Study: femtosecond laser keratome offers clinical advantages

With the femtosecond laser keratome offering clinical advantages over traditional microkeratomes, is the demise of the excimer laser on the horizon?

BOSTON — Creating a corneal flap with a femtosecond laser keratome offers clinical advantages over traditional microkeratomes, which could eventually lead to the demise of the excimer laser when performing laser in situ keratomileusis (LASIK), according to one clinician.

Compared with the Nd:YAG laser, a femtosecond laser has an ultra-short pulse width (femtosecond), which permits “one to use much lower energies,” said Ron M. Kurtz, MD, an assistant professor of ophthalmology at the University in Michigan in Ann Arbor. “These lower energies have much smaller collateral tissue effects; for example, a much smaller cavitation bubble size. This allows one to place pulses very close to each other and, therefore, essentially have contiguous surgical effects.”

When combined with a sophisticated delivery system, “one can essentially deliver any surgical pattern within the corneal stroma,” Dr. Kurtz said. “This can be used to create corneal flaps. There also are other applications to create pockets for implants, potential stand-alone refractive applications, and therapeutic keratoplasty — both full thickness and lamellar.”

Dr. Kurtz shared his enthusiasm for the new technology at the annual American Society of Cataract and Refractive Surgery meeting here. He also is a corporate vice president at IntraLase Corporation (Irvine, Calif.), which has developed a femtosecond laser for ophthalmic applications.

Corneal flap

For the corneal flap pattern, essentially a plane is created at a predetermined depth, after which a partial circle is advanced toward the epithelium to create a hinged side cut. “Some ex vivo comparison studies of the femtosecond laser keratome and mechanical microkeratomes show improved precision, both in terms of flap thickness and flap diameter, with the femtosecond laser,” Dr. Kurtz said.

Most clinical experience with the IntraLase femtosecond laser keratome has been confined to Hungary (46 eyes). An additional four eyes were recently treated in the United States by Lee T. Nordan, MD, an associate clinical professor of ophthalmology at Jules Stein Eye Institute, University of California, Los Angeles. “Refractive correction using standard excimer LASIK nomograms was performed in most instances, both in Europe and in the United States,” Dr. Kurtz said.

For the 50 eyes to date, “there was excellent flap parameter reproducibility,” Dr. Kurtz said. “The intended flap thickness was easily attained within 5 to 10 µm.” Furthermore, several parameters that affected tissue separation (mainly the laser spot size, pulse energy and spot-to-spot separation) were optimized, as well.

Postoperative observations have shown no loss of corneal clarity and excellent flap stability immediately after flap repositioning. “This is primarily due to the architecture of the side cut, which allows essentially no slippage to occur,” Dr. Kurtz said.

First U.S. case

At the meeting, Dr. Nordan presented his first case. Unlike the excimer laser, “this is a focal laser, so we need to dock the eye at a specific distance from the laser within an accuracy of a few microns,” Dr. Nordan said. For the docking system, a suction ring is placed on the eye. “We use the Visx [Santa Clara, Calif.] laser microscope with its fixation light to center things. We then swing the patient’s bed from beneath the Visx laser to the IntraLase laser,” he said.

Dr. Nordan’s IntraLase laser is docked to the suction ring, thereby causing the glass applanation plate to flatten the cornea. The laser then makes a planar cut, thus creating the bed of the keratectomy. “The laser will turn vertical. The precision of this laser is simply astounding,” Dr. Nordan said. Centration is the critical issue, though. “The hinge may be placed wherever you wish,” he said, although in the case presented, a superior hinge was used. “The size and depth of the flap may be varied independently, as well,” Dr. Nordan said.

Large bubbles that appear between the corneal and the applanation plate indicate that the procedure is complete. However, “in this particular case, tissue separation was not perfect, with slight corneal adhesions present, but the corneal bed is of excellent quality,” Dr. Nordan said. The patient achieved 20/25 visual acuity at day 1.

Tremendous capability

“The femtosecond laser has arrived and it has tremendous capability,” Dr. Nordan said. “Hopefully, over the next several months, we’ll be making significant improvements to it.” Overall, “I think the femtosecond laser presents exciting potential for both corneal flaps and intrastromal procedures. My expectation is that the femtosecond laser will be widely used in the future.”

Study eyes in Hungary were subjected to endothelial cell counts, “where we have seen no change in over 1 year,” Dr. Kurtz said. Suction applied to the eye also is less with the femtosecond laser compared with mechanical keratomes. “In ex vivo testing, the intraocular pressure is approximately 30 to 35 mm Hg,” he said. Additionally, the walls of the flap are adjustable. “You can start vertical or cut 45° or 50° angles,” Dr. Nordan said. “One of the nice things about this laser is that it is totally adjustable. All of the parameters can be changed.”

Added Dr. Kurtz, “This technology allows a surgeon to create just about any surgical three-dimensional shape in the cornea. Therefore, one can create an endless variety of corneal procedures — both refractive and therapeutic. There also is also no theoretical reason to believe that the laser itself will present any side effects or complications in the cornea, if used appropriately.” The femtosecond laser “has the potential to replace a number of technologies, such as mechanical microkeratomes and other mechanical devices used in the cornea, and even potentially the excimer laser.”

Finally, the new laser is “very cost effective for the applications it performs,” Dr. Kurtz said.

For Your Information:

Ron M. Kurtz, MD, can be reached at the University of Michigan, 1000 Wall St., Ann Arbor, MI 48105; (734) 763-7711; fax: (734) 332-3736; e-mail: rmkurtz@umich.educ. Dr. Kurtz is a corporate vice president at IntraLase Corporation. He has a direct financial interest in the Pulsion FS.

Lee T. Nordan, MD, can be reached at 9834 Genesee Ave., Ste. 209, La Jolla, CA 92037; (858) 457-2220; fax: (858) 587-0528. Dr. Nordan has no direct financial interest in any of the products mentioned in this article. However, he is a shareholder at IntraLase Corporation and a paid consultant for Allergan.

IntraLase Corporation can be reached at 30 Hughes, Ste. 208, Irvine, CA 92618; (949) 461-3321; fax: (949) 462-7191; e-mail: info@intralase.com.