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B. Seitz, A. Langenbucher, C. Hofmann-Rummelt, U. Schlötzer-Schrehardt, G.O. Naumann; Nonmechanical Posterior Lamellar Keratoplasty Using a Femtosecond Laser (Femto-PLAK) for Corneal Endothelial Decompensation . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4699.
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Purpose: Since manual lamellar dissection is still technically very demanding in posterior lamellar keratoplasty, the purpose of this study was to assess the potential of a short pulsed laser to cut a posterior graft and bed in a controlled automated manner. Material and Methods: In this laboratory study 18 freshly enucleated porcine eyes and 10 human donor corneas not suitable for corneal transplantation were treated. Using the laser FEMTEC (20/10 PERFECT VISION, Heidelberg, Germany) we performed posterior lamellar dissections in the whole eye (wave length ~1 µm, pulse energy <10 µJ, spot size <10 µm, repetition rate 12.5 kHz) starting from the anterior chamber and finalizing with the lamellar bed. Pulse energy and spacing of the spots were varied. Following the laser action complete flaps (6 to 7 mm diameter) were either removed manually or left in situ and were fixed in 10% buffered formaldehyde solution and processed for PAS/HE light microscopy, transmission (TEM) and scanning (SEM) electron microscopy. Main outcome measures included (1) feasibility of the flap creation, (2) configuration of the flap/bed, (3) regularity of the cut surfaces, (4) thermal damage adjacent to the cut edge. Results: Applying appropriate combinations of pulse energy and spacing, successful creation of the flaps took between 31 and 90 s. Most flaps were removed easily manually immediately after laser trephination. Thickness of different homogeneous flaps/beds with rectangular borders could be varied between 50 and 500 µm. Before removal, flaps were delineated by partly confluent gas bubbles (max. 2 mm long) with minute tissue bridges (typically 5 to 10 µm) in between. SEM displayed smooth cut surfaces and rectangular corners with minor remaining tissue bridges (~5 µm). By TEM, the cut edges were lined by a delicate, electron-dense layer (5 to 10 nm in width) and essentially normal adjacent collagen fibers without any evidence of thermal damage. Conclusions: Femtosecond laser technology seems to offer a promising approach towards minimally invasive posterior lamellar keratoplasty (femto-PLAK) via small tunnel incisions to avoid high postkeratoplasty astigmatism in corneal endothelial diseases. Further studies have to focus on the corneal endothelial changes in very thin lamellar grafts.
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