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Femtosecond Laser-Assisted Corneal Flap Cuts: Morphology, Accuracy, and Histopathology

From the Heidelberg Intraocular Lenses and Refractive Surgery Research Group, Department of Ophthalmology, Ruprecht-Karls-University of Heidelberg, Heidelberg, Germany.

PURPOSE. Precision in corneal flap cutting is essential in LASIK surgery. Current mechanical microkeratomes have a very good performance record; however, in a few cases, complications can occur during the microkeratome pass and flap cut. Femtosecond lasers offer an alternative to the mechanical cut and can provide additional features regarding the flap morphology. In this study, we analyzed femtosecond laser flaps regarding their morphology, cut accuracy, and histopathology.

METHODS. Forty-five fresh porcine cadaveric eyes were prepared for femtosecond laser flap cutting with the Femtec femtosecond laser system (20/10 Perfect Vision, Heidelberg, Germany). The eyes were assigned to three different thickness groups, with 120-, 140-, or 180-µm cut depth, respectively. In addition, different flap diameters ranging from 8.0 to 9.5 mm and rim edge angulations between 60 ° and 90° were performed. After the cut, the eyes were examined under a microscope regarding accuracy and potential defects, and flap thickness and diameter were measured. In addition, flaps were prepared for further histopathologic examination.

RESULTS. All flap cuts were easily performed without any intraoperative complications. Flap thickness measurements revealed a median (in micrometers) of 110.5 (intended thickness 120), 142.5 (intended 140), and 180.0 (intended 180), respectively. The flap diameter for an intended size between 8.0 and 9.5 mm was within a range of ±0.4 mm, the median at the maximum was 0.3 mm off. Histopathology revealed very low to almost no changes in the stromal structure of the cornea and correct hinge angulations.

CONCLUSIONS. LASIK flap cuts were easily performed without any complications. The accuracy and morphology were very precise and consistent. Histopathology revealed a smooth cut with hinge angulations, as expected.