Often, when a difficult problem is finally solved, it turns out that the solution isn’t only effective—it’s elegant as well, unburdened by unnecessary complexity. For the problem of refractive errors, LASIK remains the most elegant solution, in addition to being very safe and effective. This is why SMILE’s overly complicated approach to treating refractive errors falls short in comparison. Here, I’ll explain why I choose LASIK for my refractive patients.
Before I delve into the reasons why SMILE isn’t as good as LASIK, I want to say that I’m a big fan of the Zeiss
VisuMax laser, and it’s my favorite flap-making laser for LASIK procedures.
That said, I’m not a fan of SMILE. I’ve come to this opinion by monitoring the ophthalmic literature since the procedure was first released. Also, we have the VisuMax in our facility, and one of my partners has been performing SMILE for a couple of years, so I’ve observed the procedure’s results. Here are the issues with SMILE that I’ve noticed.
• It’s more difficult to do. The first, and one of the more important, things I’ve noticed through this observation is that LASIK is a much simpler procedure than SMILE. Because of SMILE’s complexity, you’re much more likely to end up with a problem during surgery. There were even some papers published about how to handle retained lenticules that were either not fully cut by the laser or were torn during the extraction process, trapping a lenticule fragment within the interface. This fragment then has to be removed or the patient will have severe irregular astigmatism. This increased difficulty is one of my major concerns as SMILE seeks acceptance among a wider audience of ophthalmologists.
• SMILE cuts introduce variability. Another one of the major differences between the two procedures is that, when you make a cut with the femtosecond, no two cuts are the same. I’ve used the IntraLase, the Alcon LenSx and the VisuMax, and they all have this issue; when you cut across the cornea to make the LASIK flap, they can skip a spot here or there in a random way or produce other small imperfections. So, when you lift the flap, you notice slight irregularity in the bed. LASIK, however, is very forgiving of this, because as long as you return the flap to its original position, those irregularities are masked and not reflected in the optical surface. Therefore, they don’t affect the patient’s vision.
When you make the two femtosecond cuts necessary to create the lenticule in SMILE, however, you now have two femtosecond-cut surfaces that no longer match up. Then, when you extract that piece of cornea and the two mismatched surfaces are pressed together, they don’t match. That’s what produces the irregularities that result in patients having a delayed visual recovery with SMILE compared to LASIK (LASIK patients see clearly almost immediately, compared to a several-day delay with SMILE reported in several studies).
• More manipulation, more irregularities. It’s not just the laser cuts that introduce vision-affecting irregularities, it’s the extra mechanical manipulation, as well: Once the lenticule is cut by the two laser passes, you still don’t have a free lenticule. Instead, you now have to use a second instrument in the interface, a spatula, both anterior and posterior to the lenticule, to physically break the remaining adhesions between the lenticule and surrounding cornea. By doing that, you induce even more irregularity.
The reason SMILE patients take longer than LASIK patients to recover vision, Dr. Wilson says, is because the interfaces in SMILE don’t line up when the lenticule is removed, resulting in irregularities.
• The femtosecond is less precise than the excimer. Piggybacking on the previous points, Zeiss will probably say that it has a new spot distribution coming out that will help with the problem of the surface irregularities—and it might—but the irregularities will still be a problem, even with a new spot distribution. Why? Because the femtosecond just doesn’t have the inherent accuracy and precision of an excimer laser: The original IBM researchers who studied the early excimer lasers actually used one to carve the IBM logo onto a human hair—no femtosecond laser will ever match that precision. As a result, SMILE will always have a slower visual recovery, and much less of a “wow” factor, than LASIK.
• Enhancement questions. The flip side to the elegant solution referenced earlier is the problem with multiple solutions; this usually means none of them is ideal. This is the current situation with SMILE enhancements.
LASIK is very easy to enhance. If you perform the enhancement within the first postop year, you can lift the flap without much difficulty and apply additional excimer laser to fine-tune an under- or overcorrection, or treat a little induced astigmatism. With SMILE, though, no one has agreed on the best way to perform a retreatment if the primary procedure gets an undesirable result. You either have to do a surface ablation or try to convert the SMILE to a LASIK, and the company’s actually designed an algorithm to do that. At our facility, we found the SMILE enhancement rate to be higher than LASIK’s, because it’s just not as precise. There’s also the impression a patient gets if he needs an enhancement: Preop, the patient was no doubt told the purported advantages of SMILE over PRK and LASIK, only to find out that, six months later, he needs PRK or LASIK to correct his SMILE procedure that came up short. This isn’t an enjoyable conversation to have.
• SMILE takes more time to do. With all the tissue manipulation involved with SMILE, it ends up taking twice as long as LASIK. This is the last thing a busy surgeon wants to hear. Adding that extra surgery time is a very big deal for the refractive surgeon, because you only have so many surgery slots during a day. If you’re occupying two spots instead of one, you cut down on your productivity, and productivity is a big part of having a successful refractive practice.
• SMILE misses out on surgical advances. About 10 years ago, every other paper presented at the AAO and ASCRS was about the importance of wavefront-driven ablations in LASIK and their ability to reduce visual aberrations. More recently, companies like Alcon have introduced topography-driven ablations and highlighted some of the better results that can be achieved with that technology. Unfortunately, you can’t use either of these approaches with SMILE. So are we suddenly saying that all of that development wasn’t important? On the contrary: Eighty percent of my LASIK patients have wavefront-driven ablations done with the excimer laser.
Unmatched precision: The excimer laser was once used to carve the IBM company logo onto a human hair. The femtosecond is incapable of such feats, Dr. Wilson says.
• There’s still ectasia with SMILE. One of the advantages touted for SMILE is biomechanical superiority compared to LASIK, with proponents specifically saying it leaves the anterior cornea basically untouched. This, they say, makes it less likely for patients who have abnormal corneal topography or thin corneas to develop ectasia after SMILE vs. LASIK for the same level of myopia correction. However, there are now several papers from surgeons who’ve used SMILE in place of LASIK for these questionable cases that subsequently developed ectasia.1 Though, theoretically, there may be some biomechanical advantage to SMILE, someone performing the procedure has to be very careful about assuming he’s going to have an advantage in treating those cases with inferior steepening or low corneal thickness, because it could be a trap. Surgeons now recommend using the same screening criteria for SMILE as LASIK when it comes to ectasia risk.
The other biomechanical argument is that there’s no risk of postop flap dislocation with SMILE. Theoretically, this is the case. However, I’ve only encountered one dislocated flap in the 23 years I’ve been doing LASIK. The large-scale data from the military supports this, as the service now allows soldiers and sailors to undergo LASIK due to the real incidence of late flap dislocations being so low.2,3 In theory, a flap could be truncated by a severe enough blow, such as a car’s airbag deploying, but typically that sort of force would be so powerful that it would risk damage to the cornea even if the patient had had SMILE, or no surgery at all.
• Dry-eye considerations. Though it may be true that there’s less dry eye with SMILE than LASIK, I think that given the thin flaps used with today’s LASIK procedure, we don’t have as much of a dry-eye problem as we did in the past. This is especially true if we pretreat patients prior to LASIK with medications like Restasis and other measures—which you’d want to do anyway with SMILE. In my practice, where I do a lot of LASIK and PRK, dry eye isn’t that much of an issue when appropriate precautions are taken.
So, considering all of the reasons listed above, as well as the great outcomes my patients enjoy after LASIK, I’m confident in choosing it over the newcomer, SMILE. REVIEW
Dr. Wilson is a professor of ophthalmology, director of corneal research, as well as the staff of the refractive surgery and cornea sections of the Cleveland Clinic’s Cole Eye Institute.
1. Moshirfar M, Albarracin JC, Desautels JD, Birdsong OC, Linn SH, Hoopes PC Sr. Ectasia following small-incision lenticule extraction (SMILE): A review of the literature. Clin Ophthalmol 2017;15;11:1683-1688.
2. Tanzer DJ, Brunstetter T, Zeber R. Laser in situ keratomileusis in United States naval aviators. J Cataract Refract Surg 2013 Jul;39:7:1047-58.
3. Warfighter Refractive Eye Surgery Program Overview. https://www.crdamc.amedd.army.mil/surgery/lasik.aspx. Accessed 10 January 2019.