Laser thermal keratoplasty using a continuous wave diode laser

BACKGROUND: Laser thermal keratoplasty is currently performed with a pulsed Ho:YAG laser at 2.07 mu m wavelength. Long-term stability depends critical ly on the coagulation depth of each cone and thus on emission wavelength (a bsorption in corneal tissue) and focusing, all contributing to controlled s table collagen shrinkage. To achieve this, a temperature range of 65 degree s to 90 degrees C is needed. A continuous wave laser source meets the coagu lation requirements more effectively by avoiding tissue cooling by thermal diffusion as well as the peak temperatures of pulsed lasers, which countera cts the intended central corneal steepening. METHODS: A continuous wave diode laser was developed, emitting at 1.885 mu m with a maximal energy output of 450 mW. In a contact focusing application , the absorption depth in water as a function of wavelength was measured. U sing laser parameters, comparable to those used for a pulsed Ho:YAG laser i n contact mode, coagulation spots in human cornea were applied for the cont inuous wave diode laser. RESULTS: The macroscopic and microscopic effects of the diode laser coagula tion on corneas in vitro and in situ were comparable to those of the Ho:YAG laser, if a comparable amount of total energy per spot was applied. CONCLUSION: Due to better optimized laser-collagen interaction, higher corr ections and more stable clinical refractive effects appear achievable using the continuous wave diode laser.