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Five femtosecond lasers are now commercially available. They vary in their features and capabilities, but the product category as a whole is characterized by a rapid evolution toward improved technology with more changes and a growing list of uses expected in the future.
"My charge today was to speak about where we are going with the femtosecond laser," said Dr. Binder, a private practitioner in San Diego. "Looking at the past and the present, it is clear that significant progress has already been made, and I would predict that in the years ahead, mechanical microkeratomes will go the way of the dinosaurs."
Beginning with a brief overview of four femtosecond lasers (IntraLase, Advanced Medical Optics; Femtec, 20/10 Perfect Vision; VisuMax, Carl Zeiss Meditec; and Femto LDV, Ziemer), he highlighted the key features of the devices as well as how they differ. A new femtosecond laser from Wavelight was introduced during the meeting, but the particular aspects of the laser were not presented by Dr. Binder or in other formal lectures.
The lasers also are differentiated by the way they deliver energy to the eye, Dr. Binder said. The IntraLase uses a raster to make the cut, the Femtec spirals out to in, the VisuMax spirals in to out, and the Femto LDV overlays spots by about 50%.
Another difference relates to the methods used for achieving thickness settings and the variability in achievable thickness. With the Femto LDV, thickness is adjusted using mechanical spacers (foils) and the resectable thickness choices are fixed. Each of the other three devices uses software control, but the current generation IntraLase and Femtec can create flap thicknesses from 90 to 400 µm.
Centration of the surgical procedure also is controlled by the computer using the IntraLase, whereas it is done mechanically with the handpiece on the Femto LDV and mechanically with the VisuMax and Femtec. He said that although mobility and spot overlap control are current features of only the Femto LDV, it also is the only device that requires application of a masking fluid to connect the applanation device to the patient's cornea.
"It should be mentioned that a thick viscous fluid placed on the cornea before applanation adds some thickness that can throw off the precision of the instrument's flap measurements and adds potential for vertical gas breakthrough," Dr. Binder said.
Current and future applications
Uses of the femtosecond laser are rapidly expanding beyond LASIK flap creation. Applications vary by instrument, but considering the entire category, they are being used to create channels for intracorneal ring segments or intrastromal pockets and to perform astigmatic keratotomy, penetrating keratoplasty with perpendicular wounds, a shaped keratoplasty (Intralase-enabled keratoplasty), and lamellar keratoplasty. In addition, femtosecond lasers can be implemented for corneal biopsy, tattooing, stem cell transplants, presbyopic surgery, and for the femtosecond lenticule extraction (FLEX) procedure for myopia, he said.
New applications are expected to include photodisruption of the crystalline lens as a method to treat presbyopia (increasing lens flexibility for accommodation) or for softening the lens to enable extraction through a very small hole in the lens capsule, Dr. Binder said. The femtosecond laser also may be used for capsule surgery, and it has potential application in glaucoma management, in which it can be used for scleral procedures or to facilitate filtration by "cleaning out" Schlemm's canal via a reverse "blow out" of gas from the anterior chamber through the canal.
"With the second harmonic wave of these lasers, we also anticipate applications in pathology diagnostics in vivo and expansion of their use for dermatology applications," he said.
The instruments themselves will be modified in more ways as well, according to Dr. Binder. Newer lasers will have smaller footprints and be more mobile, and some will be physically combined within the chassis of the excimer laser. Options for surgeon control over laser parameters also will increase as will speed.
"Increased speed will enable greater variation in spot size and line separation, smoother lifts and beds, thinner flaps because of less energy, and perhaps the benefit of a decreased risk of vertical gas breakthrough," he concluded.