Limitations of erbium:YAG laser photorefractive keratectomy.

Abstract

The erbium:YAG laser (lambda = 2.94 microm) has been considered promising as an alternative to the ArF excimer laser in photorefractive keratectomy (PRK). However, corneal application of this mid-infrared solid state laser is still plagued with various disadvantages compared to that of the ArF excimer laser (lambda = 193 nm). We discuss the limitations of PRK with the erbium:YAG laser. Measurements of ablation threshold, ablation efficiency, and thermal damage were done to compare the process of erbium:YAG laser photoevaporization to the ArF excimer laser. PRK procedures were performed on fresh enucleated pig corneas to investigate the morphology and surface roughness of the cornea after scanning-spot and fundamental mode photoablation. Surface roughness was measured by using a tactile surface reprofiling system. The ablation threshold and the ablation efficiencies for the erbium:YAG laser are significantly higher compared to the ArF excimer laser. Collateral thermal damage decreases with a reduction of laser pulse duration to a minimum of approximately 5 microm. Scanning electron microscopy and surface roughness measurements of the corneal surface after erbium:YAG laser treatment demonstrated higher surface roughness compared to ArF excimer laser treatments. The erbium:YAG laser is not at present an alternative to the ArF excimer laser for photorefractive keratectomy.