Characterization of submicrojoule femtosecond laser corneal tissue dissection

PURPOSE: To document the acute morphologic features of laser of situ keratomileusis (LASIK) flaps created using an IntraLase femtosecond laser (IntraLase, Inc.) with a 60 kHz engine. SETTING: Laser suite in a clinical practice. METHODS: A LASIK flap was created in 4 human eye-bank eyes using the 60 kHz IntraLase femtosecond laser with the following settings: 110 mu m flap thickness, 9.0 mm flap diameter, 60-degree hinge length, 65-degree side cut, 0.4 mu J or 0.7 mu J raster energy, 7 mu m x 7 mu m or 9 mu m x 9 mu m spot/ line separation, and 1 mu J side-cut energy. Immediately after the laser pass and without the flap being lifted, the globes were placed in fixative and subsequently processed for light and transmission electron microscopy. RESULTS: All 4 procedures were completed without complications or the appearance of an opaque bubble layer. The flaps were of uniform thickness and equaled the attempted thickness. Some areas had a complete dissection; other areas had scattered, incomplete tissue bridges. The adjacent corneal stroma and keratocytes were uninjured. When the epithelium was removed, the stromal component of the flap was measured as the attempted thickness; when the epithelium was present, the total flap thickness approximated the attempted flap thickness. CONCLUSIONS: Laser in situ keratomileusis flaps were safely created using raster energies and laser spot separations below those being used clinically. This technique may allow creation of flaps that are reproducibly thinner than those currently being performed and thus confer the benefits of surface ablation and LASIK.