Abstract
A recent study showed that 355-nm nanosecond lasers cut cornea with similar precision to infrared femtosecond lasers. However, use of ultraviolet wavelength requires precise assessment of ocular safety to determine the range of possible ophthalmic applications. In this study, the 355-nm nanosecond laser was evaluated for corneal and iris damage in rabbit, porcine, and human donor eyes as determined by minimum visible lesion (MVL) observation, live/dead staining of the endothelium, and apoptosis assay. Single-pulse damage to the iris was evaluated on porcine eyes using live/dead staining. In live rabbits, the cumulative median effective dose (ED50) for corneal damage was 231 J/cm2, as seen by lesion observation. Appearance of endothelial damage in live/dead staining or apoptosis occurred at higher radiant exposure of 287 J/cm2. On enucleated rabbit and porcine corneas, ED50 was 87 and 52 J/cm2, respectively, by MVL, and 241 and 160 J/cm2 for endothelial damage. In human eyes, ED50 for MVL was 110 J/cm2 and endothelial damage at 453 J/cm2. Single-pulse iris damage occurred at ED 50 of 208 mJ/cm2. These values determine the energy permitted for surgical patterns and can guide development of ophthalmic laser systems. Lower damage threshold in corneas of enucleated eyes versus live rabbits is noted for future safety evaluation.
Highlights
Laser-assisted in situ keratomileusis (LASIK) is the most common refractive surgery in the United States, with over 600,000 procedures/year
The first step in LASIK is the cutting of a thin corneal flap, which is peeled back to expose the stroma for reshaping by excimer laser ablation
Endothelial damage was determined after staining with live/ dead fluorescent assay in which live cells are labeled with a cytoplasmic green fluorescent dye and dead cells are labeled with red fluorescent dye (EthD-III) in the nuclei
Summary
Laser-assisted in situ keratomileusis (LASIK) is the most common refractive surgery in the United States, with over 600,000 procedures/year. The first step in LASIK is the cutting of a thin corneal flap, which is peeled back to expose the stroma for reshaping by excimer laser ablation. Mechanical microkeratomes were used to create the corneal flap but infrared femtosecond laser systems,[1] which can cut thinner, more precise, and customizable flaps,[2] were soon developed. Despite the increased cost compared to microkeratomes, femtosecond laser systems have become the most common choice for corneal flap creation.[3]. A promising new laser system for corneal flap cutting that uses a subnanosecond microchip ultraviolet (UV) laser has been demonstrated.[4,5] The simpler design of the 355-nm laser offers a much more compact, inexpensive, and precise flap cutter than is possible with current femtosecond lasers. The 2013 study by Trost et al.[4] showed that 6.5-mm diameter corneal flaps could be created in rabbits with no unintended UV-induced damage to the cornea at a total radiant exposure of 6.9 J∕cm[2], it did not establish an operational
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