Comparison Of Two Refractive Procedures In Patients With Myopia With Myopic Astigmatism (Fs-Lasik And Smile) With Regard To The Centration Of The Procedure And Its Effect On Postoperative Outcomes

The aim of our study was to compare two surgical methods for the treatment of myopia with myopic astigmatism, each based on a different treatment centration strategy. FS-LASIK procedure using Visumax 500 for flap creation and MEL 90 for excimer ablation (both Carl Zeiss Meditec AG) uses eye tracker and cyclotorsion compensation. In SMILE using Visumax 500 without direct eyetracking and cyclotorsion compensation, the treatment is manually centred on a corneal vertex, with an adjustment for the Kappa angle. We assessed the relation of the Kappa angle with treatment decentration, and we focused on the effect of decentration on postoperative outcomes, residual astigmatism, and aberrations. 

Surgeries were performed between 2022 and 2024 at Lexum Eye Clinics, Prague, Czech Republic. 

Our study consisted of two groups of patients. Group A included 111 right eyes of patients (70 women/41 men) after FS-LASIK, with a mean age of 32±8 years. Mean preoperative spherical equivalent (SE) was -3.16±1.77 D. Mean angle Kappa was 0.19±0.10 mm. Group B included 127 right eyes of patients (81 women/46 men) after SMILE, with a mean age of 30±7 years. Preoperative SE was -4.05±1.75 D. Mean angle Kappa was 0.17±0.09 mm. Mean follow-up was 3 months. Observed parameters were postoperative uncorrected (UDVA) and corrected (CDVA) distance visual acuity, refraction, astigmatism (vector analysis using Alpins method), decentration of the treatment (based on tangential difference maps in Pentacam, OCULUS), and aberrations (Pentacam, OCULUS).

Mean postoperative UDVA was 0±0.06 logMAR in Group A, and 0±0.02 logMAR in Group B (p=0.948). Mean SE was -0.02±0.15 D in Group A, and -0.02±0.08 D in Group B (p=0.955). Comparison of groups showed significantly lower postoperative RMS HOA, coma vertical, and spherical aberration in Group B compared to Group A, while coma horizontal was lower in Group A. Mean decentration was 0.29±0.15 mm (0.04 to 0.69 mm) in Group A and 0.24±0.12 mm (0.05 to 0.53 mm) in Group B (p=0.054). No significant correlation was found between decentration and preoperative angle Kappa (lower ≤0.2 mm vs. higher >0.2 mm), and postoperative UDVA and CDVA, refraction, vector analysis parameters, and aberrations in any group. 

Our study indicates that the centration of SMILE procedure on the corneal vertex, with appropriate adjustment for the Kappa angle and manual correction of cyclotorsion, enables the achievement of optimal postoperative outcomes. Treatment decentration was comparable in both FS-LASIK and SMILE, and even slightly lower in SMILE, although the difference was not statistically significant. Mean decentration was low in both procedures and did not have impact on postoperative visual acuity, refraction, residual astigmatism, and aberrations.