Scanning electron microscopic characteristics of lamellar keratotomies using the Femtec femtosecond laser and the Zyoptix XP microkeratome. A comparison of quality

OBJECTIVE: To demonstrate the qualities and compare the typical features of cut surfaces and cut edges created by the Femtec femtosecond laser and the Zyoptix XP microkeratome, using scanning electron microscope (SEM) pictures. METHODS: Lamellar keratotomies were performed using a femtosecond laser (40 kHz) or a microkeratome on freshly enucleated porcine eyes (n=16, eight each per technique). After special preparation, SEM images were taken to evaluate the qualities of the cut surfaces and cut edges. Therefore, special criteria were involved, including relief and homogeneity of the surface and sharpness of the cut edges. RESULTS: Surfaces created by microkeratome cuts were very homogenous. Concerning surface relief, nearly no irregularities occurred. Cut edges showed a flat, serrated course from the epithelial layer to the stroma of the cornea. The edges were sharp and easily visible. After preparation using the femtolaser, the surface showed many rips in the tissue, leading to irregularities. Nevertheless, the cut edges were very sharp and entered the corneal layer straight at 90 degrees . CONCLUSIONS: A comparison of the two systems shows that the microkeratome creates a more homogenous cut surface. The need for preparation after automated cutting with the femtosecond laser leads to irregularities on the cut surface. The cut edges of both systems tested here differ concerning their angles on entering the tissue. With regard to the sharpness of the cuts, the qualitative aspect is nearly similar, although the cut edges of the microkeratome are serrated. Because the microkeratome-cut edge has a flatter course, the wound area might be bigger. Cut edges with the steepness produced by the femtosecond laser could be an advantage for repositioning the flap after LASIK. If excimer laser ablation is performed later, the flap bed created by the femtosecond laser could be disadvantageous.