Importance of wavelength for ultrashort laser pulses in healthy and pathological corneas

A study on the role of laser wavelength in keratoplasty assisted by ultrashort pulse lasers is presented. This article gives a summary of the principal physical mechanisms contributing to the transparency of healthy corneas and presents transparency measurements as well as laboratory experiments on tissue with lasers at different wavelengths. The transparency of a healthy cornea is strongly related to its regular structure at micrometer and nanometer length scales. Many indications for keratoplasty are associated with a perturbation of this structure and therefore with a sometimes strongly reduced tissue transparency. This explains the often unsatisfactory results obtained when using ultrashort pulse lasers for the procedure. Theoretical considerations and laboratory experiments show that the light scattering processes responsible for the loss in laser beam quality depend strongly on wavelength and the use of wavelengths longer than those presently used allows these processes to be almost completely eliminated. The use of a spectral transparency window close to 1.65 A mu m is suggested. The use of laser wavelengths close to 1.65 A mu m represents an interesting alternative for the improvement of keratoplasty assisted by ultrashort pulse lasers.