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B. Seitz, H. Brünner, A. Viestenz, C. Hofmann–Rummelt, A. Langenbucher; Inverse mushroom–shaped nonmechanical penetrating keratoplasty using a femtosecond laser . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2923.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The optimal penetrating keratoplasty procedure consisted of a nonmechanical trephination creating a self–sealing donor/host apposition. The purpose of this study was to demonstrate the feasibility of an inverse mushroom–shaped corneal trephination using a femtosecond laser in a non–contact automated manner. Material and Methods: In this laboratory study 10 PMMA blocks and 7 rabbit corneas were treated with a commercially available femtosecond laser source (Ti:Sapphire Amplifier Laser System, type "Hurricane–i" – kindly provided by Spectra–Physics), which was adapted to a rapid beam delivery system (wave length 800 nm, pulse energy 2 to 20 µJ, repetition rate 5 kHz, pulse length 150 to 400 fs). All electronic components were custom–made or specially modified for this system. The beam was expanded to the maximum aperture of the mirror (20 mm) and finally focussed onto the target by means of a f–theta 100 mm telecentric lens assembly. The trephination profile consisted of (1) a 7 or 6 mm diameter cylinder from the anterior chamber, (2) an intermediate horizontal plane inwards in the mid–stroma and, finally, (3) a concentric 5 mm diameter cylinder upwards beyond the epithelium. Following the laser action PMMA blocks were examined by a transmission microscope and corneas were fixed in 10% buffered formaldehyde solution and processed for PAS light microscopy. Results: Applying appropriate combinations of pulse energy and spacing, creation of inverse mushroom–shaped trephinations took less than 60 s. In PMMA blocks, the thickness of the outer (stipe) and inner part (cap) of the "inverse mushroom" could be varied. Histology in rabbit eyes displayed trephination edges delineated by partly confluent gas bubbles (10 to 40 microns) with tissue bridges in between. Conclusions: Femtosecond laser technology seems to offer a promising approach towards minimally invasive self–sealing "no–stitch keratoplasty". In contrast to other systems currently available, our approach favors non–contact (!) application which seems to be indispensable for penetrating keratoplasty in corneas with irregular curvatures such as keratoconus. Further studies have to focus on the improvement of the laser setup.
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