Femtosecond lasers continue to gain ground as improvements are made to microkeratomes

For many years, microkeratomes were strongly tied to LASIK. Various microkeratomes with increasingly better characteristics were developed to make the procedure safer and more reproducible.

However, the femtosecond laser, introduced for ophthalmic use at the beginning of the decade, presented an appealing alternative to the microkeratome: the creation of cleavage planes within the stroma by photodisruption. This technology has evolved rapidly, and various manufacturers are now offering machines with different and increasingly better characteristics that have overcome the problems of the first-generation femtosecond lasers.

This laser technology divided the opinions of refractive surgeons. Some surgeons welcomed the novel modality as a revolution, while others did not believe the advantages of femtosecond cuts over microkeratome cuts were great enough to justify the extra costs involved.

Microkeratomes are still used by the majority of LASIK surgeons, and manufacturers continue to introduce new devices and improve upon existing models.

But as time passes, femtosecond lasers seem to be increasing in popularity, even among the skeptics.

Select the best option for the patient

Lucio Buratto, MD, who runs a large private practice in Milan, Italy, was one of the pioneers of LASIK in Europe. He introduced innovations in the technique and instrumentation, contributed to the development of the Hansatome microkeratome (Bausch & Lomb) and was the first European user of the IntraLase femtosecond laser (Advanced Medical Optics).

Lucio Buratto, MD, was one of the pioneers of LASIK in Europe and he is using both kinds of devices depending on the case. Image: Buratto L

“If you asked me whether I prefer microkeratome LASIK or femtosecond-laser LASIK, I would honestly answer, for most of my patients, I have no preference. It’s a matter of selecting the best option for individual patients,” Dr. Buratto said.

In his practice, he uses both kinds of devices, depending on the case he is operating on, and maintains that both are excellent instruments in expert hands, with specific advantages and drawbacks for each. His favorite microkeratome is currently the Zyoptix XP (Bausch & Lomb), “an important evolutionary step-up for accuracy, usability and friendliness to the patient.”

“This microkeratome produces large, thin, highly predictable 120 µm to 140 µm flaps of exceptional quality, always well centered. The suction ring has been greatly improved, and there is practically no risk of losing suction,” Dr. Buratto said.

However, he said that this instrument is not suitable for small, deep-set eyes. In these cases, he uses the traditional Hansatome or a femtosecond laser.

“Generally speaking, for the average, uncomplicated cases, I still prefer microkeratomes. They are very good, perfectly safe and reliable instruments. The femtosecond laser is heavier on the eye and requires a slightly longer suction time, as well as some waiting time for bubble dissipation, which may cause some discomfort and anxiety in the patient,” he said.

IntraLase is Dr. Buratto’s first choice in eyes in which a micron-perfect centration is needed, in eyes with abnormally large pupils, in nanophthalmic eyes and in eyes in which preoperative aberrations need to be treated. He emphasized that the latest-generation femtosecond lasers are overcoming previous problems.

“They are faster, easier to use, extremely precise, and produce perfect cuts and even smoother surfaces. The creation of cavitation bubbles has been minimized, and the low-energy impact promotes a fast, uneventful and highly predictable recovery of vision,” he said.

Conversion to femtosecond LASIK

Michael C. Knorz, MD, medical director of the FreeVis LASIK Center and a professor at Medical Faculty Mannheim of the University of Heidelberg, Germany, has switched completely to the use of femtosecond laser in LASIK surgery.

“The Amadeus (Allergan) and then the Amadeus II (Ziemer Group) have been my favorite microkeratomes. Personally, I think that from the point of view of safety, user friendliness and versatility, they are unique,” he said. “However, since I started using the IntraLase in 2004, I gradually switched to femto-LASIK, and now I do it in 100% of my patients. I still use the Amadeus II for epi-LASIK, which I perform in corneas that are less than 500 µm in thickness.”

In comparing his results between microkeratome and IntraLase-assisted LASIK, he found that visual outcomes were slightly better in the IntraLase group.

“Thinner and planar flaps weaken the cornea less. In addition, IntraLase flaps heal better and surgical complications are fewer. In our case series, there were almost no epithelial defects, compared with the 5% to 10% resulting from microkeratomes. No incomplete flaps were found,” he said.

In a study on rabbit eyes, Dr. Knorz compared adhesion strength of LASIK flaps created with the Amadeus II microkeratome vs. the latest-generation IntraLase, the iFS.

“Anecdotally, in our clinical routine, we observed that IntraLase flaps were more difficult to lift during re-treatments than microkeratome flaps. We were, therefore, interested in investigating the flap adhesion strength after flap creation with the IntraLase and a mechanical microkeratome,” he said. “Our results in rabbits show that flap adhesion strength, measured 2.5 months after surgery with a tension meter, is more than twice as high with the IntraLase laser as with the Amadeus microkeratome (492 g vs. 210 g).”

Technology for thin flaps

According to Dr. Knorz, femtosecond technology has raised the possibility of cutting thin LASIK flaps without the typical microkeratome-related complications such as flap folds, irregularities, buttonholes and free caps.

A thinner flap has a lesser impact on corneal biomechanics, lowers the risk of keratectasia and leaves a greater amount of stroma for higher correction capabilities.

“The IntraLase femtosecond laser can produce thin, planar flaps that, compared with the meniscus-shaped flaps of microkeratomes, minimize corneal weakening and induction of spherical aberration,” Dr. Knorz said. The inverted, bevel-in side-cut angle created by the iFS may result in even less biomechanical change in the periphery.

However, even when cutting within a “thin” range, there is no need to go too thin, he noted.

Theoretically, a flap could be as thin as 70 µm to 80 µm. This would include the epithelium at approximately 50 µm to 60 µm and the Bowman’s layer at approximately 10 µm. Practically, taking into account individual epithelial thickness variability, the manufacturing tolerances of the disposable docking cones and other small variables such as a wet or a dry corneal surface, a flap thickness of about 100 µm seems to be clinically better and an acceptable compromise, Dr. Knorz said.

“The advantages of thin flaps are maintained [at 100 µm], but with a higher predictability and complete safety,” he said.

The feasibility and potential benefits of thin-flap femtosecond LASIK with a different machine, the Ziemer LDV (formerly the Da Vinci, Ziemer Group), were evaluated by Jérôme C. Vryghem, MD, who works in the Brussels Eye Doctors private practice in Belgium. Thanks to the InterShield spacer, the Ziemer laser can create flaps of variable thickness from 80 µm to 140 µm and, according to Dr. Vryghem, is “a fantastic tool to create thin flaps safely and reproducibly.”

Starting in January 2008, he set up a study in which 133 eyes underwent Z-LASIK — LASIK with the Ziemer LDV laser — with a 90 µm flap and 33 eyes had an 80 µm flap.

“Undeniably, we had more complications than with the standard 110 µm flaps. From bubble formation with underlying flap adherence to microfolds, striae and haze. They occurred in a minority of cases, but still too many to justify the routine use of this thickness. In addition, relifting the flap in case enhancement is needed can easily lead to flap tears,” Dr. Vryghem said.

After this experience, he went back to using the 110 µm InterShield spacer, obtaining a mean flap thickness of little more than 100 µm, with a tight standard deviation of 9 µm, which is “thin enough but safer,” he said.

He treated about 1,500 patients using this flap thickness with successful outcomes and no clinically relevant complications. Dr. Vryghem recommended the 90 µm thickness only in thin corneas or in highly myopic eyes. The 80 µm flap trial has been discontinued.

He said he uses a microkeratome in less than 1% of his cases in patients who are not ready to pay the extra costs involved with the use of the femtosecond laser.

Thin flaps with a planar architecture can also be achieved with the new Moria One Use-Plus SBK microkeratome, according to Richard A. Norden, MD, of Ridgewood, N.J., U.S.A. Dr. Norden also has a femtosecond laser in his center and said that his first results with the new microkeratome in 100 µm flap LASIK equal those of the femtosecond laser, with some additional, non-negligible advantages.

“The time of procedure is shorter, about 8 minutes on average. Uncorrected visual acuity at 10 minutes postop is impressive, with no photodisruption-induced inflammation and no pain at all experienced by the patients,” he said.

The SBK head and ring are single-use devices, which helps eliminate complications and risks connected with reusable heads. The elimination of sterilization and maintenance and the short suction time and overall procedure time allow for a fast patient turnover.

Dr. Norden said flap thickness is extremely predictable, and contrary to most microkeratomes, the flap is planar, with no meniscus shape.

Special uses of femtosecond lasers

Mark Tomalla, MD, of the Duisburg Niederrhein Clinic in Germany, has been a Femtec femtosecond laser (20/10 Perfect Vision) user since 2004, but he still likes his Hansatome microkeratome for routine cases.

“I do prefer all-laser LASIK, particularly after the introduction of the new 40 Hz machine in my practice, but there is a higher price to pay for the patient. Personally, I think it’s ethically correct to offer the femtosecond laser option to patients with thin corneas or high astigmatism,” he said.

The true revolution brought by femtosecond technology in refractive surgery is, in his opinion, the intrastromal intraCOR treatment, “a new way of addressing potentially all refractive errors, and particularly presbyopia.”

Using special software with the Femtec laser, a series of concentric cuts is created within the intrastromal volume without affecting either the surface of the cornea or other vital structures, such as the endothelium, Bowman’s layer or Descemet’s membrane. A localized reorganization of biomechanical forces is induced within the treatment area, leading to a central, intrastromal steepening with smooth transition zones and consequently increased depth of field.

“A new mechanical equilibrium is generated, and the cornea is reshaped. The refractive power is locally changed, leading to significantly improved near vision and good intermediate vision without affecting distance vision,” Dr. Tomalla said.

This treatment has had good results so far in trials, he said.

Another promising option offered by femtosecond technology is FLEx (femtosecond lenticule extraction) with the VisuMax laser (Carl Zeiss Meditec).

The laser dissects a lenticule of corneal tissue and then creates a flap as a single-step procedure. The refractive lenticule is then manually removed by the surgeon, using special instruments.

“This extraction creates the refractive effect,” Walter Sekundo, MD, of Philipps University of Marburg, Germany, said.

In the first 10 eyes of a multicenter study carried out in Germany, this technique has shown promising results in the correction of myopia and myopic astigmatism. Ninety percent of eyes were within ±1 D of intended correction and 40% were within ±0.5 D. The 6-month results of 106 eyes, as presented at the European Society of Cataract and Refractive Surgeons meeting in Berlin, shows 80% of treated eyes were within ±0.5 D.

Dr. Sekundo said that the VisuMax system is also a good, reliable machine to create a conventional LASIK flap, but that the idea of going beyond simple flap making and eliminating the need for two lasers is appealing.

New microkeratomes have improved features

Flap creation is perhaps the most important stage of LASIK. Many of the most serious LASIK complications occur during cutting the flap or are a consequence of cutting, including the refractive surgery nightmare of post-LASIK ectasia.

Initially, these complications were a threat to the procedure. But today, femtosecond lasers and the new generation of microkeratomes make LASIK a safe procedure, almost eliminating all risks if used by expert surgeons.

“I think that wherever surgeons have a free choice, femtosecond LASIK will become the standard of LASIK surgery,” Jorge L. Alió, MD, PhD, of the Vissum Eye Institute in Alicante, Spain, said. “However, if price is an issue – and indeed it is – we can still rely on microkeratome LASIK as a very safe and effective alternative.”

The newer designs of microkeratomes have advanced safety features that greatly reduced the risk of flap-related complications, he said. These include voice confirmation, battery power backup, automated safety checks, vacuum loss shutoff and software-driven flap centering.

“Overall, the newer-generation devices are much easier to use and have the capability to cut very predictable flaps with a homogeneous profile,” Dr Alió said.

He explained that the meniscus-shaped flaps that are typical of some traditional microkeratomes have an impact on refractive outcomes because of differences in the coherence of the optical surfaces following excimer laser ablation. They also induce a more oblate profile of the anterior corneal surface with an impact on contrast sensitivity and corneal spherical-like aberrations.

However, some microkeratomes, such as the Schwind Carriazo-Pendular, create planar flaps, similar to those of femtosecond lasers.

“Using high-frequency ultrasound scanning with the Artemis 2 (ArcScan), we demonstrated that the LASIK flaps produced by the IntraLase and the Carriazo-Pendular microkeratome had comparable thickness predictability and a very similar planar profile,” Dr Alió said. – by Michela Cimberle

Is the age of microkeratomes coming to an end?

References:

• Alió JL, Piñero DP. Very high-frequency digital ultrasound measurement of the LASIK flap thickness profile using the IntraLase femtosecond laser and M2 and Carriazo-Pendular microkeratomes. J Refract Surg. 2008;24(1):12-23.
• Knorz MC, Vossmerbaeumer U. Comparison of flap adhesion strength using the Amadeus microkeratome and the IntraLase iFS femtosecond laser in rabbits. J Refract Surg. 2008;24(9):875-878.
• Norden RA. Patient and practice benefits of One Use-Plus SBK. Presented at: American Academy of Ophthalmology meeting; November 2008; Atlanta.
• Ruiz LA. Intrastromal refractive correction with no flap. Presented at: World Ophthalmology Congress; June 2008; Hong Kong.
• Sekundo W, Kunert K, Russmann C, et al. First efficacy and safety study of femtosecond lenticule extraction for the correction of myopia: six-month results. J Cataract Refract Surg. 2008;34(9):1513-1520.
• Vryghem JC. 90 and 80 micron flaps in LASIK with the Ziemer LDV femtosecond laser: Early results. European Society of Cataract and Refractive Surgeons; September 2008; Berlin.

• Jorge L. Alió, MD, PhD, can be reached at Vissum, Instituto Oftalmologico de Alicante, Avda. de Denia, s/n, 03016 Alicante, Spain; +34-965-150-025; fax: +34-965-151-501; e-mail: jlalio@vissum.com.
• Lucio Buratto, MD, can be reached at CAMO, Piazza Repubblica 21, 20124 Milano, Italy; +39-02-6361191; fax: +39-02-6598875; e-mail: office@buratto.com.
• Michael C. Knorz, MD, can be reached at FreeVis LASIK Center, Klinikum Mannheim, Theodor Kutzer Ufer 1-3, 68167 Mannheim, Germany; +49-621-3833410; fax: +49-621-3833803; e-mail: knorz@eyes.de.
• Richard A. Norden, MD, can be reached at Norden Laser Eye Associates, 1144 East Ridgewood Ave., Ridgewood, NJ 07450, U.S.A. +1-866-614-9220 ; fax: +1-201-444-472; e-mail: rnorden@nordenlasik.com.
• Walter Sekundo, MD, can be reached at Philipps University, Department of Ophthalmology, Robert-Koch Strasse 4, 35037 Marburg, Germany; +49-6421-5866275; fax: +49-6421-5865678; e-mail: sekundo@med.uni-marburg.de or stosseck@med.uni-marburg.de.
• Mark Tomalla, MD, can be reached at Klinik für Refraktive & Ophthalmo-Chirurgie, Fahrner Strasse 133, 47169 Duisburg, Germany; +49-203-5801711; fax: +49-203-5081713; e-mail: mark.tomalla@ejk.de.
• Jérôme C. Vryghem, MD, can be reached at the Brussels Eye Doctors, 12-16 Boulevard St-Michel, 1150 Brussels, Belgium; +32-2-741-69-99; fax: +32-2-732-71-48; e-mail: j.c.vryghem@vryghem.be or info@vryghem.be.