Current Aspects: Corneal Surgery With the Femtec Laser
Femtosecond solid-state lasers are gaining more popularity in many fields of medicine. They are already used in neurosurgery and dentistry. Now, femtosecond lasers also offer advantages for ophthalmologists, due to their precise performance and the fact that the cornea is transparent for the laser beam (in contrast to excimer laser beams).1 This allows for laser treatment of deep corneal layers such as the endothelium or posterior stroma.
Currently, four US Food and Drug Administration- approved laser systems are available on the market: Femtec (20/10 Perfect Vision, Heidelberg, Germany), Femto LDV (Ziemer Ophthalmic Systems, Port, Switzerland), IntraLase FS laser (IntraLase Corp., Irvine, California), and VisuMax (Carl Zeiss Meditec AG, Jena, Germany). All of these systems are based on the same working principle. In comparison to the IntraLase and Femto LDV (formerly known as the Da Vinci) lasers, the Femtec (Figure 1) and VisuMax laser systems use a patient interface that is similarly curved to match the human cornea (Figure 2). Due to this similar curvature, only low suction-energy is necessary when the eye is connected to the laser, and therefore vision blackouts during surgery are avoided and ocular tissues protected.
FLAP PREPARATION
So far, femtosecond lasers are mainly used for LASIK flap preparation in corneal refractive surgery. Compared with mechanical microkeratomes, femtosecond laser technology features a more precise cut. For example, with the Femtec laser system, the LASIK flap thickness standard deviations are between 9 µm and 11 µm, depending on the intended flap thickness.2 Mechanical microkeratomes used to have standard deviations between 20 µm and 35 µm; only the latest available systems like the Amadeus II (Advanced Medical Optics, Inc., Santa Ana, California) or Carriazo-Pendular (Schwind eye-tech-solutions, Kleinostheim, Germany), with standard deviations between 12 µm and 15 µm, come close to the accuracy of the femtosecond laser.
Generally, one big advantage over mechanical microkeratomes is the possibility to individualize each LASIK procedure and choose between any hinge position, flap diameter, and thickness. This is especially beneficial in thin cornea cases, as femtosecond lasers assist by cutting thinner flaps. Thus, it helps avoid postoperative complications (eg, corneal ectasia) when high amounts of corneal tissue need to be ablated.
FIRST PK PERFORMED
In addition to LASIK flap cuts, lamellar and penetrating keratoplasties as well as corneal tunnel preparation for intracorneal ring segments and incisions to correct astigmatism may be performed using this new technology.3 In 2005, Mark Tomalla, MD, of Duisburg, Germany, performed the first PK using the Femtec femtosecond laser. Now, we have 18-month follow-up from the first 12 patients who underwent penetrating keratoplasty at the Department of Ophthalmology, University of Heidelberg, Germany, using the Femtec laser system. Patients suffered from Fuchs' endothelial dystrophy, keratoconus with corneal scars, familiar granular dystrophy, herpetic keratitis with corneal neovascularization, or endothelial decompensation. Both donor (using an artificial anterior chamber) as well as recipient corneas were treated with the Femtec laser. Each surgery took approximately 2 minutes per cornea, and all cuts were uneventful. Even hazy corneas with neovascularization were treated without any complications. Typically, the laser cut started at approximately 1,000-µm depths in the anterior chamber and moved in a circular fashion through the endothelium, stroma, and epithelium. Remaining tissue fibers helped to maintain a deep anterior chamber and a stable eye. Excised corneas were histopathologically examined and revealed straight precise cuts without any irregularities. After 1.5 years, no patient experienced any complication.4
INDIVIDUALLY CHOSEN AND ADAPTED
The use of a femtosecond laser such as the Femtec in PK has the big advantage that the diameter of the transplant—as well as the cut angulation—may be individually chosen and adapted to the patients surgical needs. Surgeons are able to customize their keratoplasty surgery to the patients' corneal disease. The current Femtec laser model now has a speed that is four times faster than the initial laser system, which expedites the surgical procedures. New procedures that may be done using the Femtec femtosecond laser now also include posterior lamella keratoplasty. Furthermore, this device allows cutting the lamellar without opening the eye.
Corneal tunnel preparation for intracorneal ring segments in keratoconic patients may also be performed precisely and customized to the surgical needs with femtosecond lasers. The surgeon needs less than 1 minute to prepare such a tunnel, followed by ring segment insertion. The procedure is completed by closing the tunnel with one suture, and the visual recovery is very quick.5,6
Certainly, further applications of this new technology will arise. Experimental studies are already underway to investigate exciting new techniques with the femtosecond laser. One example is intracorneal refractive corrections without the need for corneal incisions. It will be interesting to follow these studies and further developments in the field of femtosecond laser technology in the future.
Mike P. Holzer, MD, is a faculty member, Cataract, Cornea, and Refractive Surgery, at the International Vision Correction Research Centre, Department of Ophthalmology, University of Heidelberg, in Germany. Dr. Holzer states that he has no financial interest in the products or companies mentioned. He may be reached at Mike.Holzer@med.uni-heidelberg.de.
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