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What is the SMILE procedure, and why don’t you do it?

SMILE is a new procedure that flattens the cornea to reduce myopia (nearsightedness). It can be helpful in rare cases—but it still has some maturing to do.

By Joel Hunter, MD

First off, SMILE probably wins the award for best acronym in refractive surgery. Who doesn’t like smiles? I can’t think of anyone outside of characters from futuristic dystopian films, but they’ve probably figured out a way to cure vision problems so it doesn’t even matter. Here in present day America, people want to smile. Reasons like that make me wish it was a procedure we offered at Hunter Vision. All the other facts about it, though, are enough to tip the scales in the other direction for me. If you skip the rest of the blog, the main reason I don’t want to perform SMILE quite yet is that it’s just not there yet. It hasn’t matured enough. It’s the same reason we don’t offer green bananas or unpopped popcorn kernels for patients to snack on.

SMILE stands for SMall Incision Lenticule Extraction. The use of the capital S and capital M is forgivable and understandable. SILE isn’t going to turn any heads. The way the small incision and lenticule are created is the main gist of the surgery. We’ve had femtosecond lasers for about 15 years now. One day, someone said, “Hey, what if we used the femtosecond laser to do the whole vision correction procedure instead of just to create the flap?” I’d like to imagine his name was Kyle Smile, but I don’t believe it was. Whoever that scientist was, they had a genuinely good idea. SMILE was created as a result of that thought. It turns out, performing vision correction is possible from start to finish with just the laser that normally creates the LASIK flap.

How? It works by accomplishing the same feat that LASIK does. Namely, if someone is myopic, then it’s possible to fix their myopia by flattening their cornea. LASIK does this by using an excimer laser to reshape the cornea. It reshapes the cornea with tiny pulses of invisible light which are able to very precisely remove thousandths of a millimeter of cornea at a time. It is like using the world’s tiniest paintbrush. Femtosecond laser is used to create a flap so the excimer laser can do its tiny paint-brushing work underneath and therefore leave the surface of the eye happy and undisturbed. In SMILE, the cornea is flattened for the same reason, but by a different method.

When a femtosecond laser creates a flap, it does so by placing a plane of microscopic air bubbles in between a couple of layers of corneal tissue. The cornea has layers kind of like an onion, so those bubbles just separate a layer from the one underneath along a natural plane. With SMILE, the same exact thing happens. Except this time, a second plane of microscopic bubbles is placed just above the first one. The layers of cornea in between those two planes of bubbles are now independent. A small sliver of cornea is now free floating (in a very tightly confined area) inside the cornea. That small sliver is called a lenticule (a.k.a. the “L” in SMILE). Now how to extract this lenticule? Well there’s no better way than a SMall Incision right at the border of the lenticule. And so it is removed just as the theoretical Kyle Smile first envisioned.

Removing a tiny sliver of cornea makes it flatter. SMILE works by tailoring the thickness of the sliver to the amount of myopia to be treated. It can treat enormous amounts of myopia, far beyond the safe range for LASIK. It’s because the only incision is small and the rest of the cornea around the removed, round lenticule is left intact. Since the corneal layers at the very front are the strongest ones, leaving all of them almost completely untouched means that a lot of cornea can be removed with minimal impact on its structural integrity.

It’s a very cool idea and it works. The issue keeping me from diving in is that the number of folks for whom it is better than another currently available option (LASIK or ICL) is very small. With LASIK, the sculpting of the cornea—and therefore the quality of vision—is just flat out better. Femtosecond lasers measure depth of treatment about an order of magnitude less precisely than excimer laser. With ICL, very high prescriptions can be fixed without causing severe flattening of the cornea. Again, quality of vision is better in eyes with corneas that maintain their natural shape.

There are some folks for whom SMILE is an option now available where no option was available until now. If you are exceptionally nearsighted and your eye is too small for an ICL, SMILE is worth researching further. If you’re someone who’s a candidate for another procedure, however, my advice would be to choose the option that’s had more time to mature. SMILE will get better over time, just like green bananas do. It may never match the precision of LASIK, but it is a good option for some folks with super high prescriptions, and the range of people for whom it is a reasonable choice will probably grow over time.

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