Femtosecond Laser Keratoplasty

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Zirm performed the first successful human full-thickness corneal transplantation in the early 1900s.1 He performed the surgery without finely gauged needles, sutures, or modern-day viscoelastic devices. In the century that followed, numerous innovations brought penetrating keratoplasty (PKP) procedures to a new level of anatomic and optical success that few surgeons could have imagined. Ramon Castroviejo pioneered the most common PKP technique still in use today by creating a circular corneal button with a circular trephine blade.2,3 Multilevel stepped corneal incisions for improving donor-host alignment and wound stability were introduced initially by Franceschetti and Doret in the 1950s.4 Soon thereafter, Barraquer expanded on this concept and developed a method and special instruments to manually create a “2-level”–shaped incision, with an inner diameter larger than the outer diameter, to preserve greater areas of endothelium in the surgical management of Fuchs’ dystrophy.5,6 The difficulty of this technique prevented widespread adoption. Forty years later, Busin described a “mushroom”-shaped manual PKP technique that also had a stepped incision, but with a smaller inner diameter than outer diameter, a potential advantage for PKP in patients with healthy endothelium that could be retained.7,8 Nevertheless, the challenge of a manually shaped donor and host prevented most surgeons from adopting the shaped incisions, despite the potential improvements in wound integrity and donor-host alignment.The concept of shaped PKP took a major leap forward with the development of the femtosecond (FS) laser for corneal incisions. This technology was first developed as a commercial device in the late 1990s for creation of the corneal flap in laser in situ keratomileusis. The FS laser is an infrared laser that utilizes ultra-short pulses in the range of several hundred FSs. Contiguous pulses are used to create microcavitation bubbles at a precise depth within the cornea—a process called photodisruption. Thermal damage to adjacent tissue in the cornea has been measured to be in the order of 1 μm. The laser spots may be fired in rotating circular pattern that, by translating from deep to superficial and by varying the diameter as the laser translates, can create a wide range of complex incisions that are identical in donor and host corneas. For lamellar dissection, the laser operates at a fixed depth and scans across the cornea in either a raster pattern or a spiral pattern.Historical and Conceptual Background on FS Lasers in OphthalmologyTibor Juhasz, PhD, and his associates designed and constructed the prototype of the ophthalmic FS laser system that became the IntraLase (Abbott Medical Optics, Santa Ana, CA) at the University of Michigan College of Engineering Center for Ultra-fast Optic Sciences in the early 1990s. In collaboration with Ronald Kurtz, MD, and associates from W.K. Kellogg Eye Center, University of Michigan Medical School, the design, development, and analyses of clinical laser parameters followed. In 2002, having relocated to California, Dr Kurtz and associates at the University of California, Irvine undertook in vivo experiments to determine whether the laser (10 kHz) was appropriate for therapeutic corneal applications, particularly for shaped PKP. Their laboratory work demonstrated better wound sealing properties along with less suture-induced astigmatism.9,10 In 2005, US Food and Drugs Administration cleared the use of the FS laser (IntraLase Femtosecond Laser, AMO; Irvine,CA) for laser-enabled full-thickness and partial-thickness corneal incisions, which was rapidly followed by patient treatments at UC Irvine and elsewhere.11–17 At the present time, the new fifth generation IntraLase iFS system (150 kHz) allows for significantly faster laser cutting time with lower pulse energies. Presently several other FS laser platforms have also been modified for laser-enabled keratoplasty.

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