Eyeworld

EW REFRACTIVE SURGERY 72 September 2014 by Ellen Stodola EyeWorld Staff Writer SMILE uses femtosecond laser for corneal refractive procedure This new technique offers the option of doing an intrastromal procedure without a fl ap T he SMILE technique is a new method used with the VisuMax 500 kHZ fem- tosecond laser (Carl Zeiss Meditec, Jena, Germany) that provides lenticule extraction without creating a LASIK fl ap. John Doane, MD, Discover Vision Cen- ters, Kansas City, Kan.; and Vance Thompson, MD, Vance Thompson Vision, Sioux Falls, S.D., discussed the procedure, the FDA-monitored trial, and some advantages and disadvantages. What is the SMILE procedure? The acronym SMILE stands for small incision lenticule extraction. "In- stead of creating a fl ap, we make a lenticule of tissue within the stroma with an anterior and posterior pass of the femtosecond laser to create a three dimensional piece of tissue that is manually removed through a 2–3 mm or 60 degree incision at the 7.5 mm optical zone," Dr. Doane said. "The SMILE technique is a 'new age twist' on a previous corneal refractive concept that has been utilize d in the past but abandoned due to better techniques, specifi cally excimer laser refractive procedures." The "new age twist" that Dr. Doane referred to is the use of the femtosecond laser in this technique, and the "corneal refractive concept" is the removal of a convex-shaped lenticule of tissue from within the corneal stroma to fl atten the central cornea and reduce myopia. SMILE requires certain charac- teristics of the femtosecond laser for it to work correctly. Dr. Doane said the laser needs to have a high nu- merical aperture. This means the x, y, and z spot placement of photodis- ruption must be exquisite, he said. "If this is achieved, near perfect depth placement of contiguous spots can occur at the lowest single spot energy, and thus excimer laser-like refractive precision can be achieved." This is a tall order for a femtosecond delivery system, he said. Where do we stand in the FDA trials? SMILE is being studied in the U.S. at 5 centers. In addition to Dr. Thompson and Dr. Doane, the investigational centers are with William Culbertson, MD, and Sonia Yoo, MD, Miami; John Vukich, MD, Madison, Wis.; and Jon Dishler, MD, Greenwood Village, Colo. "Patients enrolled in the study have spherical myopia in the range of –1 to –10 D and up to –0.50 D cyl- inder, although cylinder is not being treated," Dr. Thompson said. SMILE is performed in one eye, and the non-study eye is treated with LASIK. "We have been impressed with the accuracy of the SMILE proce- dure," he said. Preliminary clinical trial results were presented at the 2014 ASCRS•ASOA Symposium & Con- gress, representing data from 315 eyes. So far, refractive predictability has been impressive in the study. Some risks identifi ed were loss of suction and diffi cult lenticule removal without tissue loss with retained tissue. The enrollment goal in the clinical trial is 340 eyes, Dr. Thompson said. Advantages of SMILE Dr. Thompson said that the option of being able to do an intrastromal procedure in one step without a fl ap is exciting. "In general we have the same visual and refractive results as LASIK, but our experience and the literature support less dry eye and improved corneal sensation with the SMILE procedure," he said. The pos- sibility of improved biomechanics is another advantage. "The incision through the epithelium, Bowman's, and the underlying stroma is much smaller compared to the size of the side-cut incision made during LASIK, and thus subsequent foreign body sensation is minimal and transient with the SMILE procedure," he said. The photodisruption with SMILE is also advantageous, Dr. Doane said. "The glaring differ- ence between femtosecond laser photodisruption and excimer laser refractive procedures is that with excimer laser techniques, the cornea stroma being treated is exposed to the environment of open air, so relative humidity, the speed with which the procedure is completed, temperature, barometric pressure, and air purity that the excimer laser beam are exposed to can vary from case to case, surgeon to surgeon, and locale to locale," he said. With the SMILE technique because the photodisruption is done in a relative vacuum intrastromally within the cornea and the epithe- lium is not disrupted, the envi- ronmental factors will not impact outcomes. "This is a signifi cant factor in moderate and higher myopic treatments," Dr. Doane said. Disadvantages of SMILE As this is a new procedure, there are still some issues that need to be O ne of the most exciting new tech- nologies in refractive surgery is the SMILE technique. In this article, two of the leading United States investigators, John Doane, MD, and Vance Thompson, MD, discuss their early experience with SMILE. SMILE is a disruptive technology that will signifi cantly change the way we think about corneal refractive surgery. The small incision should signifi cantly reduce the loss of corneal sensation and dry eye associated with LASIK and PRK. There are several issues that will need to be addressed including how to perform enhancements and whether hyperopia can be treated with the SMILE technique. However, the concept of a corneal refractive surgery performed with only a femtosecond laser and without an excimer is intriguing and exciting. Eric Donnenfeld, MD, refractive editor SMILE procedure (sphere only) Source: Vance Thompson, MD Refractive editor's corner of the world

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