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Surgeon reviews features of femtosecond lasers for LASIK
The newer-generation lasers vary in speed, vacuum level, visualization and spherical contact interface.
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 Sonia H. Yoo |
Based on an evaluation of commercially available femtosecond lasers in the U.S., the future for LASIK seems promising.
“Improvement in LASIK flaps will result in better safety and visual outcomes,” Sonia H. Yoo, MD, said at OSN New York 2011.
Dr. Yoo discussed five femtosecond lasers that are used for refractive surgery: IntraLase (Abbott Medical Optics), Femtec (Technolas Perfect Vision), VisuMax (Carl Zeiss Meditec), Femto LDV (Ziemer) and WaveLight FS200 (Alcon).
“All of these lasers work in the near-infrared region, have very small spot sizes and high repetition rates,” Dr. Yoo said. The energy per pulse for the devices is small, in the microjoule or nanojoule range.
The platforms differ in the speed of their lamellar cuts, but all are fast.
Advantages
There are several benefits to using femtosecond lasers for LASIK.
“We can start to customize the geometry of the LASIK flaps. This might be advantageous for particular patients that require thinner flaps or might require a slightly more oval flap if they have high astigmatism,” Dr. Yoo said.
As opposed to a microkeratome, a femtosecond laser allows for customizable LASIK flaps for depth, diameter, hinge angle, hinge position and side-cut angle.
“A given individual might come in with a pannus or a nasal pterygium, for which you might want to shift the hinge angle superiorly to avoid cutting through corneal vessels,” Dr. Yoo said. “This is very helpful.”
There was debate regarding earlier-generation femtosecond lasers as to whether their stromal beds were as smooth as microkeratome beds.
“But I would argue that with the newest generation of femtosecond lasers, we are able to achieve very smooth cuts compared to the microkeratome,” Dr. Yoo said. “Perhaps more important, though, is the data looking at the higher reproducibility and lower re-treatment rates with femtosecond laser flaps vs. microkeratome flaps.”
This may be attributable not only to the flap quality, but also to the fact that the femtosecond laser creates uniformly dry stromal beds compared with microkeratome flaps, which are variably hydrated.
Additionally, most of the newer femtosecond lasers allow surgeons to see what they plan to cut before they actually make a cut, which is an advantage over microkeratomes, Dr. Yoo said.
The Femto-LDV has a very small footprint, Dr. Yoo said, which may benefit practices that want to move a laser between suites or rooms.
Features of the lasers
All the evaluated femtosecond lasers have a lower vacuum than a microkeratome. The WaveLight FS200 and Intra-Lase have relatively higher vacuum, Dr. Yoo said, while the VisuMax and Femtec have lower vacuum.
“Patients treated on low vacuum lasers typically do not lose vision during the treatment,” she said.
The VisuMax and Femtec have spherical contact interfaces, while the IntraLase, WaveLight FS200 and Femto LDV do not have this feature.
Despite the advantages of lasers with spherical contact surfaces, which include lower IOP, less subconjunctival hemorrhage, potentially more patient comfort and no loss of patient fixation, they require a reasonably compliant patient. Because of the low vacuum, a noncompliant patient “can actually break suction during the treatment if he does not cooperate. So you do need patient cooperation,” Dr. Yoo said
The ability to create channels for intracorneal rings or corneal implants is a feature of the IntraLase, WaveLight FS200 and Femto LDV. These three laser systems, plus the VisuMax, can also perform penetrating and lamellar keratoplasty.
Femtosecond laser refractive surgery entails carving an intrastromal lenticule of a desired shape to induce refractive change, whereas the VisuMax technique allows for femtosecond lenticular extraction by creating a LASIK flap that is then lifted.
“You’ll see that there is peeling off of the lenticule of the desired thickness and shape in order to correct myopia, for example,” Dr. Yoo said.
The ReLEx smile (small-incision lenticule extraction) technique with the VisuMax is the most recent advance in femtosecond laser technology, according to Dr. Yoo.
“Rather than creating an entire LASIK flap, there is just a very small opening that is made,” she said. “The lenticule is then carefully dissected and pulled out of a pocket.”
Dr. Yoo said the ReLEx smile technique is exciting because it requires only one laser, and the small incision may be less likely to induce dry eye.
“You can also potentially maintain the biomechanical stability of the cornea better than you could with LASIK surgery,” she said.
Complications of femtosecond laser LASIK, although lower than with a microkeratome, include transient light sensitivity, the presence of an opaque bubble layer, epithelial breakthrough and anterior chamber bubbles.
“As we learn more about femtosecond laser technology and gain more experience, and as we are introduced to newer technologies with lower energies and high repetition rates, I think we are seeing less of these complications in our LASIK surgery today,” Dr. Yoo said. – by Bob Kronemyer
For your information:
- Sonia H. Yoo, MD, can be reached at Bascom Palmer Eye Institute, 900 Northwest 17th St., Miami, FL 33136; 305-326-6322; email: syoo@med.miami.edu.
- Disclosure: Dr. Yoo is a paid consultant for Alcon, Allergan, Genentech, Bausch + Lomb, Carl Zeiss Meditec and Transcend.