STROMAL THERMAL EFFECTS INDUCED BY NONMECHANICAL (2.94-MU-M) ERBIUM-YAG LASER CORNEAL TREPHINATION

Objective: To determine stromal thermal changes after erbium (Er):YAG laser corneal trephination with the use of 2 open masks. Methods: Corn eal trephination was performed in 89 enucleated pig eyes with an Er:YA G laser (400-microsecond pulse duration), 4 open masks (2 metallic and 2 ceramic) for both donors and recipients, and an automated globe rot ation device. Different combinations of laser settings were used: puls e energy, 100, 200, and 400 mJ; repetition rate, 2 and 5 Hz; and spot size, 1.3 and 3.2 mm. Thermal effects in corneal stroma and regularity of the cut edges were quantitatively assessed by light microscopy, tr ansmission and scanning electron microscopy. Results: Best regularity and minimal thermal effects of the cut were observed with the use of c eramic masks at 200 mJ, 2 Hz, and 3.2-mm spot size, with middepth ther mal changes of 18 +/- 2 mu m. Effects increased with cut depth and wer e lower in donor corneas and with the use of ceramic masks (P<.001). R egularity of the cut was higher in the donors (P=.05) with lower repet ition rates (P<.001). Conclusions: Even with the ''free-running'' Er:Y AG laser mode, features of the trephination cut resembling those creat ed by the 193-nm excimer laser along metal mask were achieved. Ceramic masks may be more suitable than metal masks. The Er:YAG laser seems t o have the potential to be a compact and low-cost alternative in nonme chanical trephination for penetrating keratoplasty. Clinical Relevance : Thermal effects after corneal trephination with the free-running Er: YAG laser (2.94 mm) are limited and predictable.