What's Hot in Femtosecond Laser Technology

In June, 155 surgeons, industry representatives, and ophthalmic residents convened in Bordeaux, France, to discuss the impact of femtosecond laser technology in ophthalmology. This 1-day conference reviewed the fundamental aspects of femtosecond laser-tissue reaction and highlighted the technology's present and future applications in corneal, cataract, refractive, glaucoma, and retinal surgery.

Five topics were the focus of the Third International Conference on Femtosecond Laser in Ophthalmology: (1) fundamental advancements in femtosecond technology for ophthalmology, (2) LASIK and intrastromal corneal rings, (3) keratoplasty, (4) presbyopia and cataract surgery, and (5) commercially available femtosecond laser units for ophthalmic surgery. Course directors were Joseph Colin, MD; David Touboul, MD; and Laurent Sarger, PhD. This article provides an overview of selected lectures.

FUNDAMENTAL ADVANCEMENTS
An experiment conducted at the Institut National de la Recherche Scientifique in Varennes, Quebec, Canada, suggests that damage to surrounding corneal tissue during femtosecond laser use may be reduced by generating microcavities with less energy.¹ Jean-Claude Kieffer, PhD, presented research indicating that near–single-cycle pulses (range, 7 femtoseconds at 800 nm to 13 femtoseconds and 1.4 µm) produce a safer ablation profile. These experimental high-energy near–single-cycle pulses are currently produced at the institute's advanced laser light sources facility. This laser system is the first technology to use a high average power cluster of Ti:sapphire (10–50 W at 25 femtoseconds). By decreasing the pulse duration toward the single-cycle limit and increasing the wavelength to 1.6 µm, the researchers believe this laser creates less thermal effect and scattering and produces less damage along the propagation axis (Figure 1).

Previous studies by Kieffer et al showed that the ablation threshold plateaus between 100 femtoseconds and 1 picosecond but increases during larger pulse durations. Additionally, the researchers used a numerical modeling system for short pulse durations and found that the plateau extends to 30 femtoseconds for short pulse durations and decreases rapidly for shorter pulses.

LASIK AND INTRASTROMAL CORNEAL RINGS
Omid Kermani, MD, reported on the application of optical coherence tomography (OCT) to guide sub-Bowman's keratomileusis flap creation with a femtosecond laser at a 10-MHz repetition rate.² During the study, real-time OCT, via video monitoring, was used to ensure placement of the 10-mHz flap just underneath Bowman's layer in five cadaver eyes unfit for transplantation. Eyes were examined with light or electron microscopy.

According to Dr. Kermani, the corneal epithelium was distinct in all eyes, but Bowman's membrane was not always identifiable due to the resolution of the OCT. However, as confirmed with microscopy, real-time OCT did ensure correct positioning of the cut at the proper depth under Bowman's membrane.

KERATOPLASTY
Femtosecond-assisted lamellar keratoplasty was the focus of the lecture Rudy M. M. A. Nuijts, MD, PhD, delivered.³ He said it is beneficial to use the femtosecond laser for keratoplasty because the surgeon can customize the thickness of the graft. Additionally, with the uses of OCT, the surgeon can estimate the exact depth of corneal scarring and accurately program the graft thickness.

Dr. Nujits randomly assigned 80 eyes of 80 patients to receive femtosecond laser-assisted Descemet's stripping endothelial keratoplasty (FS-DSEK; Figures 2 and 3) or penetrating keratoplasty (PKP). All eyes were previously diagnosed with Fuchs' endothelial dystrophy, pseudophakic bullous keratopathy, or posterior polymorphous dystrophy. Dr. Nuijts compared the visual outcomes, endothelial cell density, and complication profiles of both procedures. He determined that refractive and topographic astigmatism remained stable in the FS-DSEK group and significantly increased in the PKP group (P<.05). Patients in the FS-DSEK group were more likely to have a hyperopic shift, whereas patients in the PKP group progressed toward a myopic shift (P<.001).

Dr. Nuijts and colleagues found that mean endothelial cell loss was higher in the FS-DSEK than the PKP group (65 ±12% vs 23 ±15%, respectively). He suggested that, if the insertion technique during FS-DSEK is modified, the amount of endothelial cell loss may be reduced. This is essential for long-term graft survival, Dr. Nuijts said.

PRESBYOPIA AND CATARACT SURGERY
Use of the femtosecond laser in cataract surgery will advance the manual procedure to a laser-precise, computer-controlled technique, Tibor Juhasz, PhD, said.⁴ Dr. Juhasz presented information on a study of 60 manual and 60 femtosecond-assisted cataract surgeries conducted by Zoltan Nagy, MD, PhD (Figure 4). During the study, Dr. Nagy noted perfect centration and easy and complete removal of the capsule in eyes with laser capsulotomy.

If the patient's lens was soft or medium grade, the laser was used to liquefy the nucleus, and irrigation/aspiration was used for lens removal. If the patient's lens was hard, laser incisions were used to chop the lens, resulting in the reduction of phacoemulsification time. There were no adverse events and no radial tears. Additionally, 100% of all laser-created capsulotomies measured within ±0.25 mm of the intended diameter.

Dr. Juhasz said that the study demonstrated the following advantages of femtosecond-assisted cataract surgery over a manual technique: efficient lens fragmentation or liquefaction, precise creation of the capsulotomy, and reproducible corneal incisions. The use of femtosecond lasers in cataract surgery will advance the level of refractive cataract surgery, he concluded.

COMMERCIALLY AVAILABLE UNITS
Femtosecond laser systems discussed at the conference included the IntraLase iFS (Abbott Medical Optics Inc., Santa Ana, California), Technolas (Technolas Perfect Vision GmbH, Munich, Germany), Femto LDV (Ziemer Group, Port, Switzerland), and the VisuMax (Carl Zeiss Meditec, Jena, Germany). According to Perry S. Binder, MD,⁵ the iFS laser, now operating at 150 kHz, can create a 9-mm flap in less than 12 seconds, and it reduces spot/line separation to increase the smoothness of the stromal bed.

The Technolas' high-speed engine reduces treatment times and also allows a smoother stromal bed, said Frieder Loesel, PhD.⁶ The laser's IntraCOR treatment is a new approach to presbyopia correction with indications expanding to the correction of myopia, hyperopia, and astigmatism, he said.

The proprietary technology of the Femto LDV generates stability of the femtosecond pulses, said Anton C. Wirthlin, PhD.⁷ He described the laser's new lamellar corneal surgery module, which has a video camera built into the handpiece and a deeper focus depth (500 µm). Visual markers are displayed on the monitor to facilitate centering, Mr. Wirthlin said, and a fixation light supports patient fixation.

The curved interface of the VisuMax allows the patient to maintain vision during surgery and scanning, said Dirk Muehlhoff, MSc.⁸ The low pulse energy of the 500-kHz VisuMax decreases bubble formation and tissue deformation, he said.

1. Kieffer JC. Femtosecond lasers in ophthalmology: Near single cycle pulses and beam shaping to benchmark numerical modeling. Paper presented at the: Third International Conference on Femtosecond Laser in Ophthalmology; June 12, 2009; Bordeaux, France.
2. Kermani O. Real-time optical coherence tomography-guided femtosecond laser sub-Bowman's keratomileusis: Experimental results. Paper presented at the: Third International Conference on Femtosecond Laser in Ophthalmology; June 12, 2009; Bordeaux, France.
3. Nuijts RMMA. Femtosecond laser-assisted lamellar keratoplasty. Paper presented at the: Third International Conference on Femtosecond Laser in Ophthalmology; June 12, 2009; Bordeaux, France.
4. Juhasz T. Femtosecond lasers for cataract surgery. Paper presented at the: Third International Conference on Femtosecond Laser in Ophthalmology; June 12, 2009; Bordeaux, France.
5. Binder PS. The IntraLase/FS5 femtosecond laser system. Paper presented at the: Third International Conference on Femtosecond Laser in Ophthalmology; June 12, 2009; Bordeaux, France.
6. Loesel F. The Technolas Perfect Vision/Femtec femtosecond laser system. Paper presented at the: Third International Conference on Femtosecond Laser in Ophthalmology; June 12, 2009; Bordeaux, France.
7. Wirthlin AC. The Ziemer Femto LDV. Paper presented at the: Third International Conference on Femtosecond Laser in Ophthalmology; June 12, 2009; Bordeaux, France.
8. Muehlhoff D. The Carl Zeiss Meditec/VisuMax femtosecond laser system. Paper presented at the: Third International Conference on Femtosecond Laser in Ophthalmology; June 12, 2009; Bordeaux, France.