New femtosecond laser provides cutting accuracy and ‘gentle touch’

In addition to LASIK applications, the VisuMax system performs the new femtosecond lenticle extraction procedure.

ByMichela Cimberle

Preliminary results of refractive surgery with the new Carl Zeiss Meditec VisuMax femtosecond system show that this technology is accurate and has a “gentle touch” that causes minimal trauma to the eye.

According to Marcus Blum, MD, and Walter Sekundo, MD, investigators for Carl Zeiss Meditec, the VisuMax represents “an innovative concept for refractive laser surgery,” and its advantages “are not limited to those normally associated with other femtosecond laser systems.”

In the field of refractive surgery, in addition to the femtosecond laser flap cut for LASIK and excimer laser ablation, a new investigational method that relies entirely on the femtosecond laser technology has been developed.

Clinical studies of the laser system are currently being carried out in the German cities of Mainz and Erfurt by Drs. Sekundo and Blum. Preliminary results were first presented at the American Academy of Ophthalmology meeting in Las Vegas.

The VisuMax femtosecond laser was approved by the U.S. Food and Drug Administration for creating corneal flaps in LASIK procedures in January.

The ‘gentle corneal interface’ concept

Due to the special design of the contact glass, the VisuMax creates a spherical contact interface with the cornea. Suction is applied only a few seconds longer than the actual laser therapy time, with low pressure that does not impair the perfusion of the central retinal artery.

How it works

The VisuMax creates and compresses laser light in short laser impulses. If the laser beam is focused intensely on the tissue, the tissue is transformed into a gaseous plasma in the focus space. A microscopically small gas bubble is formed, which creates a break in the tissue. If the laser beam is led through the tissue, a separating surface then appears, which one can imagine as a dense bubble rug. Because of the extremely short duration of the laser impulses used (1 femtosecond equals 10^-15 seconds), the procedure is called a femtosecond laser incision.

“These characteristics, which we have synthesized in the ‘gentle corneal interface’ concept, result in precise treatment positioning, minimal applanation and no vision loss during suction. The patient is able to see the fixation light during the docking procedure, and due to this fact we have had less decentration,” Dr. Blum said.

In the LASIK study, a combined treatment of flap incision with the VisuMax with an excimer laser treatment with the Carl Zeiss Meditec MEL 80 was performed.

“The VisuMax produced high-quality flap incisions, moving at a fast and regular speed along a line that was perfectly parallel to the surface of the cornea,” Dr. Blum said. “Immediately after treatment, the suction was released, and the cut surface was still visible as a fine bubble layer. By the time we were ready to lift the flap, the bubbles disappeared, and the stromal bed as well as the sidecut had a smooth surface with a fine structure.”

The Visante OCT confirmed the high flap quality, which was precise, homogeneously parallel to the corneal surface and accurate in depth and thickness, he said.

Flap lifting was easy in all cases, and the patients could immediately undergo the excimer laser treatment, Dr. Blum reported.

Carl Zeiss Meditec has developed a unique pivoting patient bed that allows the surgeon to carry out the entire refractive procedure without having the patient move.

“Thanks to this combination of two lasers in one bed, there is no waiting time between femtosecond flap cut and excimer laser ablation, with increased comfort for both the patient and the surgeon,” Dr. Blum said.

LASIK results

Safety, efficacy and predictability of the treatment show the same good results obtained in other studies of the MEL 80 laser with standard microkeratome LASIK.

In the two clinics, 31 eyes were treated. So far, 28 eyes have completed the 3-month follow-up. The patients have an average age of 34 years and a mean sphere of –4.11 D.

Mean postoperative refraction at 3 months was –0.07 D. Corneal topography showed large, regular optical zones. In almost 88% of the patients, uncorrected visual acuity was 20/20 or better; more than one-third of the patients gained one line, and more than 54% were unchanged.

“Predictability was high, with 93% of the patients being within 0.5 D of intended correction,” Dr. Blum said.

No intraoperative adverse events were reported, and postoperative complications were limited to five cases of minor striae, which were related to the high myopia of the patients rather than the device, he said. The cases disappeared spontaneously over time.

Patient satisfaction was tested with a questionnaire at 1 month. All patients said that their quality of vision improved, and all said they would undergo the treatment again.

The new FLEx method

A second study evaluated the outcomes of a new method of performing refractive surgery that relies entirely on femtosecond technology.

With this new procedure, called femtosecond lenticle extraction (FLEx), the refractive correction is achieved by cutting an intrastromal lenticule with the laser, which is then removed manually.

This process demands a precise three-dimensional incision and stable positioning of the device over the eye. To start, the femtosecond laser cuts the back side of the intrastromal lenticle and then the front side. Then, a superficial flap is performed. The flap is lifted to remove the intrastromal lenticle with forceps and is then repositioned like a LASIK flap.

“This is true all-femto LASIK,” Dr. Sekundo said. “The VisuMax provides a new level of cutting accuracy for corneal incisions, as evidenced by the results of this new procedure.”

Using the FLEx method, 10 patients were operated. Mean age was 39 years, mean sphere was –4.60 D and mean cylinder was –0.25 D. Preop UCVA was 20/200, and preop BCVA was 20/20.

“Operating parameters were flap diameter of 7.5 mm to 8.5 mm, flap thickness of 130 µm to 150 µm and optical zone diameter of 6 mm to 6.8 mm,” according to the study protocol, Dr. Sekundo said.

“One month after surgery, we had good and stable results with minimal regression. In all the eyes, topography showed a homogeneous, slightly prolate optical zone, and wavefront analysis demonstrated that this treatment does not induce higher-order aberrations,” he said.

No intraoperative adverse events were reported, and there were no cases of transient light sensitivity syndrome, diffuse lamellar keratitis or haze. Some microstriae were observed in two cases.

“Early outcomes show that FLEx is safe and effective for the treatment of myopia,” Dr. Sekundo said. “Topography and wavefront measurements indicate the future potential of this new method.”

“More patients and a longer follow-up are necessary to confirm the predictability and stability of the procedure,” Dr. Sekundo said.

For more information:

Marcus Blum, MD, can be reached at Helios Clinic, Nordhäuser Str. 74, 99089 Erfurt, Germany; e-mail: marcus.blum@helios-kliniken.de.
Walter Sekundo, MD, can be reached at Universitäts-Augenklinik Mainz, Langenbeck Str. 1, 55131 Mainz, Germany; e-mail: sekundo@augen.klinik.uni-mainz.de. Drs. Blum and Sekundo are investigators for Carl Zeiss Meditec who are doing the clinical trials of the VisuMax femtosecond system.

Carl Zeiss Meditec, maker of the VisuMax femtosecond system, can be reached at Göschwitzer Str. 51-52, 07745 Jena, Germany; Web site: www.meditec.zeiss.com.

Michela Cimberle is an OSN Correspondent based in Treviso, Italy, who covers all aspects of ophthalmology. She focuses geographically on Europe.