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The latest version of a proprietary femtosecond laser (iFS, Abbott Medical Optics) offers a 150-kHz repetition rate and expanded options for flap customization.
"The newest version of this femtosecond laser is providing surgeons with many attributes desired in an instrument used for LASIK flap creation," said Dr. Lindstrom, founder and attending surgeon, Minnesota Eye Consultants, Minneapolis. "It effectively creates easy-to-lift flaps with increased efficiency and minimal inflammation . . . and allows for greater customization, including options providing stronger flap adherence.
"As this technology becomes better and better, . . . surgeons [may] also be able to measure the improvements in terms of enhanced clinical outcomes," he added.
"Patients still feel a little pressure when the suction ring is on, but the procedure is now very quick, so the duration of any discomfort is much shorter," he said.
The faster repetition rate also allows the use of tighter raster patterns and lower energy settings. As alternatives to the classic 8 X 8 µm or 9 X 9 µm pulse separations, Dr. Lindstrom said that some surgeons are using a 5 X 5, 6 X 6, or 7 X 7 µm pattern.
"Tighter [raster patterns] and lower energy reduce inflammation and the risk of diffuse lamellar keratitis as well as result in smoother beds and easier flap lifts," he said.
Options for flap customization also have been expanded. Surgeons now can create elliptical (oval) flaps instead of simply round flaps, and they can modify the side cut angle to create a bevel-in configuration with an inverted angle of up to 150°.
"An oval flap has potential advantages in some procedures, especially when treating astigmatism, and it also helps to move the hinge out of the way of the ablation," Dr. Lindstrom said. "In addition, an oval flap helps preserve vital corneal fibers in the periphery that contribute to corneal biomechanical strength and minimizes nerve resection to reduce the risk of dry eye."
Emerging evidence on the benefits of the inverted side cut has been very interesting, he said.
"Initially, I was unsure if an inverted side cut would have positive or negative consequences, but in theory, it seemed it may have benefits for improving flap adhesion strength and reducing epithelial ingrowth, especially after enhancement," Dr. Lindstrom said. "Subsequently, research conducted by Michael Knorz, MD, in animal eyes and by Arturo Chayet, MD, in humans confirm that the bevel-in side cut is associated with stronger adhesion, and this technique is being adopted by most surgeons with access to the new femtosecond laser."
Flap repositioning also is easier using the bevel-in side cut, he said, and data are being collected to investigate the hypothesis that this configuration reduces the incidence of microstriae, macrostriae, and flap slippage.