[Refractive surgery].

FEBRUARY 2004 I CATARACT & REFRACTIVE SURGERY TODAY I 27 T he FEMTEC femtosecond (ultrashort pulse) ophthalmic laser (20/10 PERFECT VISION Optische Geräte GmbH, Heidelberg, Germany) is a photodisruptive laser. Although performed since the early 1980s, ophthalmic photodisruption has previously been limited to intraocular procedures because of the relatively large amount of energy needed to initiate laser-induced optical breakdown with the available nanosecond-pulse-duration Nd:YAG lasers. Today, the lower limit of laser pulse duration has decreased by as much as six orders of magnitude to the femtosecond (10-15) range. Photodisruption begins with laser-induced optical breakdown, when a strongly focused and short-duration laser pulse generates a high-intensity electrical field, thereby causing the formation of a mixture of free electrons and ions that constitutes the plasma state. The optically generated hot plasma expands with supersonic velocity and displaces surrounding material. As the plasma’s expansion slows, the initial supersonic displacement propagates through the surrounding tissue as a shock wave. The rapid expansion of the generated plasma quickly decreases its temperature, and the vaporized tissue forms a cavitation gas bubble in the focal volume of the laser beam (Figure 1). The cavitation bubble consists mainly of CO2, N2, and H20, which can diffuse out from the tissue through normal mechanisms. The ablation was found to be nonthermal due to the extremely short interaction time. We clinically evaluated a prototype of the FEMTEC femtosecond ophthalmic laser to create LASIK flaps in a small series of eight eyes. None of these eyes underwent excimer laser ablation treatment thereafter. The mean follow-up period was 1.5 months (ranging from 1 week to 2 months). All of these eyes were scheduled for penetrating keratoplasty at a later date. After the keratoplasty procedure, we further evaluated the corneal buttons by electron microscopy.