At A Glance
- Studies have shown long-term safety and stable visual outcomes with small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism to be comparable with those for LASIK.
- To offer patients thorough education regarding surgical options for laser vision correction, optometrists must understand this new modality.
- Indications for SMILE were expanded last year to include myopic astigmatism in addition to myopia.
The landscape of corneal refractive surgery continues to change—even the traditional procedures that have established records of safety and predictability. It is important to present all options, both surgical and nonsurgical, to patients seeking correction of refractive error. Proactively educating your patients on the options to correct refractive error establishes you as the quarterback of their care and helps to cement the collaborative care model if the patient chooses a surgical option.
Recent studies have shown long-term safety and stable visual outcomes with small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism to be comparable with those for LASIK.1,2 With the entry of SMILE into the mix of corneal refractive surgery options, optometrists must understand this new modality in order to properly educate our patients on all of their options.
WHAT IS SMILE?
In SMILE, the surgeon uses the VisuMax femtosecond laser (Carl Zeiss Meditec) to create a series of corneal lamellar resections that define the posterior surface, side cut, and anterior surface of a corneal lenticule. The laser also creates a superior corneal incision through which the surgeon removes the lenticule. After lenticule removal, the anterior cornea settles onto the newly created curvature, correcting the refractive error.
SMILE was approved by the FDA in 2016 to correct spherical myopia with less than 0.50 D of astigmatism. Potential candidates were limited due to the sphere-only indication. In October 2018 the FDA approved an expansion of the indication for SMILE to include the correction of myopic astigmatism. This has made SMILE an option for a larger segment of patients who want refractive corneal surgery.
Current indications are for the treatment of patients aged 22 years and older who have myopia with or without astigmatism: myopia from -1.00 D to -10.00 D and astigmatism from -0.75 D to -3.00 D with a maximum spherical equivalent of -10.00 D.
WHO IS A CANDIDATE?
Myopic patients should be educated equally on all options for corneal refractive surgery including LASIK, PRK, and SMILE. As with any new technology, some savvy patients will come in requesting only SMILE, believing that this new option may be a better form of laser vision correction. Most patients, however, are still unaware of SMILE as an option. There is such strong familiarity now with LASIK and PRK. Everyone knows someone who has had LASIK.
We educate our patients that these three procedures are complementary to each other. The choice of one over the others does not involve a competition among surgeries, but rather an evaluation of what is the best procedure for a particular patient’s eyes and vision. The same criteria that make a patient a candidate for LASIK also make him or her a candidate for SMILE.
Patients should have good ocular health and stable refractions. Their corneas should not be thinner than average and should not have anterior basement membrane dystrophy or suspicious or irregular topography. We look for and aggressively treat dry eye, meibomian gland dysfunction, and blepharitis prior to surgery.
As with all refractive procedures, patients must have realistic expectations for outcomes, must be informed of potential complications, and must understand presbyopia and the lenticular changes that will eventually occur in their eyes.
I tend to describe LASIK and PRK first to patients who are good candidates. I then describe SMILE. I explain that, in SMILE, we use the same laser that makes the flap in LASIK to focus into the cornea and create a lens or lenticule of tissue equal to the size of the correction needed. The laser makes a small incision at the top of the cornea, and the surgeon then removes the lenticule through that incision. The cornea then flattens onto the new curvature to correct vision.
Most patients perceive this description as equally creepy and cool. However, because the recovery time and return of vision with SMILE are similar to those of LASIK, patients are relieved—or at least intrigued—especially if they were hoping not to have PRK.
WHICH PROCEDURE FOR MY EYES?
When patients are considering SMILE, the following pearls can help educate them to make the best decision for their eyes.
Dry Eye Symptoms After Surgery
SMILE can be an advantage for patients with dry eyes. The anterior cornea and nerves are less disrupted by the sidecut, which is 80% smaller than the flap in LASIK. This can reduce postoperative dry eye symptoms and loss of corneal sensitivity in comparison with LASIK, as has been shown in clinical trials.3,4
Low Astigmatism and Low Myopia
Although SMILE is approved to treat -0.75 D to -3.00 D of astigmatism, it won’t treat 0.50 D of astigmatism or less. Some patients will notice a much better image quality with 0.50 D of astigmatism corrected. It’s best to check patients’ image quality during refraction or with a trial frame to see if they like that 0.50 D of cylinder. If so, LASIK or PRK may be the preferred treatment method.
Low myopic corrections with SMILE are actually more difficult technically in surgery. The lenticule is thinner in low corrections, especially less than -1.50 D of myopia, and more prone to tearing during removal.
Centration and Enhancements
Perfect centration of the lenticule is vital to achieving accurate correction with SMILE. Because the suction of the curved applanation cone is fairly light, it is comfortable for the patient, but this can lead to loss of suction, especially with a patient who squeezes his or her lids or moves a lot. We instruct patients that, if we cannot achieve good suction and centration with the VisuMax laser for SMILE, we may have to switch to LASIK.
Although the enhancement rate for SMILE is comparable to that for LASIK and PRK,1,5 SMILE is not used as an enhancement option. The preferred method to enhance after SMILE is PRK, but some surgeons use a LASIK technique. Patients must be informed preoperatively of the options for enhancement if one is needed.
After SMILE, patients are handled very much like post-LASIK patients. They are placed on an antibiotic and steroid drop four times daily for 1 week and are seen at 1 day, 1 week, 1, 3, and 6 months, and 1 year.
Corneas are quite clear after surgery (Figure), and comfort is good. Many patients have little to no foreign body sensation or light sensitivity. Patients also like that the recovery of vision is fast, although it tends not to be as sharp at day 1 as typically reported with LASIK. We have found that vision is comparable to LASIK by 1 to 2 weeks postoperative and averages 20/25 at day 1.
VA and manifest refraction are monitored from 1 week forward, and enhancements can be considered within 3 to 6 months postoperative.
SMILE IS HERE TO STAY
The management of myopia and astigmatism with SMILE will become more common over time, and more patients will be asking about it. The advantages of excellent visual results, patient comfort, fast visual recovery, and reduced dry eye symptoms will drive patients to consider SMILE. For the time being, LASIK and PRK continue to be the only treatments for hyperopia, high astigmatism, wavefront-guided correction of higher-order aberrations, and topography-guided laser treatments.
There are now three options for many patients seeking to reduce their dependence on optical devices: LASIK, PRK, and SMILE. Optometry is uniquely positioned to educate patients on all options for the correction of refractive error, and optometrists will continue to take part in the collaborative care of patients after they undergo laser vision correction, whether LASIK, PRK, or SMILE.
1. Blum M, Taubig K, Grohn C, Sekundo W, Kunert KS. Five year results of small incision lenticule extraction (ReLEx SMILE). Br J Ophthalmol. 2016;100(9):1192-1195.
2. Yan H, Gong LY, Huang W, Peng YL. Clinical outcomes of small incision lenticule extraction versus femtosecond laser-assisted LASIK for myopia: a meta analysis. Int J Ophthalmol. 2017;10(9):1436-1445.
3. Cai WT, Liu QY, Ren CD, et al. Dry eye and corneal sensitivity after small incision lenticule extraction and femtosecond laser assisted in situ keratomileusis: a meta analysis. Int J Ophthalmol. 2017;10(4):632-638.
4. Xu Y, Yang Y. Dry eye after small incision lenticule extraction and LASIK for myopia. J Refract Surg. 2014;30(3):186-190.
5. Hersh PS, Fry KL, Bishop DS. Incidence and associations of retreatment after LASIK. Ophthalmology. 2003;110(4):748-754.