A normal cornea has crosslinks between its collagen fibers that keep it strong and able to maintain its natural shape. The cornea naturally creates new collagen crosslinks in response to damage from smoking, diabetes mellitus, and aging.
Corneal collagen cross-linking involves saturating the cornea with a photosensitizer – ophthalmic riboflavin (vitamin B2) solution – followed by UVA irradiation. Photo-oxidative damage induces new collagen crosslinks to stiffen and stabilize the cornea. If corneal thickness is less than 400 microns, cross-linking should be avoided.
In CXL procedure (standard protocol), topical anesthesia is administered to numb the cornea. The front surface of the cornea — the epithelium — is mechanically removed/destroyed to expose the corneal stromal tissue. Riboflavin solution is then administered topically. Next, the cornea is irradiated with a UVA light source for a pre-determined period of time. Postoperatively, antibiotics and corticosteriod drops are administered and a bandaid contact lens is applied. The bandaid contact lens remains in place for a few days while the epithelium heals.
Some surgeons prefer to leave the epithelium intact during the cross-linking procedure. The epithelium-on technique is associated with less pain and faster postoperative recovery, but is reported by proponents of the standard protocol to be less effective. There is ongoing debate among eye surgeons as to which technique is superior.