Intrastromal laser in situ keratomileusis with a picosecond Nd:YLF laser

Purpose. Laser in situ keratomileusis (LASIK) requires a microkeratome to generate an anterior corneal flap, plus an excimer laser to ablate the underlying stromal tissue. Herein we introduce the concept of intrastromal LASIK performed with a single laser system. Methods. A neodymiumdoped yttrium-lithium-fluoride (Nd:YLF) laser with a plano-plano quartz applanation lens was used to generate various patterns of intrastromal photodisruption in human donor eyes. Results. Smooth intrastromal dissections, 6mm in diameter, were generated 160μm below the corneal surface when the laser delivered pulses at 1kHz with energies of either 40μJ/pulse or 60μJ/pulse, placed 20μm apart in an expanding spiral. This enabled us to fashion corneal flaps for LASIK. The ease of the surgery and quality of the dissection corresponded well, and it was evident that both deteriorated noticeably when the laser pulses were separated by 25μm or 30μm, regardless of pulse energy. Using 40μJ laser pulses placed 20μ apart we created a 5mm diameter, 290μm thick (160μm-450μm), plano-convex stromal lenticule below a corneal flap that was easily extracted when the flap was raised. Conclusions. Intrastromal LASIK with a Nd:YLF laser could offer a favorable alternative to LASIK performed with a microkeratome and an excimer laser.