New compact femtosecond laser source for penetrating keratoplasty at 1.65 μm

Femtosecond laser surgery in the volume of corneal tissue is typically performed wavelengths of about 1 μm, which gives excellent results on transparent corneas. However, the outcome is much worse in the case of oedematous or pathological corneas as the laser beam propagation is disturbed by optical scattering. Our studies suggest that this phenomenon can be greatly reduced by using a better suited laser wavelength. Best results are obtained at 1.65 μm. Currently, no compact femtosecond laser at this wavelength is commercially available. We have developed a new simple, compact and stable laser source consisting of a non linear crystal pumped by a compact commercial solid-state laser emitting at 1.03 μm in a configuration of an Optical Parametric Generation (OPG). The output wavelength of this system can be tuned in the spectral range of 1.45 - 1.8 μm. A series of ex vivo penetrating incisions using energies of the order of a few microjoules on corneal tissues have been performed while varying the wavelengths from 1.45 μm to 1.7 μm. The results have been compared to experiments performed at 0.8 μm and 1 μm. The use of longer infrared wavelengths around 1.65 μm for femtosecond laser keratoplasty significantly improves the quality and the penetration depth of incision in case of pathological tissues, without inducing any additional side effects.