Comparison of clinical outcome between femtosecond laser-assisted LASIK and SMILE for myopic astigmatism by vector analysis

Objective

To compare the accuracy and stability between corneal topography-guided femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) for myopic astigmatism by vector analysis.

Methods

A non-randomized controlled clinical trial was performed.One hundred and twenty patients (214 eyes) with myopic astigmatism who underwent the FS-LASIK or SMILE in Henan Eye Hospital from January 2020 to July 2020 were enrolled.The patients were divided into FS-LASIK group (58 cases, 105 eyes) and SMILE group (62 cases, 109 eyes) according to different surgeries.The visual acuity, refraction, intraocular pressure and corneal topography were examined before and 1 week, 1 month and 3 months after operation.The results of vector analysis between the two groups were compared, including target induced astigmatism vector (TIA), surgically induced astigmatism vector (SIA), magnitude of error (ME), angle of error (|AE|), difference vector (|DV|), correction index (CI), and index of success (IOS) 3 months after operation.This study protocol adhered to the Declaration of Helsinki and was approved by an Ethics Committee of Henan Eye Hospital (No.HNEECKY-2020[25]). Written informed consent was obtained from each patient before operation.

Results

Three months after surgery, no astigmatism was found in 11 eyes (10.5%), and with the rule (WTR) astigmatism was in 23 eyes (21.9%), and against the rule (ATR) and oblique astigmatism were in 71 eyes (67.6%) in FS-LASIK group.In SMILE group, no astigmatism was detected in 35 eyes (32.1%), and WTR astigmatism was in 58 eyes (53.2%), and ATR and oblique astigmatism were in 16 eyes (14.7%), showing a statistically significant difference between them (χ² =48.20, P<0.05). The postoperative SIA, |AE|, |DV|, CI and IOS values in the SMILE group were lower than those in the FS-LASIK group, showing statistically significant differences between them (all at P<0.05). The ME was -0.20 (-0.37, 0.00)D in FS-LASIK group and 0.20 (0.00, 0.25)D in SMILE group.Within 3 months after operation, there was no significant difference in ME among different time points in the FS-LASIK group (all at P>0.05) and in spherical equivalent (SE) among different time points in the SMILE group (all at P>0.05). There was significant difference in the results of vector analysis among different time points in the two groups (all at P<0.05).

Conclusions

Both FS-LASIK and SMILE are effective in the correction of myopic astigmatism.Astigmatism is slightly overcorrected by FS-LASIK and slightly undercorrected by SMILE.The axial error is smaller and the SE is more stable after SMILE within 3 months postoperatively.

Myopia; Astigmatism; Vector analysis; Lasers, excimer; Femtosecond laser