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P. Pogorelov, M. Pollhammer, C. Rössler, U. Schlötzer-Schrehardt, C. Rummelt, C. Cursiefen, F. E. Kruse; Experimental Femtosecond Laser-Assisted "Big Bubble" Deep Anterior Lamellar Keratoplasty (DALK). Invest. Ophthalmol. Vis. Sci. 2009;50(13):1239.
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The major factor infuencing DALK surgery is the exact (predescemetal) position of the needle, which allows separation of Descemet’s membrane from corneal stroma. Here we investigate the reproducibility of intrastromal tunnels, which serve to precisely position the needle during DALK surgery.
Intrastromal tunnels were created in rabbit eyes using a 40 kHz femtosecond laser workstation (Femtec, 20/10 Perfect Vision AG, Heidelberg, Germany). Preoperative pachymetry was obtained using Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany). Depth was set between 80% and 95% of corneal thickness. Using an energy of 2500 µJ, tunnels with an opening of 940 µm originating from the corneal surface were created at an angle of 60°, extending to a depth between 320 µm and 380 µm. Postoperatively, eyes were analyzed by slit lamp OCT (SL-OCT, Heidelberg Engineering GmbH, Heidelberg, Germany), conventional and electron microscopy.
Tunnels were complete and allowed insertion of the needle for air delivery. In histology there was no visible alteration of tunnel walls. Selected depth of 95% of corneal thickness (380 µm) resulted in perforation of Descemet’s membrane in 4 of 5 eyes. Depth between 80 and 90% showed intact posterior stroma and Descemet’s membrane. Tunnel depth on histological sections correlated well with pachymetry data (r=0.85) in all eyes.
In contrast to manual dissection or trephination with semi automated methods, femtosecond laser allows for precise, predescemetal creation of a tunnel to deliver air to the posterior stroma, thus improving the safety of DALK surgery.
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