Few Patients Require Enhancement Procedure After SMILE Surgery

With SMILE, 1% to 7% of patients may need enhancement, for which PRK is effective and poses several advantages.

With any type of refractive surgery, there is always a slight chance that further correction will be needed due to residual refractive error, or higher myopic correction and regression — typically, enhancement procedures after small-incision lenticule extraction (SMILE) include photorefractive keratectomy (PRK), laser-assisted in-situ keratomileusis (LASIK), or other techniques. However, a report published in Clinical Ophthalmology shows PRK after SMILE is a safe and effective measure that may best preserve the stromal bed.

Of 405 eyes that underwent SMILE between March 14, 2017 and April 8, 2022 at a single center in Utah, 15 eyes (3.7%) received alcohol-assisted PRK enhancement. The retrospective investigation determined that for patients with 1 year of follow-up, the retreatment rate was 1.3%, and 2-year rate was 7.3%. The average time from initial SMILE to subsequent procedures was 15.9±6.94 months, ranging from 5 to 26 months.

No significant differences appeared in preoperative characteristics between those who needed or did not need enhancement. Mean spherical equivalent (SEQ) was less myopic in patients of the overcorrection subset, but not significantly so (P =.52). Surgeons performed second procedures on 15 eyes (mean patient age 33.82±6.21 years), including 9 eyes with initial spherical undercorrection, 5 with overcorrection, and 1 that was spherically plano.

Outcomes 1 year post-enhancement revealed 87% of eyes displayed uncorrected distance visual acuity (UDVA) of at least 20/20, and 100% with 20/40 or better. Further, 67% were within 0.25 diopters (D) of the goal SEQ, 87% within 0.50 D, and 100% within 1 D. Change from pre- to post-enhancement UDVA was significant (P <.000001). Pre-enhancement mean cylinder of -0.70 D improved to -0.35 D, also a significant improvement (P =.04).

Ophthalmologists who are working with patients seeking enhancement after SMILE should consider the advantages and disadvantages of each retreatment method to ensure high efficacy and safety.

Although the final mean SEQ did not change significantly overall (P =.10), individuals in a negative sphere subgroup meaningfully improved (P =.002), as did those in the positive sphere set (P =.03), according to the researchers. No participant lost any lines of corrected distance visual acuity (CDVA). Safety was computed by dividing the mean post-surgery CDVA by pre-op CDVA, with the resulting index of 0.99.

An advantage of PRK enhancement after SMILE is that it bypasses the biomechanical stress of a flap. LASIK and the circle method may also affect the anterior corneal cap or Bowman’s layer, the study explains. A disadvantage of PRK is the possibility for inflammation and apoptosis — but this risk may be mitigated with mitomycin-C.

“Ophthalmologists who are working with patients seeking enhancement after SMILE should consider the advantages and disadvantages of each retreatment method to ensure high efficacy and safety,” according to the study authors.

SMILE was first approved by the US Food and Drug Administration (FDA) in 2016. Initial studies in 2017 and 2018 reported enhancement rates of from 1.1% to 4.4%. For the current study, in year by year numbers, the rate of 10% in 2019 dropped to 2% for 2020. Although further study is called for, the investigators speculate that outcomes with SMILE are rising.

A small sample and “nonlinear follow-up data” are limits of this analysis. 


Moshirfar M, Parsons MT, Chartrand NA, et al. Photorefractive keratectomy enhancement (PRK) after small-iincision lenticule extraction (SMILE). Clin Ophthalmol. September 12, 2022;16:3033-3042. doi:10.2147/OPTH.S381319