Corneal biomechanical properties after SMILE versus FLEX, LASIK, LASEK, or PRK: a systematic review and meta-analysis

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Abstract
The aim of this study was to compare the postoperative corneal biomechanical properties between small incision lenticule extraction (SMILE) and other corneal refractive surgeries. A systematic review and meta-analysis were conducted. Articles from January 2005, to April 2019, were identified searching PubMed, EMBASE, Web of Science, and International Clinical Trials Registry Platform. Studies that compared SMILE with other corneal refractive surgeries on adult myopia patients and evaluated corneal biomechanics were included. Multiple effect sizes in each study were combined. Random-effects model was conducted in the meta-analysis. Twenty-two studies were included: 5 randomized controlled trials (RCTs), 9 prospective and 6 retrospective cohort studies, and 2 cross-sectional studies. Using the combined effect of corneal hysteresis (CH) and corneal resistance factor (CRF), which were obtained from ocular response analyzer (ORA), the pooled Hedges’ g of SMILE versus femtosecond laser-assisted in situ keratomileusis (FS-LASIK) was 0.41 (95% CI, 0.00 to 0.81; p = 0.049; I2 = 78%), versus LASIK was 1.31 (95% CI, 0.54 to 2.08; p < 0.001; I2 = 77%), versus femtosecond lenticule extraction (FLEX) was − 0.01 (95% CI, − 0.31 to 0.30; p = 0.972; I2 = 20%), and versus the group of photorefractive keratectomy (PRK) and laser-assisted sub-epithelial keratectomy (LASEK) was − 0.26 (95% CI, − 0.67 to 0.16; p = 0.230; I2 = 54%). The summary score of Corvis ST (CST) after SMILE was comparable to FS-LASIK/LASIK with the pooled Hedges’ g = − 0.05 (95% CI, − 0.24 to 0.14; p = 0.612, I2 = 55%). In terms of preserving corneal biomechanical strength after surgeries, SMILE was superior to either FS-LASIK or LASIK, while comparable to FLEX or PRK/LASEK group based on the results from ORA. More studies are needed to apply CST on evaluating corneal biomechanics after refractive surgeries.

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