Comparison of corneal epithelial remodeling and corneal aberration changes after FS-LASIK and FS-LASIK Xtra

Objective

To investigate the status of corneal epithelial remodeling and changes in corneal aberration after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and FS-LASIK combined with corneal collagen cross-linking (FS-LASIK Xtra), and to analyze the relationship between corneal epithelial thickness (CET) and corneal aberration.

Methods

A cohort study was conducted.A total of 172 patients (172 eyes) who underwent FS-LASIK at Yinhai Eye Hospital of Chengdu University of Traditional Chinese Medicine were enrolled from June 2021 to February 2022.The 172 eyes were divided into FS-LASIK group (94 eyes) and FS-LASIK Xtra group (78 eyes) according to the surgical procedure, with a total follow-up of 6 months.The cornea was divided into a central 2-mm ring and a ring of 2-5 mm centered on the central cornea.CET at 9 regions in the central 0-5 mm area was measured by OCT before and at 1, 3 and 6 months after surgery, and the corneal higher-order aberration (HOA) was measured by the iTrace visual function analyzer.The main outcomes were the increase in CET (ΔCET), and corneal HOA at 6 months after surgery.The relationship between central corneal ΔCET and corneal aberration was analyzed.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of Yinhai Eye Hospital of Chengdu University of Traditional Chinese Medicine (No.2021yh-009). Written informed consent was obtained from each subject.

Results

At 1, 3 and 6 months after surgery, the central, superior, superior nasal, nasal, inferior nasal, inferior, inferior temporal, temporal and superior temporal ΔCET were significantly smaller in FS-LASIK Xtra group than in FS-LASIK group (all at P<0.05). In FS-LASIK Xtra group, 6-month postoperative central, superior, superior nasal, inferior and inferior temporal ΔCET were significantly larger than those at 1 month after surgery, and 3- and 6-month postoperative temporal ΔCET were significantly larger than that at 1 month after surgery, and 6-month postoperative superior temporal ΔCET was significantly larger than those at 1 and 3 months after surgery (all at P<0.05). In FS-LASIK group, 3- and 6-month postoperative central, superior, inferior and inferior temporal ΔCET were significantly larger than those at 1 month after surgery, and 6-month postoperative superior nasal ΔCET was significantly larger than that at 3 months after surgery, and 6-month postoperative nasal, inferior nasal, temporal, superior temporal ΔCET were significantly larger than those at 1 and 3 months after surgery (all at P<0.05). There was no significant difference in vertical trefoil, vertical and horizontal coma changes at different time points after surgery between both groups (vertical trefoil: χ²_group=4.27, P=0.118; χ²_time=0.01, P>0.05.vertical coma: χ²_group=5.74, P=0.057; χ²_time=0.08, P=0.957.horizontal coma: χ²_group=3.97, P=0.137; χ²_time=0.51, P=0.773). The tilted trefoil changes at 1, 3 and 6 months after surgery of FS-LASIK Xtra group were significantly larger than those of FS-LASIK group (all at P<0.05). The 6-month spherical aberration change in FS-LASIK Xtra group was significantly higher than that at 1 month after surgery, and the 6-month spherical aberration change in FS-LASIK group was significantly higher than that at 1 and 3 months after surgery (all at P<0.05). The 6-month total HOA change in FS-LASIK group was significantly lower than that at 1 and 3 months after surgery (all at P<0.05). In FS-LASIK group, central corneal ΔCET was weakly positively correlated with spherical aberration at 1 and 6 months after surgery (r_s=0.257, P=0.008; r_s=0.244, P=0.012), and was weakly positively correlated with total HOA (r_s=0.253, P=0.009; r_s=0.279, P=0.004).

Conclusions

The postoperative ΔCET after FS-LASIK Xtra is smaller than that after FS-LASIK, but the homogeneity of ΔCET in each region is similar between the two groups.The changes in corneal HOA after surgery are similar in both groups, and there is a certain association between the overall epithelial distribution and corneal aberration.

Myopia; Corneal surgery, laser; Corneal wavefront aberration; Femtosecond laser; Corneal collagen crosslinking; Optical coherence tomography; Corneal epithelial remodeling