IntraLase femtosecond laser effective as LASIK keratome

Future applications include laser keratomileusis and lamellar transplantation.

IRVINE, Calif. — The Pulsion femtosecond laser from IntraLase Corp. (Irvine, Calif.) is a non-excimer technology for corneal surgery. Although currently approved only as a laser keratome for corneal resection, the novel laser has numerous potential clinical applications, including creation of intracorneal pockets for implants and lamellar transplantation.

“Femtosecond lasers of 1 µm wavelength normally are not absorbed by the corneal stroma and would ordinarily pass through, not affecting the tissue,” said Ron M. Kurtz, MD, cofounder and medical director at IntraLase. “However, if you focus the laser to a very small spot size — approximately 3 µm — you can generate a plasma and initiate a photodisruptive process that is analogous to the Nd:YAG laser, but far more localized.”

Unlike one pulse, which has a negligible effect, “placing thousands of pulses in a continuous pattern creates essentially any three-dimensional shape intrastromally that has micron accuracy, due to the laser’s computer control,” Dr. Kurtz said.

The IntraLase laser consists of a laser engine, a scanning optical delivery system and a patient interface that applanates the cornea. When the laser is positioned next to an excimer laser, the surgeon creates the corneal flap with the IntraLase laser and then is able to simply rotate the patient under the excimer laser, lift the corneal flap and perform the excimer ablation, according to Dr. Kurtz, an associate clinical professor of ophthalmology at the University of California, Irvine.

Computer control

The surgeon begins by programming the characteristics of the flap. “Because of computer control, he can specify the flap diameter and the flap thickness to 10 µm accuracy,” Dr. Kurtz said. Surgeons can also choose any hinge angle, although they are given the choice of temporal, nasal or superior.

“Because the flap edges are raised, it can be positioned analogous to a manhole cover so that it sits in place quite securely. For that reason, the hinge angle can be fairly small, typically 45°,” Dr. Kurtz said. This exposes more of the stromal bed, allowing greater surface area for the excimer ablation.

As of last October, when Dr. Kurtz spoke at the American Academy of Ophthalmology meeting in Dallas, a total of 220 eyes had undergone laser keratome with the IntraLase femtosecond laser.

“Only four of these eyes had intraoperative events, consisting of early loss of suction and loss of applanation,” Dr. Kurtz said. In each of these cases, “the procedure could be repeated within 30 to 45 minutes, simply by allowing the gas bubbles (produced during photodisruption) to be absorbed by the normal cornea pumping mechanisms.” Further, there have been no incidents of epithelial defects, free flaps, or any of the other commonly reported flap complications.

Most of these 220 eyes had recently been operated on, so only about 34 eyes had reached 3-month follow-up.

“The retention of best spectacle corrected vision has been excellent in this group, as have the refractive results. We had one outlier, although he was a tough refraction and actually had 20/20 uncorrected vision. There has also been some overcorrection at the higher diopters,” Dr. Kurtz said.

Favorable refractive results

For eyes with less than 6 D of myopia and less than 3 D of astigmatism, 64% achieved 20/20 or better at 3 months, 97% were 20/40 or better, and 86% were within 0.5 D of intended correction.

“These results compare favorably with published reports about refractive states,” Dr. Kurtz said. Flaps for all study eyes demonstrated consistent flap depth, diameter, and hinge length with very uniform thickness. Dr. Kurtz shared the results of one patient who at 1 day postop exhibited excellent corneal clarity. “This –7.5 D myope achieved 20/25,” he said.

Dr. Kurtz is enthusiastic about developing applications for the IntraLase femtosecond laser. “Lamellar transplantation, including both anterior and posterior lamellar corneal transplant, is just one area,” he said. A histologic slide showed the cap of the recipient cornea after removal with the laser. “This is a very uniform, 250-µm cap thickness,” Dr. Kurtz said. There was also perfect symmetry over the entire 7.2 mm of the cap.

In European studies, the IntraLase femtosecond laser has been used to create tunnels and entry cuts for intracorneal ring segments, using both the standard vertical incision and an incision outside of the tunnel. The latter “potentially may have some clinical advantages,” Dr. Kurtz said.

“Refractive results have been very analogous to standard Intacs (KeraVision Inc., Calif.), in which four eyes had the Intacs removed, mainly due to undercorrections.” Dr. Kurtz and colleagues are also investigating some stand-alone refractive procedures, such as laser keratomileusis. “We’re using the laser to outline a corneal lenticule and then removing the lenticule through a flap,” he said.

For Your Information:

• Ron M. Kurtz, MD, can be reached at IntraLase Corp., 3 Morgan, Irvine, CA 92618; (949) 609-2959; fax (949) 509-9398; e-mail: rkurtz@intralase.com. Dr. Kurtz is cofounder of the company.