Refractive Index Engineering for Human Corneal Tissue by Femtosecond Laser Two‐Photon Cross‐Linking
Pengfei Qi, Ziyan Zhou, Jinshi An, Haiyi Liu, Yifan Zhang, Hai Liu, Le Chang, Yanan Wu, Yan Wang, Olga Kosareva, Andrei Savel'ev, Lie Lin, Weiwei LiuABSTRACT
Clinical refractive surgeries for myopia correction generally entail stromal tissue removal with risks of postoperative complications. NIR femtosecond laser‐induced corneal two‐photon collagen cross‐linking (two‐photon CXL) through photochemical effects can lead to localized refractive index (RI) changes in the cornea, promising for non‐ablative and non‐incisional visual correction. However, previous studies mainly focused on hydrogels and animal corneal tissues, adopting a diffraction grating method that is difficult for biological tissue. Here we systematically investigate femtosecond laser‐induced RI changes in human corneal tissue, demonstrate two‐photon excitation of riboflavin leading to cross‐linking, and employ direct interferometry to quantify RI changes. The maximum RI change is 3.80 ± 0.45 × 10 −3 in collagen hydrogel and 5.14 ± 0.75 × 10 −3 in corneal tissue. These findings illustrate that RI engineering by femtosecond laser two‐photon CXL is promising for noninvasive refractive surgery.