Wavelength Optimisation in Femtosecond Laser Keratoplasty

Abstract : Purpose:Femtosecond lasers are nowadays routinely used in corneal surgery, mainly in the context of refractive surgery. Some of the clinical systems also have options for corneal grafting. However, interventions in the depth of the tissue are difficult in the case of oedematous or otherwise pathological corneas. This difficulty principally arises from the fact in those corneas, the propagation of the laser beam is perturbed by optical scattering. This phenomenon can be greatly reduced by using a better suited laser wavelength. Methods:The laser is a femtosecond Ti:sapphire laboratory laser followed by an Optical Parametric Amplifier. The wavelength can be parameters from 1200 nm to 2400 nm. Incisions are performed on human eyes obtained under permission from the French Eye Bank, Paris. These corneas are positioned on an anterior chamber which may be moved in three dimensions by a step motor system. Penetrating and lamellar incisions have been performed using different pulse energies and varying wavelengths. Results:Several experiments of incisions have been done at wavelengths around 1600 nm and have been compared to those already performed at 800 nm and 1000 nm. We have compared penetration depth and incision quality as a function of wavelength and energy. We could demonstrate a significant improvement when performing penetrating and depth lamellar keratoplasty pathological corneas using the modified wavelength. Conclusion: The use of longer infrared wavelengths for femtosecond laser keratoplasty significantly improves the quality and reproducibility of the incisions. Future systems may be further optimised by the use of deformable mirrors.