Infrared laser surgery of the cornea. Studies with a Raman-shifted neodymium:YAG laser at 2.80 and 2.92 micron.

Tissue absorption lengths for infrared radiation at 2.8 to 3.1 micron are very short due to strong absorption by water. Corneal ablation using pulsed lasers at these wavelengths can potentially produce incisions similar in quality to cuts produced by excimer lasers at 193 nm. The authors have used 8-ns pulses at 2.80 and 2.92 micron, generated by a Raman-shifted neodymium:YAG (Nd:YAG) laser, to make slit-like incisions in bovine and human corneas. At 2.8 micron, etch depth per pulse increases sigmoidally from 0.15 micron at 390 mJ/cm2 to 3.8 micron at 2200 mJ/cm2. No ablation occurs at fluences below 250 mJ/cm2. Light and transmission electron microscopy show smooth-walled incisions bordered by a thermally damaged region that varies in width from 1.5 micron at 600 mJ/cm2 to 10 micron at 2200 mJ/cm2. The small amount of tissue damage produced at low fluences suggests that infrared ablation may be useful in keratorefractive surgery.