Small Incision Lenticule Extraction (SMILE) Versus Laser Assisted Stromal In Situ Keratomileusis (LASIK) for Astigmatism Corrections: A Systematic Review and Meta-analysis

center dot PURPOSE: To compare small incision lenticule extrac-tion (SMILE) and laser assisted stromal in situ ker-atomileusis (LASIK) for astigmatism correction.center dot DESIGN: Systematic review and meta-analysis center dot METHODS: We reviewed published studies comparing outcomes after LASIK and SMILE for astigmatism cor-rection by querying PubMed, EMBASE, Cochrane, and Web of Science, with a cut-off date of September 3, 2022. We also compared the changes in visual acuity, refrac-tion, and high-order aberrations between the surgeries. Astigmatism correction outcomes in the low-to-moderate group (less than or equal to-2.00 D) and high group (greater than-2.00 D) were evaluated using vector anal-ysis. The Cochrane risk of bias tool in RevMan soft-ware was used for randomized studies (RCT), and Risk Of Bias In Nonrandomized Studies -of Interventions (ROBINS-I) was used for the nonrandomized studies (NRSs).center dot RESULTS: There were 17 studies (5 randomized stud-ies and 12 cohort studies), including 1,985 eyes. A sta-tistically significant difference was found in the correc-tion index (mean difference [MD] =-0.02, 95% con-fidence interval [CI] =-0.04 to-0.01, P= 0.01), al-though there was no significant difference in the in-dex of success (MD = 0.01, 95% CI =-0.03 to 0.05, P= 0.51), different vector (MD = 0.07, 95% CI = 0.00 to 0.13, P= 0.04), and angle of error (MD = 0.56, 95% CI =-0.34 to 1.45, P = 0.22) be-tween SMILE and LASIK. However, for low-to-moderate astigmatism correction, SMILE exhibited a smaller cor-rection index (MD =-0.08, 95% CI =-0.13 to-0.02, P= 0.008) and a larger difference vector (MD = 0.18, 95% CI = 0.09 to 0.27, P <0.0001) than LASIK. There was no significant difference between the differ-ent procedures in visual acuity and refraction (spher-ical equivalent: MD =-0.04, 95% CI =-0.08 to 0.01, P = 0.15) or high-order aberration (MD =-0.01, 95% CI =-0.07 to 0.04, P= 0.67), except spherical aberration (MD =-0.12, 95% CI =-0.23 to-0.01, P= 0.04). The risk of bias was moderate in most stud-ies because of poor reporting of several bias domains for RCTs, and because of confounding and selective outcome reporting for NRSs.center dot CONCLUSIONS: When used to treat severe astigma-tism, both SMILE and LASIK provide effective and pre-dictable results and generally have equivalent outcomes. However, evidence reveals a tendency toward undercor-rection in the SMILE groups for astigmatism correction. In addition, LASIK has a greater probability of causing postoperative spherical aberration. (Am J Ophthalmol 2023;247: 181-199.(c) 2022 Published by Elsevier Inc.)