Two‐photon collagen crosslinking in ex vivo human corneal lenticules induced by near‐infrared femtosecond laser

Abstract

Myopia and keratoconus have become common corneal diseases that threaten the quality of human vision, and keratoconus is one of the most common indications for corneal transplantation worldwide. Collagen crosslinking (CXL) using riboflavin and ultraviolet A (UVA) light is an effective approach for treating ophthalmic disorders and has been shown clinically not only to arrest further progression of keratoconus but also to improve refractive power for cornea. However, CXL surgery irradiated by UVA has various potential risks such as surface damage and endothelial cell damage. Here, near‐infrared femtosecond laser‐based two‐photon CXL was first applied to ex vivo human corneal stroma, operating at low photon energy with high precision and stability. After two‐photon CXL, the corneal stiffness can be enhanced by 300% without significantly reducing corneal transparency. These findings illustrate the optimized direction that depositing high pulses energy in corneal focal volume (not exceeding damage threshold), and pave the way to 3D CXL of in vivo human cornea with higher safety, precision, and efficacy.

Ultrabroadband two-beam CARS as a tool in diagnostics and therapy

“…Due to their high peak intensities at low pulse energies, fs-laser pulses allow for gentle tissue treatment with minimum side effects. The collagen fibers in the cornea, for example, may be cross-linked by two-photon fs-excitation [1], or cancer cells may be removed by fs-laser ablation [2]. In a compact treatment scenario, simultaneous in-situ diagnostics of molecular species and their environments is therefore desirable.…”

Two-Photon Imaging for Non-Invasive Corneal Examination

“…• Two-photon photoactivation of riboflavin can efficiently increase corneal stiffness. [190][191][192][193][194] TPEF-two-photon excited fluorescence; SHG-second-harmonic generation; FLIM-fluorescence lifetime imaging microscopy; ST-structure tensor; FT-Fourier Transform.…”

“…However, this was reliant on reduction in treatment specificity and an increase in the mean laser power, well above hazardous values. Recently, the two-photon excited CXL in human tissue was also demonstrated [193,194].…”