Comparative Study of Primary SMILE, SMILE Enhancement, and Femtosecond Laser–Assisted LASIK on Higher Order Aberrations and Corneal Densitometry

Purpose: To compare differences in corneal densitometry (CD) and higher order aberrations (HOAs) in eyes that underwent small incision lenticule extraction (SMILE) and femtosecond laser–assisted laser in situ keratomileusis (FS-LASIK) for the treatment of myopia and myopic astigmatism at postoperative months 3, 6, and 12, and to evaluate their changes in a separate cohort of eyes after SMILE enhancement. Methods: In this prospective, randomized, paired-eye clinical trial, consecutive eligible participants were randomized to undergo SMILE or FS-LASIK in either eye. Main outcome measures were CD and HOAs preoperatively and at 3, 6, and 12 months postoperatively. A separate cohort of consecutive patients who had SMILE and underwent enhancement were also included for comparison. Results: For CD, no significant differences were found between SMILE and FS-LASIK up to month 12. For HOA measured by wavefront aberrometry, both SMILE and FS-LASIK had an increase in total root mean square (RMS) HOAs, spherical aberration (SA), and vertical coma up to month 12. SMILE had an additional increase in vertical quatrefoil, and FS-LASIK had an increase in horizontal coma at month 12. FS-LASIK had higher SA than SMILE, whereas SMILE had higher vertical quatrefoil than FS-LASIK at month 12. Central and posterior zone CD had significantly decreased after SMILE enhancement compared to after primary SMILE up to 2 years after enhancement. RMS HOAs, lower order aberrations, and SA were all increased after SMILE enhancement compared to after primary SMILE. Conclusions: SMILE induced lower SA but higher vertical quatrefoil than FS-LASIK at 1 year. Both SMILE and FS-LASIK had similar increases in RMS HOAs and vertical coma up to 1 year. There were no differences in CD between both groups. SMILE enhancement additionally had decreased central and posterior CD but greater RMS HOAs and SA compared to primary SMILE. [ J Refract Surg . 2024;40(5):e291–e303.]