February 2018

COVER FEATURE

Laser vision correction
Choosing SMILE, PRK, or LASIK


by Ellen Stodola EyeWorld Senior Staff Writer

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


Comparison of PRK, LASIK, and SMILE
Pravin Vaddavalli, MD, compares various refractive procedures like PRK, LASIK, and SMILE.

Surgeons discuss the three procedures and other considerations in corneal refractive surgery 

Depending on the patient, SMILE, PRK, and LASIK can all be excellent surgical 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 characteristics and factors. 

Choosing the procedure 

Dr. Wilson said that while he enjoys using the Zeiss laser (Carl Zeiss Meditec, Jena, Germany) to make flaps for LASIK, he is not particularly a fan of SMILE. Though he initially intended 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 level of correction, Dr. Wilson thinks PRK works well without the added surgical time associated with SMILE or the increased potential for problems 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 anterior corneal surface. It takes time for stromal remodeling to then reduce the irregularities of these superimposed different surfaces. 

Dr. Wilson has had a few patients ask about the SMILE procedure. If they’re really interested, he will refer them to his colleague, Ronald Krueger, MD, who does perform 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 contraindications,” he said. Contraindications include inferior steepening of corneal topography that is deemed not to be keratoconus, corneal thickness too thin for the level of correction, anterior basement membrane dystrophy (ABMD), and anterior scars in the stroma. 

Dr. Doane said that he will default to PRK if forme fruste keratoconus 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 cornea 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 refraction barring issues of potential ectasia,” Dr. Doane said. “If someone is involved in contact sports or a profession with the risk of physical 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 determine 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 corneal 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 approved for astigmatism, he expects 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-guided treatment is beneficial, but they are few and far between,” he said. The real issue is the potential for a guided treatment to correct irregular 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 question of which laser is being used. 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 correspond to the manifest refractions, and in these cases, he will take a traditional approach based on their refractions. 

The WaveLight Allegretto Wave laser (Alcon, Fort Worth, Texas) is able to do wavefront-guided and wavefront-optimized treatments. 

Dr. Wilson said that wavefront-driven ablations use more tissue per diopter of correction. If the patient is borderline in corneal thickness compared to the correction given, he will do the procedure traditional to spare some of the stroma. 

Dr. Durrie likes to analyze a Pentacam (Oculus, Wetzlar, Germany) picture, and if he finds that the patient has asymmetric astigmatism, he will choose either wavefront-guided or topography-guided. 

Corneal wound healing 

Dr. Wilson said that patients who have abnormalities of wound healing are not good candidates for LASIK or PRK. If patients have ABMD, they are better treated by surface ablation because you allow the basement membrane to regenerate, he said, adding that it could take a few years to reacquire the changes of the duplicated basement membrane. 

Otherwise, Dr. Wilson said that wound healing issues don’t commonly drive his choice between LASIK and PRK. This decision is based more on corneal topography, thickness, etc. 

“It’s gotten fairly simple now because you have to maximize patients’ tear film and meibomian glands beforehand,” Dr. Durrie said. Postoperatively, his practice follows their own patients, so if there’s something going on, it can be treated immediately. “As far as medications are concerned, we’re using the same medications on all three,” he said. This includes antibiotics for a week and steroids for a week, 4 times a day. This regimen is tapered down depending on any preoperative conditions. 

Dr. Doane thinks that it is important to understand the massive improvement in outcomes with the advent of optimized treatment patterns that enlarged the short axis of astigmatic treatments, which diminished night symptoms and minimized regression of astigmatic correction. “It is also important to realize that a 6-mm ablation zone for excimer laser ablations, if well centered, is an optimal trade-off of preventing night symptoms and minimizing ‘shrinkage’ of the effective optical zone on topography, as was seen with early 4–5 mm ablation zones of the mid 1990s performed internationally,” Dr. Doane said. 

Recent advancements 

Dr. Doane said that the one area that is seeing relatively quick advancements is SMILE. “One of the early knocks on SMILE was slow vision recovery,” he said. “This was the case with femtosecond lenticule extraction where a LASIK-like flap was created and the lenticule was pealed from the stromal bed,” he said. 

Over the past 12–24 months it has become clear how important spot and track spacing and energy optimization are for quick recovery of vision essentially equal to LASIK postop day 1 outcomes, Dr. Doane said. “Since FDA approval, we have been lowering energy settings and cannot wait until we can increase our current spot and track spacing of 3.0 microns to upward of 4.5 microns,” he said. “Not only will the dissection of the lenticule be improved, but excellent postop day 1 visual acuities will be expected and achieved.” 

Dr. Durrie noted that there may be some new gels coming, which could aid in faster visual recovery for PRK patients. “PRK is a good procedure, it’s just the slow visual recovery that throws it off,” he said. 

As far as SMILE, Dr. Durrie said the most important thing is getting the technique down. He noted that internationally, some surgeons have been able to adjust some of the laser parameters and make the cuts smoother with less laser energy. “Being able to upgrade to this would be great,” he said, adding that it would also be beneficial to eventually be able to reach in and take the lenticule out without having to dissect at all. 

With LASIK, Dr. Wilson noted that the biggest change was the femtosecond laser for making flaps. He used the microkeratome for many years before, and he was always concerned about the potential for buttonholes and other complications. “It doesn’t even enter my mind anymore with the femtosecond laser,” he said. Occasionally, he will have an issue with the laser, like in one quadrant where the side cut won’t be complete. “But most of those, I can release with a lamellar dissecting blade and go ahead with the procedure,” he said. 

As far as PRK, Dr. Wilson said the biggest advance has been the use of mitomycin-C to limit haze. The remaining frontier in PRK is the discomfort that patients experience for 2–3 days, he added. 

Editors’ note: Dr. Durrie has financial interests with Alcon and Johnson & Johnson Vision. Dr. Doane has financial interests with Carl Zeiss Meditec. Dr. Wilson has no financial interests related to his comments. This article was updated on April 3 to correct an error. 

Contact information 

Doane: jdoane@discovervision.com 

Durrie: ddurrie@durrievision.com 

Wilson: WILSONS4@ccf.org

Choosing SMILE, PRK, or LASIK Choosing SMILE, PRK, or LASIK
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