The femtosecond laser has brought many significant advances to eye surgery. For more than a decade, it has been used to create lamellar corneal flaps for laser in situ keratomileusis (LASIK), and more recently this laser is used to precisely perform several steps in cataract surgery. Additionally, it is used to create matching perforations and buttons in corneal transplant surgeries. The ability of the laser to accurately create a separation in corneal tissue makes it a very versatile laser. We will describe a new application of the femtosecond laser in refractive surgery: a procedure called small-incision lenticule extraction for moderate to high myopia (SMILE).
Currently, LASIK is a two-step procedure in which a femtosecond laser creates a corneal flap and an excimer laser ablates tissue to change the curvature of the cornea, resulting in the desired refractive outcome. SMILE is a one-laser, femtosecond-only procedure. The femtosecond laser creates a lenticule of tissue, which is removed via a “channel” in the cornea, eliminating the flap in the cornea. This procedure is CME approved in Europe and is under FDA investigation in the United States and not yet approved.
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The SMILE procedure
When performing the SMILE procedure, the surgeon applies suction to the eye and “docks” the femtosecond laser. The laser photo-ablates a refractive lenticule with a diameter of 6.0 mm to 6.8 mm at a depth of 100 µm to 120 µm. A single side-cut is made at the superior position, which has a width of 2.5 to 4.0 mm. Once the laser treatment is complete, the surgeon dissects the lenticule through the side-cut with forceps, removing the small piece of corneal tissue. Postoperative treatment includes the use of antibiotics and steroids similar to LASIK.
There are several theoretical advantages of this new procedure. Several of the known complications of LASIK are flap related, such as displaced flap, flap striae, and epithelial ingrowth. While many of these complications are eliminated with a flapless procedure, some cases of epithelial ingrowth have been reported. The procedure is likely to sever fewer corneal nerves—possibly resulting in less dry eye—and the treatment removes less tissue per diopter, allowing for safely treating higher refractive errors and creating more corneal biomechanical stability. Finally, only one laser is used completely to treat the patient; therefore, there may be less capital and per procedure costs to the surgeon and ultimately the patient.