Comparison of Dry Eye Parameters and Corneal Sensation after FS-LASIK and SMILE Surgery

Objective: To compare the changes in dry eye parameters and corneal sensation between FS-LASIK (femtosecond laser-assisted in situ keratomileusis) and SMILE (small incision lenticule extraction), and to investigate the effect of the type of surgery on tear film and corneal sensation; to analyze the correlation between the two indicators. Methods: In this prospective non-randomized control study, 48 eyes of 24 patients underwent FS-LASIK and 41 eyes of 21 patients underwent SMILE. The tear meniscus height (TMH) and non-invasive tear film break-up time, including NIF-BUT and NIAvg-BUT, were measured by a Keratograph 5M ocular surface analyzer and were evaluated preoperatively and at 1 and 3 months postoperatively. Central corneal sensation was examined as well. Repeated measures ANOVA was used for preoperative and postoperative comparison within the same group; an independent sample t test was used for comparison of general data and dry eye parameters between the different groups; Spearman correlation analysis was used for the correlation between central corneal sensation and dry eye parameters. Results: The values of all dry eye parameters and central corneal sensation showed no differences before surgery between the two groups. In the FS-LASIK and SMILE groups, the TMH results decreased at both postoperative time points (F=21.213, P<0.001; F=14.648, P<0.001). The TMH results were higher in the SMILE group than that in the FS-LASIK group at both postoperative time points (t=-5.549, P<0.001; t=-3.028, P=0.003). In the FS-LASIK group, the NIF-BUT values decreased within 1 month after surgery (F=4.603, P=0.019). In the SMILE group, the NIF-BUT values presented no significant decrease at both postoperative time points (F=0.599, P=0.516). The NIF-BUT values were higher in the SMILE group than in the FS-LASIK group at 1 month postoperatively (t=-3.430, P=0.001). The NIAvg-BUT values in the FS-LASIK group decreased within 1 month after surgery (F=3.580, P=0.042). The NIAvg-BUT values presented no significant decrease at both postoperative time points in the SMILE group (F=0.274, P=0.761). The NIAvg-BUT values were higher at both postoperative time points in the SMILE group than in the FS-LASIK group (t=-2.395, P=0.019; t=-2.431, P=0.017). The central corneal sensation results had decreased at both postoperative time points in the FS-LASIK group (F=121.919, P<0.001), but had decreased at only 1 month after surgery in the SMILE group (F=54.032, P<0.001). The central corneal sensation results were better in the SMILE group than in the FS-LASIK group at both postoperative time points (t=-5.367, P<0.001; t=-3.242, P=0.002). There was a positive correlation between central corneal sensation and dry eye parameters at both follow-up time points in both groups (P<0.05). Conclusions: There are different degrees of change in dry eye parameters and central corneal sensation at the early postoperative period in the FS-LASIK and SMILE groups. The dry eye parameters and central corneal sensation in the SMILE group are better than those in the FS-LASIK group. There is a positive correlation between central corneal sensation and dry eye parameters in both groups. Key words: femtosecond assisted laser in situ keratomileusis; small insicion lenticule extraction; dry eye parameters; corneal sensation; keratograph 5M ocular surface analyzer