Influences of SMILE and FS-LASIK on Corneal Sub-basal Nerves: A Systematic Review and Network Meta-analysis

PURPOSE: To compare postoperative corneal sub-basal nerve density and number between small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). METHODS: A search was made in PubMed, EMBASE, and the Cochrane library for prospective comparative studies. The analysis was divided into two parts: network meta-analysis and traditional meta-analysis of the studies directly comparing two surgical groups. Stata 16 (Stata Corporation) and Rev Man 5.4 (Cochrane) software were used to analyze the data. RESULTS: Twelve studies (n = 775) were included. In the network meta-analysis, the SMILE group showed a significant increase compared with the FS-LASIK group in corneal nerve density at 1 month postoperatively (mean: 4.23; 95% CI: 0.06 to 8.39, P < .05), and in the number of corneal nerve trunks at 6 months postoperatively (mean: 13.25; 95% CI: 10.20 to 16.30, P < .05). In the traditional meta-analysis, the SMILE group showed significant improvement compared with the FS-LASIK group in corneal nerve density at 1 (weighted mean difference [WMD]:-2.05, 95% CI:-3.11 to 1.00, P < .05) and 3 (WMD:-0.90, 95% CI:-1.30 to-0.50, P < .05) months postoperatively, and in the number of corneal nerve trunks (WMD:-2.52, 95% CI:-4.91 to-0.14, P < .05) and corneal nerve branches (WMD:-2.80, 95% CI:-3.41 to 2.19, P < .05) at 1 month postoperatively. CONCLUSIONS: The corneal nerve injury in the FS-LASIK group was worse than that in the SMILE group. The corneal nerve recovery in the SMILE group was better at 3 months postoperatively. However, there was no significant difference in corneal nerve density and number between the two groups at 6 months postoperatively.