Femtosecond laser elevates flap creation to higher level

April 15, 2005

Each of the lasers can cut to depths up to 400 ?m and can create flaps with a minimum thickness of 90 ?m.

Femtosecond technology represents the state of the art for creating surgical incisions in the cornea, according to Perry S. Binder, MD.

The first clinical use of the femtosecond laser in the cornea occurred in 1998. In 2000, the first U.S. cases of femtosecond LASIK flap creation were performed, and the commercial launch of the Intralase FS (IntraLase, Irvine, CA) took place in 2001.

Comparison of devices Dr. Binder told attendees the two devices share some similarities but are also different in a number of ways. The IntraLase and FEMTEC devices both feature a wavelength of 1,060 nm, but the current version of the IntraLase operates at a faster rate than the FEMTEC, 15 versus 12.5 kHz, respectively. In addition, the IntraLase has a smaller spot size and the spacing between the spots can be varied whereas that parameter is fixed with the FEMTEC laser.

Scanning control for the bed is two-dimensional for the IntraLase laser and three-dimensional for the FEMTEC. The latter laser operates with a spiral pattern while the IntraLase can be used with a spiral or raster pattern. Both devices create a planar lamellar dissection.

The IntraLase has a flat applanation surface that necessitates strong corneal contact. In contrast, the FEMTEC device has a curved applanation surface and corneal contact is soft. Consequently, applanation pressure is lower with the FEMTEC, although IOP rises to 30 mm Hg using both devices.

Each of the lasers can cut to depths up to 400 µm and can create flaps with a minimum thickness of about 90 µm. The maximum achievable flap diameter is larger for the IntraLase versus the FEMTEC (9.5 versus 8 mm). Total time for the bed cut is 45 seconds with the IntraLase and 60 seconds with the FEMTEC.

Clinical experience using the IntraLase femtosecond laser microkeratome indicates it can be used safely to create flaps of predictable thickness, Dr. Binder said.

He explained that four different groups of investigators have published their results using the IntraLase laser for LASIK flap creation in the first series of eyes. Across those studies, which included about 350 cases, the standard deviation for mean flap thickness was very low, ranging from 12 to 19 µm.

"Those results are pretty impressive and I would expect they would be difficult to replicate in a similar scenario using any mechanical microkeratome," Dr. Binder said.

He reported that unpublished results from his own consecutive series of eyes show similarly excellent results. For intended flap thicknesses of 100, 110, and 120 µm, the means for achieved flap thickness were 104, 114, and 124 µm, respectively, and the standard deviation for each group ranged from 10 to 12 µm. In contrast to the situation with mechanical microkeratomes, flap thickness results using the femtosecond laser device were independent of corneal pachymetry and curvature.

"Using ultrasound pachymetry and the subtraction technique for calculating flap thickness, there is probably a 10-µm limit for standard deviation. Overall, it seems what you ask for is what you get with respect to flap thickness using the femtosecond laser microkeratome," Dr. Binder said.

Refractive outcomes of procedures performed with the femtosecond laser microkeratome are highly predictable.