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Early FDA data with a femtosecond laser platform (VisuMax, Carl Zeiss Meditec) show positive results for corneal refractive surgery to treat uncomplicated myopia.
Early FDA data for a femtosecond laser platform (VisuMax, Carl Zeiss Meditec) show positive results for corneal refractive surgery to treat uncomplicated myopia.
San Francisco-The quest for the ideal refractive vision correction procedure is likely to include such attributes as accuracy, effectiveness, stability, safety, and the ability to provide quality outcomes.
The ideal procedure would be reversible or adjustable, involve minimal wound healing, provide immediate and final refractive outcomes, and meet patient expectations. And it must be better than glasses or contact lenses.
“No procedure is perfect on all those counts,” said John F. Doane, MD, in practice at Discover Vision Centers, Kansas City, MO, and assistant clinical professor, Kansas University Medical Center, Kansas City, KS.
“We are always looking for the next best things,” said Dr. Doane at the annual meeting of the American Society of Cataract and Refractive Surgery. “The next best thing in laser vision correction may be all-femtosecond laser procedures.”
Dr. Doane presented early results from the first FDA trials of a certain femtosecond laser platform (VisuMax, Carl Zeiss Meditec) to treat uncomplicated myopia. Though the femtosecond laser is in use outside the United States, this trial was conducted under an investigational device exemption. The five study sites included Denver (Jon Dishler, MD); Kansas City (John Doane, MD); Madison, WI (John Vukich, MD); Miami (William Culbertson, MD, Sonia Yoo, MD), and Sioux Falls, IA (Vance Thompson, MD).
Unlike traditional LASIK correction, which ablates corneal tissue, femtosecond laser refractive vision correction carves a precisely formed lenticule from the stroma. When the lenticule is removed, the corneal radius of curvature flattens to the desired correction.
The actual procedure is a femto lamellar keratomileusis, more commonly referred to as SMILE, for small incision lenticule extraction. The surgeon cuts a 90° flap into the corneal surface rather than the familiar 270° LASIK flap to access the stroma. The next step is to process the posterior side of the lenticule, then the anterior side. The lenticule is removed, and the correction is complete.
“Thin sections have been tried in the past, but not with the precision of a femtosecond laser,” Dr. Doane said. “This is a kind of back-to-the-future keratomileusis technique, such as automated lamellar keratoplasty. We did remove a lenticule of tissue, but we simply didn’t have the precision with two passes of a microkeratome that we have with a femtosecond laser.”
Reliable extraction of a precise lenticule is only one of the advantages of SMILE over LASIK, he continued. There is no ablation, no plume, and no hydration concerns. The postoperative cornea is slightly prolate. There is no or minimal induction of higher-order aberrations and the potential for aberration-neutral refractive treatments.
This initial prospective trial included 64 eyes in 64 patients. The mean preoperative spherical equivalent was –4.46 D. The mean sphere was –4.39 and the mean cylinder was –0.14. Patients were aged 22 to 59 years (the mean age was 35 years) and had no prior ocular surgery or ocular pathologic diagnoses.
“What we really wanted to see was if this procedure is, in fact, as refractively predictable as LASIK, as stable, as safe, and as effective in vision correction,” Dr. Doane said. “We hit all of our targets and are very excited about these outcomes.”
The mean manifest refraction spherical equivalent 7 days postoperatively was –0.06 (–0.38 to +0.25) and the same at 3 months. Predictability was excellent, with an R2 at 7 days of 0.9901 and 0.9903 at 3 months. About 95% of eyes were within 0.5 D of the target correction at 7 days and at 3 months.
Best uncorrected visual acuity was 20/40 or better for all eyes from day 1 through 3 months. At 3 months, about 95% of eyes were 20/25 or better and 90% were 20/20 or better. Approximately 55% of eyes had unchanged best-corrected visual acuity at 3 months, nearly 30% had gained one line, 5% had gained two lines, and a few eyes had gained two or more lines. A few eyes lost one line and no eyes lost two or more lines at 3 months.
By 1 month postoperatively, all eyes were 20/25 or better, more than 90% were 20/20 or better, half were 20/16 or better, and nearly 10% were 20/12.5 or better.
Patients were more comfortable following SMILE compared with LASIK, Dr. Doane noted. There were fewer reports of dry eye or other discomfort.
“SMILE provides what current techniques don’t-extremely fast visual recovery with preservation of most corneal nerves,” he said. “We anticipate more structural and mechanical stability-what we see with a 270° LASIK flap-while maintaining excellent refractive predictability, efficacy, stability, and quality of vision.”
John F. Doane, MD
Dr. Doane reported financial interests in Bausch + Lomb, Calhoun Vision, and Carl Zeiss Meditec.
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