UV-A/riboflavin–induced CXL has been introduced in the last decade as an in vivo cornea stiffening method. Cross-links between the collagen fibrils can be induced by photo-polymerization, leading to a stiffer fiber network.
The CXL protocol is based on three steps. First, the epithelium is removed from the central part of the cornea so that the cornea becomes permeable. Then, riboflavin solution (riboflavin 0.1% dextran T500 20%; Horus Pharma, Saint-Laurent du Var, France) is dropped on the cornea (1 drop/min for 30 minutes) in order to enable the corneal stroma to absorb the UV-light emission without damaging the deeper structures (endothelium, lens, retina). Finally, the cornea is exposed to UV-light–emitting diodes (wavelength 370 nm, intensity 3 mW/cm2; IROC Medical, Zurich, Switzerland) for 30 minutes while riboflavin drop is continued (1 drop every 5 minutes). In our experiments, the diameter of the irradiated area was set to 8 mm.