Wavelength optimization in femtosecond laser corneal surgery

To evaluate the influence of wavelength on penetration depth and quality of femtosecond laser corneal incisions in view of optimizing procedures in corneal surgery assisted by ultrashort pulse lasers. We performed penetrating and lamellar incisions on eye bank corneas using several ultrashort pulse laser sources. Several wavelengths within the near-infrared and shortwave-infrared wavelength range were used and the pulse energy was varied. The corneas were subsequently analyzed using light microscopy as well as transmission and scanning electron microscopy. We found higher penetration depths and improved incision quality when using wavelengths close to λ = 1650 nm rather than the wavelength of λ = 1030 nm typical in current clinical systems. Optical micrographs show an improvement of the penetration depth by a factor of 2 to 3 while maintaining a good incision quality when using the longer wavelength. These results were confirmed with micrographs obtained with transmission and scanning electron microscopy. A wavelength change from the standard 1030 nm to 1650 nm in corneal surgery assisted by ultrashort pulse laser considerably reduces light scattering within the tissue. This results in a better preservation of the laser beam quality in the volume of the tissue, particularly when working at depths required for deep lamellar or penetrating keratoplasty. Using this wavelength yields improved penetration depths into the tissue; it permits use of lower energies for any given depth and thus reduces unwanted side effects as thermal effects.