Stromal Thermal Effects Induced by Nonmechanical (2.94-µm) Erbium:YAG Laser Corneal Trephination

Abstract

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 (400microsecond 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 ther-mal changes of 18 ± 2 µm. Effects increased with cut depth and were lower in donor corneas and with the use of ceramic masks (PϽ.001). Regularity of the cut was higher in the donors (P = .05) with lower repetition rates (PϽ.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.

Thermal load of laser aperture masks in nonmechanical trephination for penetrating keratoplasty with the Er:YAG laser: comparison between stainless steel and ceramic masks

“…This technique has the potential of creating smooth and congruent cut edges in donor and recipient and is a favorable non-contact alternative to mechanical trephination [4,6,7,26,27,30,31] of nonmechanical trephination with the excimer laser, we were looking for an alternative laser system. As shown in other studies [1,8,23], the Er:YAG solid-state laser has potential advantages for corneal incisions or trephination.…”

“…Our solid-state laser based on the active erbium ion that emits at 2.94 µm is attractive because of its low cost, simplicity, and reliability. We demonstrated good efficacy [1,8] in producing corneal incisions, although it has been clear since the first experiments of Seiler et al [22,23] that the quality of corneal ablation for photorefractive procedures suffers from the same limitation (mainly thermal damage) already evidenced with other types of solid-state lasers. Further investigation into suitable selection of the laser operating conditions and special materials for trephination aperture masks may lead to a reduction in this tissue damage.…”

“…First experiments with an Er:YAG laser in a free-running mode [1] gave encouraging results, even though the performance of the ArF laser in terms of precision and minimal extent of thermal damage could not be matched. Clearly, from a technological and clinical point of view, this laser system did not represent an advance over the excimer laser.…”

Corneal shrinkage induced by nonmechanical Q-switched erbium:YAG laser trephination for penetrating keratoplasty in porcine eyes

“…The potential of Er:YAG laser in the free-running mode to replace the 193 nm excimer laser as a more userfriendly and less expensive surgical tool for PK was studied in our department in porcine eyes and human donor corneas [2,3,15]. Pilot studies on a small sample were also published by our group on the effects of Qswitched Er:YAG laser on corneal tissues, showing advantages over free-running Er:YAG laser use, such as lower degrees of thermal damage [44,47,48].…”

“…Mid-infrared lasers have been investigated in the effort to identify a possible replacement for the excimer laser to perform refractive or therapeutic corneal procedures, including PK [1,2,3,4,5,6,8,12,15,20,21,31,33,36,44,46,47,48,49].…”