Carlos G. Suarez

Femtosecond Laser Flap Creation for Laser in situ Keratomileusis: Six-month Follow-up of Initial U.S. Clinical Series

PURPOSE To evaluate clinical performance of a femtosecond laser for flap creation in laser in situ keratomileusis (LASIK). METHODS A prospective, consecutive series of 208 eyes (122 patients) undergoing LASIK between June 2000 and November 2000 using a femtosecond laser for creation of the corneal flap were evaluated for the incidence of complications. A subset of 114 patients who underwent myopic procedures and who were followed for 6 months was analyzed using standard outcome measures. RESULTS In 4 of 208 eyes (1.9%), suction was lost during the procedure, causing the flap resection to be interrupted. However, in all four of these eyes the procedure was successfully performed 5 to 45 minutes after re-applanation of the eye. No postoperative complications or adverse events were observed in any treated eye. In the subgroup of 96 eyes undergoing plano correction and followed for 6 months (preoperative spherical equivalent refraction range -0.63 to -12.40 D), 98% (94 eyes) achieved uncorrected visual acuity of 20/40 or better; 94% (90 eyes) achieved 20/30 or better, 79% (76 eyes) achieved 20/25; and 55% (53 eyes) achieved 20/20 or better--all without benefit of retreatment. CONCLUSION Femtosecond laser corneal flap creation is a safe and effective alternative to traditional mechanical microkeratomes. Standard LASIK nomograms appeared to apply equally well to the all-laser LASIK procedures. The potential for improved flap safety, reproducibility, flexibility, as well as for additional corneal applications are now being explored.

FEMTOSECOND LASER HEATING OF MULTI-LAYER METALS. II: EXPERIMENTS

Abstract Femtosecond thermoreflectivity experiments are performed to investigate energy deposition and transport during the very early period of short-pulsed laser heating of gold and chromium multi-layer metal films. The chromium layer underneath the top gold layer is found to produce significant effects on the laser-energy deposition process. Experimental results show that radiation absorption by free electrons and the subsequent heating of the lattice occur not only at different times but also at different locations in a multi-layer metal film. The conventional radiation heating model fails to predict these results, and a more rigorous two-step model agrees well with the measured data.

Shock wave and cavitation bubble dynamics during photodisruption in ocular media and their dependence on the pulse duration

Shock waves and cavitation bubbles generated by optical breakdown may strongly influence the surgical effect of photodisruptive lasers. We have investigated the shock wave and cavitation bubble effects of femtosecond and picosecond laser pulses generated during photodisruption in corneal tissue and water. Laser pulses with 150 fs duration at approximately 620 nm wavelength have been focused into both corneal tissue and water to create optical breakdown. Pulses with durations of 20 ps have been applied for comparative studies. Time-resolved flash photography has been used to investigate the dynamics of the generated shock waves and cavitation bubbles. Femtosecond pulse engender rapidly decaying shock waves in both materials. The spatial range of shock waves induced by femtosecond laser pulses is considerably smaller than that of shock waves induced by picosecond optical breakdown. Cavitation bubbles excited by femtosecond pulses are observed to develop more rapidly and to reach smaller maximum diameter than those generated by longer pulses. In corneal tissue intrastromal cavitation bubbles generated by femtosecond pulses disappear within a few tens of seconds, notably faster than cavitation bubbles generated by picosecond pulses. The reduced shock wave and cavitation bubble effects of the femtosecond laser result in more localized tissue damage. Therefore, a more confined surgical effect should be expected from a femtosecond laser than that from picosecond (or nanosecond) lasers. This indicates a potential benefit from the application of femtosecond laser technology to intraocular microsurgery.

The Femtosecond Blade: Applications in Corneal Surgery

Surgeons use a number of devices to create incisions in tissue. These include steel and gem blades, radio frequency, high-pressure waterjet, and electrocautery technologies. Interestingly, while lasers have an established place in the operating room, as cutting tools they play a minor role. Until recently, a major limiting factor was the lack of three-dimensional precision found with each of three types of laser-tissue interaction: photocoagulation, photoablation, and photodisruption.

Clinical analysis of the neodymium:YLF picosecond laser as a microkeratome for laser in situ keratomileusis : Partially sighted eye study

Purpose: To evaluate the use of a picosecond neodymium:YLF (Nd:YLF) laser as a nonmechanical intrastromal microkeratome. Setting: Universita Cattolica del Sacro Cuore, Rome, Italy. Methods: An intrastromal spiral disc pattern of picosecond laser pulses was used to create a corneal flap for laser in situ keratomileusis (LASIK) in 14 partially sighted eyes. Results: Flaps with a 6.0 mm diameter and 180 to 200 urn depth were successfully created in most cases. The underlying stroma was treated with a Lambda Physik excimer laser using a 3.5 to 4.5 mm optical zone. Patients were divided into 3 groups for target corrections of 5.0, 10.0, and 15.0 diopters of myopia. Good corneal clarity and refractive undercorrection were recorded in each group 6 months postoperatively. The undercorrection was due in part to the limited optical zone of the laser’s delivery system. Some flap decentration was noted. Conclusion: This pilot study indicates that the Nd:YLF picosecond laser may be clinically applied for creating corneal flaps for LASIK. Further refinements of the laser delivery system will include enlargement of the flap diameter and improvements in flap centration. The use of a femtosecond laser may expand the capabilities and precision of this technology.

Ophthalmic applications of ultrashort pulsed lasers

Ultrashort laser pulses can be used to create high precision incision in transparent and translucent tissue with minimal damage to adjacent tissue. These performance characteristics meet important surgical requirements in ophthalmology, where femtosecond laser flap creation is becoming a widely used refractive surgery procedure. We summarize clinical findings with femtosecond laser flaps as well as early experiments with other corneal surgical procedures such as corneal transplants. We also review laser-tissue interaction studies in the human sclera and their consequences for the treatment of glaucoma.

Femtosecond laser eye surgery: the first clinical experience

A brief review of commercial applications of femtosecond lasers in a clinical setting with emphasis on applications to corneal surgery is presented. The first clinical results of 208 procedures conducted from June to November 2000 is reported. The results show that femtosecond lasers may be safely used as keratome for use in LASIK procedures.

Imaging through quasi-particle transport

Quasi-particles travel down a one-dimensional concentration gradient in a thin metallic film composed of regions of only gold and regions of gold-titanium-gold multilayers. We obtain an image depending on whether the quasi-particles encounter a multilayer.

Quasi-electron and phonon interactions in the femtosecond time domain

Abstract The properties of optically excited particles in ultra thin metallic films differ markedly between the femto, and the picosecond time domain. In the specific case of Au films, the difference arises from the lack of thermal equilibrium in the femtosecond domain. It is also observed that some quasi-particles travel essentially unhindered, i.e., ballistically at near the Fermi velocity. It is further concluded that although a large number of phonons are produced through the decay of electrons, only a small fraction of the phonon energy returns to the quasi-electrons. It is further demonstrated that the experimental results are not consistent with the so-called “two temperature model (TTM)”, and that an attempt to use classical thermal dynamics, when a system is not in thermal equilibrium, is difficult to justify. We demonstrate that excellent agreement exists between experiment and Fermi-liquid theory (FLT), and that many parameters and functional relations, which describe quasiparticle dynamics and transport, can be recovered by the application of FLT to the experimental results.