Free-running erbium : YAG laser for nonmechanical trephination in penetrating keratoplasty: first results of experimental trephination of human donorcorneas

Background: A study was carried out to evaluate the potential suitability o f a free-running erbium:YAG 2.94-mu m laser for trephination of human corne as in penetrating keratoplasty. Methods: Two human donor corneas were place d in an artificial anterior chamber and moved with an automated rotation de vice (one rotation per minute). An erbium:YAG laser beam (pulse duration 40 0 mu s, repetition rate 2/s, energy density 2.5 and 15.0 J/cm(2)) was focus ed on the outer edge of a round ceramic mask placed on the human donor corn eas for ablation of tissue. Results: With a fluence of 15.0 J/cm(2), perfor ation was achieved after 500 pulses. Perpendicular central cut edges with m ild stromal ridges and, by light microscopy, a 12 to 45-mu m area of stroma l thermal effects and focal endothelial changes up to 200 mu m central to t rephination were observed. Conclusions: The erbium:YAG laser could be a pro mising "low-cost alternative" to the excimer laser for nonmechanical trephi nation in penetrating keratoplasty. Further studies will have to focus on r eduction of thermal damage and on wound healing.