 15 minutes in total). Because the epithelium remains intact, there is no corneal opacity after the procedure, no infection and no deterioration of vision. However, these drawbacks can be seen from time to time after the standard Epi-off procedure. The depth of penetration by this method is estimated at approx. 150 µm.
The surface of the eye is thus irradiated with a UV-A light source for 10 to a maximum of 30 minutes, depending on the treatment protocol chosen for the patient. During this time, the cornea is “saturated” with riboflavin, which acts as the so-called “corneal”. Photosensitizer and absorbs UV radiation. Illumination puts riboflavin in the cornea into an excited state, triggering a photochemical process that produces oxygen radicals. Oxygen radicals cause interactions with collagen in the cornea, forming bridges between collagen molecules. More than 90% of UV light is absorbed by the cornea, so there is no danger to the lens or retina of the body.