Corneal collagen cross-linking (CXL) in thin corneas

Corneal collagen cross-linking (CXL) is a therapeutic procedure aiming at increasing the corneal stiffness in the keratoconus eyes by induction of cross-links within the extracellular matrix. It is achieved by ultraviolet-A (370 nm) irradiation of the cornea after saturation with the photosensitizer riboflavin. In the conventional CXL protocol, a minimum de-epithelialized corneal thickness of 400 μm is recommended to avoid potential irradiation damage to the corneal endothelium. In advanced keratoconus, however, stromal thickness is often lower than 400 μm, which limits the application of CXL in that category. Efforts have been undertaken to modify the conventional CXL procedure to be applicable in thin corneas. The current review discusses different techniques employed to achieve this end and their results. The overall safety and efficacy of the modified CXL protocols are good, as most of them managed to halt the progression of keratectasia without postoperative complications. However, the evidence of safety and efficacy in the use of modified CXL protocols is still limited to few studies with few patients involved. Controlled studies with long-term follow-up are required to confirm the safety and efficacy of the modified protocols.