What Is SMILE Eye Surgery?

Medically Reviewed by Dany Paul Baby, MD on June 16, 2022
Written by Parang Mehta
5 min read

More than 150 million Americans have poor vision because of a refractive error. Refractive errors make your vision blurry or hazy, making reading difficult, and can give you eye strain and headaches. You will need prescription glasses or contact lenses to see clearly. SMILE (small incision lenticule extraction) is a surgical procedure that works by reshaping your cornea. This focuses light accurately on your retina, giving you sharp vision. SMILE is a relatively new alternative to the well-established LASIK (laser-assisted in situ keratomileusis) procedure.

SMILE is a type of surgery used to correct refractive errors. The four types of refractive error are myopia (nearsightedness), hypermetropia (farsightedness), astigmatism (blurred vision at all distances), and presbyopia (an inability to focus your eyes up close). 

Your vision depends on your cornea and lens focusing a clear image of the world before you onto your retina. This requires refraction (bending) of light rays to form a sharp image on your retina. This refraction is performed by the cornea and lens. Alterations in the shape of the cornea cause the image on the retina to be unfocused, making your vision blurry.

SMILE surgery changes the curvature of your cornea. This restores refraction to normal, giving you sharp vision again. It reduces the need for glasses or contact lenses. You may even be able to see well without them. SMILE is relatively new. It was approved for myopia correction in 2016 and for astigmatism in 2018.

You should talk with your ophthalmologist about what to expect from this surgery. They'll tell you not to expect perfect vision without glasses or contact lenses. It's possible your vision will improve to that point, but it isn't certain. It's important to have realistic expectations. 

After SMILE surgery, you'll probably be able to perform most tasks without corrective glasses. Your vision will certainly be better. But you may still have to use glasses for some activities, like driving at night or reading.

Almost all people who undergo SMILE surgery achieve visual acuity of 20/40 without glasses or contact lenses. About 88% (7 out of 8) achieve 20/20 vision without glasses or contact lenses.

Before the surgery, your ophthalmologist will perform a complete eye examination. They'll want to ensure you don't have any eye problems, especially the cornea. Some eye disorders can affect SMILE surgery or worsen after surgery. They'll test your vision to make sure it hasn't changed over the past year. It also needs to be within the limits correctable by SMILE.

Your ophthalmologist will also check the thickness of your cornea and take precise measurements. They will then feed these measurements into the computer that guides the SMILE laser.

SMILE is usually carried out as an outpatient procedure. You won't need to stay overnight at the hospital. It's a computer-guided procedure and usually takes about 20 minutes. Both your eyes are treated together.

The procedure is done under local anesthesia. Medicine drops are put into your eyes to make them numb. A femtosecond laser is used to cut a small lens-shaped disc in the cornea. This disc is extracted through a small incision only 2 to 3 millimeters wide. This incision is also created by the femtosecond laser. This procedure reshapes the cornea to exactly reverse the refractive error of the eye.

SMILE surgery is performed under topical (local) anesthesia that numbs your eyes. When the effect of the medicine wears off, you will have some discomfort. Tearing and redness are common. You may also have pain and a gritty sensation that lasts 6 to 12 hours.

SMILE carries the risks of overcorrection or undercorrection. When this happens, you may have to continue wearing glasses or contact lenses. The procedure is generally safe, but you may have corneal abrasions or small tears at the incision site. These complications are minor and don't affect vision long-term.

LASIK has been in use for many years. It provides dependable correction of refraction. Compared to SMILE, LASIK gives better uncorrected visual acuity and low-contrast visual acuity. LASIK is approved for the correction of farsightedness (hypermetropia).

On the other hand, SMILE has quicker recovery from post-procedure dry eyes. Since the incision is small, very few corneal nerves are damaged. Corneal sensation recovers sooner than with LASIK, which lifts a large flap of the cornea, damaging many nerves.

There are some biomechanical advantages to SMILE, since it uses only a small incision. The cornea may retain more of its strength. SMILE may be better for you if you have an active lifestyle. LASIK lifts a large flap of the cornea, which may be dislodged during vigorous activity.

SMILE is also more cost-effective, as it requires only one laser. The femtosecond laser creates both the lenticule and the incision for extracting it. LASIK needs a second laser (an excimer).

Like all surgical procedures, SMILE has some requirements. These make it safe for you and increase the likelihood of success:

  • You should be at least 22 years old.
  • Your vision should be stable. Your eye prescription should not have changed in the past year.
  • Your eyes and corneas should be healthy.
  • Your myopia should be between −1 and −10.
  • Your astigmatism should be less than 3 diopters.

SMILE surgery can correct your vision and free you from the need to wear glasses or contact lenses. But this procedure isn't appropriate for everyone. Some conditions can make you unsuitable for this surgery: 

  • Thin corneas
  • Irregular astigmatism
  • Scars on the cornea
  • Progressive ectasia (thinning of the cornea)
  • Changing (unstable) refraction
  • Cataracts in one or both eyes
  • Glaucoma
  • Diabetes, uncontrolled
  • Earlier eye surgery or disease
  • Pregnancy or breastfeeding

Since SMILE is a fairly new procedure, experience with it is limited. The small incision in the cornea is an advantage. Recovery of corneal sensation is quicker and dry eyes last shorter after SMILE than with LASIK. Currently, the procedure is approved only for myopia and astigmatism. As more trials are completed, the U.S. Food and Drug Administration may approve it for more uses. SMILE has good outcomes and is a useful procedure for vision correction.