| Part ⅠComparison of dry eye and corneal sensitivity between small incision lenticule extraction and femtosecond LASIK for myopiaPurpose:To investigate the changes in dry eye symptoms and clinical signs and corneal sensitivity after small incision lenticule extraction (SMILE) and femtosecond LASIK (femto-LASIK).Design:Prospective, non-randomized comparative study.Methods:The study included a total of 71 eyes of 71 patients; the SMILE group comprised 38 eyes of 38 patients, and the femto-LASIK group comprised 33 eyes of 33 patients. Ocular Surface Disease Index (OSDI), Tear film breakup time (TBUT), the Schirmer test without anesthesia (S1T), corneal fluorescein staining, and central corneal sensation were evaluated before surgery and at 1 week,1 month 3 months, and 6 months after surgery.Results:OSDI scores in both groups were increased immediately and returned to preoperative level at 1 month after surgeries. The TBUT values in both groups were reduced after surgeries relative to their preoperative scores. Patients in SMILE group were less likely to have corneal staining compared with those in the femto-LASIK group ([odds ratio] OR= 0.5047,95%[confidence interval] CI:0.2753 to 0.9251, P= 0.0270). All tested areas within the cap or flap demonstrated corneal hypoesthesia immediately after both surgeries. SMILE-treated eyes showed less compromised corneal sensation than femto-LASIK-treated eyes at all postoperative visits in the central, inferior, nasal, and temporal areas at the 1-week and 1-month visits. In the SMILE group, the inferior, nasal, and temporal quadrants recovered faster than other areas. In the femto-LASIK group, the sensation over the entire flap did not recover to preoperative levels by postoperative 6 months. There was no correlation between postoperative corneal sensation and preoperative spherical equivalent, and ablation depth in both groups.Conclusions:SMILE surgeries resulted in short-term increase in dry eye symptoms, tear film instability, and loss of corneal sensitivity. Furthermore, SMILE surgeries have superiority over femto-LASIK in lower risk of postoperative corneal staining and less reduction of corneal sensation.Part Ⅱ Confocal comparison of corneal reinnervation after small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK)Purpose:To evaluate corneal reinnervation, and the corresponding corneal sensitivity and keratocyte density after small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK).Methods:In this prospective, non-randomized observational study,18 patients (32 eyes) received SMILE surgery, and 22 patients (42 eyes) received FS-LASIK surgery to correct myopia. The corneal subbasal nerve density and microscopic morphological changes in corneal architecture were evaluated by confocal microscopy prior to surgery and at 1 week,1 month,3 months, and 6 months after surgery. A correlation analysis was performed between subbasal corneal nerve density and the corresponding keratocyte density and corneal sensitivity.Results:The decrease in subbasal nerve density was less severe in SMILE-treated eyes than in FS-LASIK-treated eyes at 1 week (P-0.0147),1 month (P=0.0243), and 3 months (P=0.0498), but no difference was detected at the 6-month visit (P= 0.5277). The subbasal nerve density correlated positively with central corneal sensitivity in both groups (r=0.416, P<0.0001, and r=0.2567, P=0.0038 for SMILE group and FS-LASIK group, respectively). The SMILE-treated eyes have lower risk of developing peripheral empty space with epithelial cells filling in (P= 0.0005).Conclusions:The decrease in subbasal nerve fiber density was less severe in the SMILE group than the FS-LASIK group in the first 3 months following the surgeries. The subbasal nerve density was correlated with central corneal sensitivity. |
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