Stromal thermal effects induced by nonmechanical (2.94-μm) 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: Corneal trephination was performed in 89 enucleated pig eyes with an Er:YAG laser (400-microsecond pulse duration), 4 open masks (2 metallic and 2 ceramic) for both donors and recipients, and an automated globe rotation device. Different combinations of laser settings were used: pulse 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, transmission and scanning electron microscopy. Results: Best regularity and minimal thermal effects of the cut were observed with the use of ceramic masks at 200 mJ, 2 Hz, and 3.2-mm spot size, with middepth thermal changes of 18 +/- 2 mu m. Effects increased with cut depth and were lower in donor corneas and with the use of ceramic masks (P<.001). Regularity of the cut was higher in the donors (P=.05) with lower repetition rates (P<.001). Conclusions: Even with the "free-running" Er:YAG laser mode, features of the trephination cut resembling those created 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 to have the potential to be a compact and low-cost alternative in nonmechanical 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.