A recent prospective randomized contralateral eye study of LASIK and SMILE found both procedures led to significant epithelial thickening—with a surprisingly similar response between the two techniques, according to the study.

Twenty-one patients had LASIK in one eye and SMILE in the other on the same day by the same surgeon. They were followed for two years post-op and evaluated with corneal epithelial mapping using anterior segment optical coherence tomography (AS-OCT).

From a refractive standpoint, the two procedures were not statistically different, given the target of plano: the average uncorrected distance visual acuity for both groups was 0.02 ±0.07 decimal (20/100 Snellen). While this did not come as a surprise to the researchers, the lack of any statistically significant difference for corneal epithelial thickness was unexpected. Corneal epithelial thicknesses for both groups were statistically significantly different between pre-op measurements and at one, three, six, 12 and 24 months. However, between LASIK and SMILE, the data shows no statistically significant difference.

“These data come as a surprise when considering that LASIK involves a much larger surface intervention than SMILE and intuitively would be suspected to affect epithelial remodeling more,” the study authors wrote.

The researchers did note a slight difference in the epithelial thickness variations between LASIK and SMILE, where eyes that had LASIK showed greater variation in the minimum and maximum thicknesses compared with SMILE eyes. This means “morphologically the epithelium is more homogeneous than in the LASIK group,” the study says. “Although not statistically significant, this difference noted may correlate with the milder transient dry eye period noted in the SMILE eyes.”

“The data presented herein carry the higher reliability of contralateral eye evaluation that may reduce many of the intersubject bias. Nevertheless, the two procedures seemed to affect epithelium remodeling with more similarity than difference,” the study concludes.

Kanellopoulos AJ. Comparison of corneal epithelial remodeling over 2 years in LASIK versus SMILE: a contralateral eye study. Cornea. 2019 Mar;38(3):290-96.