Eyeworld

EW FEATURE 80 Laser vision correction • February 2018 AT A GLANCE • Patients with abnormalities of wound healing may not be good candidates for LASIK or PRK. • Each procedure has contraindica- tions, so it's important to determine which to use on a case-by-case basis. • Recent advances have helped to optimize the procedures. Use of the femtosecond laser has helped make LASIK flaps easier. Options for adjusting the laser parameters and less laser energy with SMILE are starting to be used. Potential new gels could help address the issue of visual recovery with PRK. by Ellen Stodola EyeWorld Senior Staff Writer that there will be an increase in the procedure. As surgeons adapt and become more comfortable with SMILE, Dr. Durrie also expects to see an increase. He added that SMILE can't correct higher order aberrations, and it can't do asymmetric astigmatism. Therefore, there will still be some decision making. Wavefront-guided versus wavefront-optimized in PRK and LASIK Dr. Doane said that both wavefront- guided and wavefront-optimized can work well. "I am a proponent of wavefront-optimized treatments for all patients. There may be select patients in whom a wavefront-guid- ed treatment is beneficial, but they are few and far between," he said. The real issue is the potential for a guided treatment to correct irregu- lar astigmatism, and the results are marginal to date, he said. When comparing wavefront- guided vs. wavefront-optimized, Dr. Wilson said it's more of a ques- tion of which laser is being used. For example, with the VISX laser (Johnson & Johnson Vision, Santa Ana, California) he will usually use wavefront-guided. It's sometimes possible that despite a double check, the wavefront analysis will not cor- respond to the manifest refractions, and in these cases, he will take a traditional approach based on their refractions. Someone using the Allegretto laser (Alcon, Fort Worth, Texas) would use wavefront-optimized, as this laser cannot do wavefront-guid- ed in the U.S. Dr. Wilson said that wavefront- driven ablations use more tissue per Surgeons discuss the three procedures and other considerations in corneal refractive surgery D epending on the patient, SMILE, PRK, and LASIK can all be excellent sur- gical choices in corneal refractive surgery. Steven E. Wilson, MD, Cleveland Clinic, Daniel Durrie, MD, Durrie Vision, Overland Park, Kansas, and John Doane, MD, Discover Vision Center, Kansas City, Missouri, discussed how they choose among these procedures depending on different patient char- acteristics and factors. Choosing the procedure Dr. Wilson said that while he enjoys using the Zeiss laser (Carl Zeiss Med- itec, Jena, Germany) to make flaps for LASIK, he is not particularly a fan of SMILE. Though he initially in- tended to transition to using SMILE in his practice, he became less inclined to use it the more familiar he became with the procedure and results. For patients with less corneal thickness than is needed for the lev- el of correction, Dr. Wilson thinks PRK works well without the added surgical time associated with SMILE or the increased potential for prob- lems or enhancements. Compared to LASIK, SMILE eyes have delayed visual recovery, Dr. Wilson added. When you make a single cut with a femtosecond laser to make a flap for LASIK, no two cuts are the same, Dr. Wilson said. "LASIK is forgiving, and irregularities in the femto cut will line up if the flap is returned to the original position," he said. However, when you make a second cut with the femto laser for SMILE and pull out a lenticule, since no two femtosecond laser cuts are the same, those two surfaces with differing irregularities cannot go back together precisely; resulting irregularities are not masked and are often transmitted to the anteri- or corneal surface. It takes time for stromal remodeling to then reduce the irregularities of these superim- posed different surfaces. Dr. Wilson has had a few pa- tients ask about the SMILE proce- dure. If they're really interested, he will refer them to his colleague, Ronald Krueger, MD, who does per- form SMILE in a small proportion of his patients. Dr. Wilson said 80% of his patients have LASIK. "I think it's a wonderful procedure as long as the patient doesn't have any contraindi- cations," he said. Contraindications include inferior steepening of cor- neal topography that is deemed not to be keratoconus, corneal thickness too thin for the level of correction, anterior basement membrane dys- trophy (ABMD), and anterior scars in the stroma. Dr. Doane said that he will default to PRK if forme fruste kera- toconus type topography is noted. "If someone has keratoconus, I am educating on the role of corneal crosslinking," he said. "Additional reasons to favor PRK are if the cor- nea is thinner than 500 microns or the central corneal power is greater than 46.5 D." Along with form fruste keratoconus, a thin cornea, and central power >46.5, he will opt more aggressively for PRK if these findings are in a person younger than 25, Dr. Doane said. "PRK, LASIK, and SMILE can work equally well for a given re- fraction barring issues of potential ectasia," Dr. Doane said. "If some- one is involved in contact sports or a profession with the risk of physi- cal contact, I would opt for SMILE or PRK." All of the procedures work, Dr. Durrie said, adding that it's all about which procedure is best for each patient. He said that he's a supporter of all three. When patients come in, Dr. Durrie will do a full exam, including in-depth analysis of topography, higher order aberrations, and de- termine if the patient is a spherical myope. "If the patient is a spherical myope, all three procedures are in play," he said. He will look at factors like cor- neal thickness and corneal curvature and see if there's a reason to do PRK. "If they can have LASIK or SMILE, I have a tendency to lean toward SMILE," he said. Dr. Durrie noted his clinical results have shown that patients who are higher myopes have better results with SMILE. If SMILE is ap- proved for astigmatism, he expects Choosing SMILE, PRK, or LASIK continued on page 82 Illustration of the two SMILE femtosecond cuts differing and creating irregularity that is often transmitted to the anterior corneal surface Source: Steven E. Wilson, MD

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