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Up Front | Apr 2007

Femtosecond Lenticular Extraction

This investigational new procedure is unique to the VisuMax laser, and currently only performed by two clinical investigators in Germany.

In today's refractive market, the demand for femtosecond lasers is continually growing. This relatively new technology has made protecting the cornea's integrity easier and creating flaps more consistent and precise. Because several manufacturers now offer femtosecond lasers, each surgeon must decide what technology is best suited for his/her needs. In my opinion, the VisuMax femtosecond laser (Carl Zeiss Meditec AG, Jena, Germany) (Figure 1) will be the most attractive choice for two reasons. First, it gives the surgeon an extra margin of safety in creating the flap. Second, it offers a very functional workstation concept in combination with the MEL-80 excimer laser (Carl Zeiss Meditec AG). Additionally, I am a clinical investigator of a new technique called femtosecond lenticular extraction. (FLEx). This new innovation in corneal surgery surgery uses a femtosecond laser alone, compared with other procedures that use an excimer plus femtosecond laser.

Marcus Blum, MD, of Erfurt, Germany, and I introduced FLEx at the 2006 American Academy of Ophthalmology Annual Meeting, in Las Vegas. Although the procedure is not yet approved, FLEx has demonstrated the enormous potential of VisuMax, because the quality of cut allows us to extrude the refractive lenticule from the cornea. The following information provides an account of how the procedure works.

FLEx is not LASIK; the healing responses of the two procedures are quite different. For instance, there is no initial overcorrection as seen with the excimer laser. The cornea is not ablated during FLEx like it is when an excimer laser is used. Therefore, energy is not lost at the periphery of the ablation, and prolate refractive zones are similar to wavefront-optimized excimer laser ablation results. Our results with FLEx, which is a single-step procedure (Figure 2) are much better than we ever expected.

HOW IT WORKS
During FLEx, the femtosecond laser creates a refractive and a nonrefractive cut in a single step. After the flap is lifted, a piece of stromal corneal tissue (ie, refractive lenticule) is removed. Next, the flap is repositioned in the usual fashion. This new procedure has an enormous potential. Currently, we have 3-month results, however, Carl Zeiss Meditec AG will soon release the 6-month follow-up data. At 3 months, all patients treated with FLEx were 20/40 or better uncorrected. If we can customize and further improve upon the FLEx procedure, surgeons could conduct an entire lamellar refractive procedure with the femtosecond laser alone.

MY EXPERIENCE
In addition to performing the FLEx procedures, I also have experience in cutting flaps with the VisuMax. As the laser's chief investigator, I had been using the laser's prototype for more than 1 year.

The final version of the VisuMax femtosecond laser was released for clinical validation in February. We have treated 32 myopic eyes using the VisuMax/MEL-80 platform (Carl Zeiss Meditec AG). The results have been spectacular; a few patients have experienced 20/10 uncorrected vision 1 day following surgery. I have cut very thin flaps as well as thick flaps (range, 100 µm to 150 µm). In the more than 50 procedures I have performed so far, I have never created a buttonhole, tear, or any other complication that one experiences with normal microkeratomes.

I have found added benefit to using the VisuMax compared with other femtosecond lasers for flap creation, because the laser's platform has been perfected to improve patient workflow. This platform creates a workflow that is at least partially comparable to microkeratome LASIK, which is a very fast procedure.

Over the past year, Carl Zeiss Meditec AG has tremendously improved the platform of the VisuMax, as the prototype already has achieved great functionality and cut quality. The platform that VisuMax now offers is more user-friendly; it includes an eccentric rotating table. This feature is different from other femtosecond lasers. The built-in rotating patient table alleviates the need for patients to get up and move to the excimer laser. After the surgeon concludes cutting the flap, the patient is rotated 180º to the excimer laser. The laser also has a touch screen that may be covered with a sterile foil, allowing the screen to be used like any phaco or vitrectomy machines.

Another benefit to using the VisuMax is the fast disappearance of gas bubbles. With old femtosecond lasers, the excimer laser's eye tracker would not find the pupil as quickly as it does after a VisuMax flap cut.

MAJOR DIFFERENCES SEEN
If we compare VisuMax to some other femtosecond lasers currently on the market, there are several differences. (1) Femtosecond lasers with applanation systems use a suction ring that applies suction to the sclera via the conjunctiva. It blacks out the eye, similar to the microkeratome. With the VisuMax femtosecond laser, the suction, which is applied to the edge of the cornea and limbus, is very low. Additionally, VisuMax uses a curved surface contact glass with a blinking light inside that allows the patient to see light throughout the entire procedure. This is, in my opinion, a big advantage, because when the eye is blacked out, the retinal central artery is shut down. (2) A high suction level, as with other femtosecond machines, may cause very small subconjunctival bleedings. This will cause the eyes to look red in the days following surgery. With the VisuMax, the eyes look white—as if you have not done anything to them. (3) Similar to a microkeratome, some other femtosecond lasers on the market compress the cornea in a sandwich-like manner to create a parallel, horizontal, or vertical cut. You cannot, as far as I understand, perform refractive treatments with these devices. With the VisuMax femtosecond laser, on the other hand, the cornea is not compressed.

As I mentioned earlier, each surgeon must choose the adequate femtosecond laser for their needs, if they choose to employ a femtosecond laser in the first place. I believe the VisuMax femtosecond laser to be an appealing femtosecond laser for my purposes, because the feasibility of refractive corrections demonstrates the superior cut quality of the VisuMax system.

We expect a futher intense phase of clincial research before this procedure might become commerically available, however, the FLEx has the potential to revolutionize the entire course of corneal refractive surgery. This is the fascinating procedure of the future.

Walter Sekundo, MD, is Professor of Ophthalmology and Deputy Chairman, at the University Eye Hospital of Mainz, Germany. Professor Sekundo states that he is a paid consultant for Carl Zeiss Meditec AG. He may be reached at sekundo@augen.klinik.uni-mainz.de.

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