Comparative studies on UVA and femtosecond corneal crosslinking characterized using Brillouin microscopy

Corneal crosslinking (CXL) with UVA light is the primary treatment for keratoconus, a disease that affects cornea's stability, transparency and shape. UVA-CXL has limitations in penetration depth and unwanted irradiation on healthy tissue. As an alternative, a near-infrared femtosecond laser was used for targeted corneal crosslinking of fresh pigs' corneas. Brillouin microscopy was implemented as a non-destructive method to determine the viscoelastic properties, by measuring the Brillouin shift. We compared the Brillouin shifts measured for UVA-CXL and fs-CXL treated corneas. Measurements were also performed on UVA-CXL pure bovine collagen I in order to correlate the changes observed in CXL cornea. An increase in Brillouin shift before and after crosslinking, for both UVA and femtosecond-CXL are measurable. We demonstrate the precision and efficacy of using femtosecond CXL in spatial targeted CXL at depth in corneal tissues.