Study: Low-Energy SMILE Day 1 Outcomes Comparable With LASIK

New Vision clinic, main center for refractive surgery in France, with cutting-edge technology for all eye laser operations. Eye operation using the SMILE, Small Incision Lenticule Extraction, laser technique. It is a new generation of treatment which enables short-sightedness to be corrected without removing the superficial layer of the cornea, nor opening it. The SMILE technique involves producing with the Femtosecond laser, a lenticule, thin slice, in 3D in the thickness of the cornea, and removing it with a micro incision in the shape of a smile. The worse the short-sightedness, the thicker the lenticule. (Photo by: BSIP/Universal Images Group via Getty Images)
Researchers compared records of patients who underwent low-energy SMILE, high-energy SMILE and FS-LASIK.

Patients who underwent low-energy (LE) small-incision lenticule extraction (SMILE) had visual acuities on postoperative day (POD) 1 statistically similar to patients who underwent wave-front optimized femtosecond laser–assisted laser in situ keratomileusis (FS-LASIK), and significantly better than high energy (HE) SMILE, researchers found in Journal of Cataract & Refractive Surgery study. LE-SMILE also caused less induced spherical aberration (SA) compared with FS-LASIK.

Adoption rates of SMILE in the United States have been dampened by reports that its POD1 visual acuity are lower than that of LASIK, and conflicting reports on whether SMILE or LASIK induces more higher-order aberrations (HOAs) have been published. Following the FDA’s approval of new indications for SMILE and new parameters for laser settings that allow LE deposition to the cornea (LE SMILE), the researchers sought to address surgeons’ apprehension by comparing the early visual acuity results of LE SMILE with the previous settings (HE SMILE) and with FS-LASIK.

They reviewed medical records of patients who had SMILE (LE or HE) or FS-LASIK for surgical correction of myopia or myopic astigmatism performed by 1 surgeon. Patients with other ocular diseases, abnormal topography, or preoperative corrected distance visual acuities were excluded from the study.

Patients who preferred the full cylinder correction or had topographic cylinder greater than 0.5 D in the same axis of the manifest axis received LASIK while the others received LE SMILE (125-130 nJ energy per spot, 4.5 mm spot spacing, 24 to 25 seconds under the femtosecond laser) or HE SMILE (125 nJ energy per spot, 3.0 mm spot spacing, 38 to 40 seconds under the laser). Each group featured 49 eyes. Astigmatic attempted correction eyes were 1:1 matched between the FS-LASIK and the LE SMILE groups but not between the HE SMILE group due to approval timing of cylinder treatment and wider spot spacing.

Mean uncorrected distance visual acuity (UDVA) at POD1 was -0.003 logMAR for the LE SMILE group, 0.141 logMAR  for the HE SMILE group (P <.0001), and -.011 for the FS-LASIK group (P =.498). Only 18/49 (37%) of HE SMILE patients had 20/20 vision or better on POD1 compared with 45/49 (92%) and 44/49 (90%) in the LE SMILE and FS-LASIK groups, respectively. All FS-LASIK and LE SMILE patients had 20/30 vision or better on POD1. There was also significantly less induction of SA in eyes that of the LE SMILE group compared with the HE SMILE (P =.02) or FS-LASIK (P =.03).

“It is important to note that SMILE is a very different procedure from LASIK and uses much lower FS energy settings to create the lenticule than what is used to create the LASIK flap,” the researchers report. “Accordingly, it is imperative that the energy settings be carefully optimized.”

Limitations of the study include the reporting of outcomes out to 1 month postoperatively.

Disclosure: One author declared affiliations with the biotech or pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Hamilton DR, Chen AC, Korrami R, et al. Comparison of early visual outcomes after low-energy SMILE, high-energy SMILE, and LASIK for myopia and myopic astigmatism in the United States. J Cataract Refract Surg. 2021;47(1):18-26. doi:10.1097/j.jcrs.0000000000000368.