Just a little more than 10 years have passed since the femtosecond laser was first used to create a LASIK flap. Now, the laser can be applied across the entire spectrum of corneal surgery, including therapeutic corneal treatments, intrastromal femtosecond laser incisions, and intrastromal refractive correction. This device has also found application in cataract surgery. In collaboration with Gerd U. Auffarth, MD; Josef F. Bille, PhD; G.I.W. Duncker, MD; Kristian Hohla, PhD; Mike P. Holzer, MD; Laszlo Kiraly, MD; Michael C. Knorz, MD; Georg Korn, PhD; Frieder H. Loesel, PhD; Udo Ludwig, Dipl Ing; Tobias H. Neuhann, MD; and Anna Sasse, MD, I recently wrote a book reviewing femtosecond laser technology and its applications.1
This compilation provides an introduction and historical overview; lays out the physical principles of the generation and amplification of ultrashort laser pulses; explains laser-tissue interaction, multiphoton imaging, and biomechanical modeling of the femtosecond laser; describes the clinical applications; discusses refractive surgery techniques with the femtosecond laser; and explores prospects for future use.
USE IN OPHTHALMOLOGY
Laser is an acronym for light amplification of stimulated
emission of radiation. As such, it is a novel source of radiation
that has been used for a wide range of purposes,
from scanning barcodes and entertainment technology
(eg, CD players) to medical applications. Its use in ophthalmology
is straightforward, mainly because the
human eye is one of the most accessible organs.
Furthermore, the transparency of the eye allows easy
diagnostics and treatment throughout the entire globe.
Following on the use of excimer lasers to ablate corneal tissue, femtosecond lasers were introduced to provide ultra-precise intrastromal tissue manipulation and ablation. LASIK flap cuts and intrastromal refractive procedures with this technology utilize the properties of laser-tissue interaction to achieve optimal results and increase procedural safety. Today, the breadth of intrastromal treatments possible with the femtosecond laser include mechanical tunnel incisions for implantation of intrastromal corneal ring segments (ICRS), penetrating keratoplasty (PKP), anterior lamellar keratoplasty (ALK), posterior lamellar keratoplasty, and astigmatic keratotomy.
CORNEAL TREATMENT BENEFITS
Depending on the corneal treatment, the femtosecond
laser has many clinical advantages. In
patients with keratoconus, the femtosecond laser is
beneficial because it is not always possible to employ
mechanical cutting techniques. The laser allows personalization
of the tunnel depth, width, and total
diameter for ICRS placement and has led to the
development of new geometric graft shapes for use in PKPs. It also permits a variety of incision angles
and diameters for treatment.
Another advantage of the femtosecond laser is that it creates a precisely defined graft thickness (up to 400 μm) for ALK treatments, meaning the surgeon can apply an individualized approach to each treatment. During endothelial transplantation with the femtosecond laser, no suture is needed, which decreases the amount of induced astigmatism. (The drawbacks are that the maximum permissible depth value is 400 μm, and that for this treatment to be beneficial with the femtosecond laser, preoperative diagnostics must be more precise.) Femtosecond ALK is a possible treatment for high degrees of astigmatism when LASIK, LASEK, or phakic IOLs are contraindicated.
REFRACTIVE TREATMENT BENEFITS
Refractive treatments performed in part with the
femtosecond laser have come a long way since the initial
10-kHz models. When used for creating the LASIK
flap, these early lasers would leave tissue bridges, which
required significant time and manipulation to separate,
often caused clinically significant corneal edema, and in
some cases resulted in poor visual results. Later and current
generations of the femtosecond laser achieve
smoother flap beds, induce faster healing, and generate
better postoperative vision.
The benefits of using the femtosecond laser for the creation of LASIK flaps are numerous. First, the hinge position, length, diameter, and thickness of the flap are precise and can be individualized depending on the treatment. Second, the geometry of the sidecut can be created at different angles, corresponding to the patient interface. Third, there is full visual control during the entire procedure. Fourth, intraoperative complications are rare.
OUTLOOK
The femtosecond laser has already given rise to high-performance techniques in ophthalmology;
however, we are optimistically awaiting the development
of future applications. For starters, femtosecond-
assisted cataract surgery is on the brink of
acceptance, with several surgeons now testing its
safety and effectiveness. (See New Generation of
Femtosecond Lasers Emerges, page 55.) Furthermore,
another potential application for the femtosecond
laser is creating thin canals to prevent extensive
intraocular pressure in glaucoma patients. (However,
this would require alteration of the direction of the
laser beam using mirrors.)
Femtosecond platforms are also beginning to integrate diagnostic technologies into their systems to measure the patient's eye directly under the device. This software records essential corneal parameters, including corneal thickness, while the eye is docked so that treatment occurs only in the intended area. Further development in this area may facilitate customized incision placement and geometry as well as direct monitoring of the ablation response.
CONCLUSION
The maturation of ultra-fast laser technology—the
femtosecond laser—has increased the capacity at
which ophthalmologists can treat patients. With
today's wavefront-based customized procedures, this
combination should yield results closer to the supernormal
vision patients so desperately want. As surgeons,
our main task will be to adapt surgical procedures
to femtosecond technology so that we can
achieve its maximum benefit in as many treatments as
possible.
Mark Tomalla, MD, practices at the Clinic Niederrhein, Clinic for Refractive and Ophthalmic Surgery, Duisburg, Germany. Dr. Tomalla states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +49 203 5081711; fax: +49 203 5081713; e-mail: mark.tomalla@ejk.de.
