Any anterior segment surgery that involves the cornea has the potential to weaken and/or reshape it. Small-incision lenticule extraction (SMILE) either held its own or resulted in better outcomes compared with other corneal refractive surgeries, a study in BMC Ophthalmology reports.

Canadian researchers reviewed 22 investigations conducted from 2005 to 2019 that compared SMILE and other refractive surgeries on adult myopia patients. The studies included five randomized controlled trials, nine prospective and six retrospective cohort studies and two cross-sectional investigations.

The analysis reported corneal biomechanical strength was preserved significantly better after SMILE than femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and LASIK, but was comparable to femtosecond lenticule extraction (FLEX) and the photorefractive keratectomy (PRK)/laser-assisted subepithelial keratectomy (LASEK) group.

Researchers looked at the combined effect of corneal hysteresis and corneal resistance factor and reported the following differences compared with SMILE: FS-LASIK, 0.41; LASIK, 1.31; FLEX, -0.01; PRK/LASEK, 0.26.

However, the study found Corvis ST measurements after SMILE were comparable to FS-LASIK/LASIK.

Investigators noted only a few studies compared SMILE’s corneal biomechanical properties to FLEX, PRK and LASEK. 

“The biomechanical outcomes between SMILE and FLEX were comparable. Although no significant difference was found, PRK/LASEK group showed better outcomes than SMILE,” researchers wrote in their paper.

In a meta-analysis, Corvis ST was not sensitive in detecting the difference of postoperative corneal biomechanical properties between surgeries, they added. As such, more studies are needed to apply Corvis ST on evaluating corneal biomechanics after refractive surgeries, the study noted.

Guo H, Hosseini-Moghaddam SM, Hodge W. Corneal biomechanical properties after SMILE versus FLEX, LASIK, LASEK, or PRK: a systematic review and meta-analysis. BMC Ophthalmol. August 1, 2019. [Epub ahead of print].