Efficacy, safety, predictability, aberrations and corneal biomechnical parameters after SMILE and FLEx: Meta-analysis

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

BACKGROUND

The aim of this study was to compare the postoperative corneal biomechanical properties between small incision lenticule extraction (SMILE) and other corneal refractive surgeries.

METHODS

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.

RESULTS

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%).

CONCLUSIONS

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.

Comparison of the Different Preservative Methods for Refractive Lenticules following SMILE

Purposes: To (i) evaluate various methods for preserving refractive lenticules (RLs) from myopic eyes following small-incision lenticule extraction (SMILE), in order to (ii) establish a sound, standard storage RL preservative for clinical uses. Methods: In this prospective study, we compared freshly excised post-SMILE RLs (control group) with post-SMILE RLs (experimental group). Experimental group RLs were preserved in one of several preservatives: glycerol, allochroic silicagel desiccant, or Optisol. Following preservation in one of these three media, samples were evaluated by light microscopy (LM), and transmission (TEM) and scanning (SEM) electron microscopy on days-1, -3, -7, and -14. Results: Changes in cellular morphology were observed at all time points. Compared with fresh control-group RLs, there were significant histological changes in RLs preserved in glycerol and allochroic silicagel, but not Optisol. Comparison of the three methods revealed Optisol to be the best, followed by allochroic silica gel desiccant, followed by glycerol. RLs preserved in Optisol maintained the highest degree of viability and integrity. And the RLs viability and collagen density decreased with prolongation of storage time all. Conclusions: Optisol is a midterm corneal storage medium, which can maintain post-SMILE corneal RLs for 14 days, is a feasible and effective method for tissue storage.