An early clinical study on femtosecond small incision lenticule extraction for myopia and myopic astigmatism with different target refraction designs

Objective To evaluate the predictability and efficacy of femtosecond small incision lenticule extraction (SMILE) with different refractive targets in order to provide data for the clinic.Methods This was retrospective clinical study that included 207 eyes from 104 patients who were treated for myopia or myopic astigmatism with SMILE surgery.The spherical equivalent (SE) of subjective manifest refraction less than-8.25 diopters (D) and astigmatism less than-3.25 D.SMILE surgery was performed on all eyes and patients were followed for 3 months.Patients were divided into three groups based on target refractions:group Ⅰ (target refraction was 0.00 D),group Ⅱ (target +0.25 D) and group Ⅲ (target +0.50 D).Preoperative mean SE refraction for group Ⅰ was-6.26±1.47 D,group Ⅱ was-5.62±1.43 D and group Ⅲ was-4.31±2.75 D.All surgeries were performed by the same doctor and uncorrected visual acuity (UCVA),refraction and residual astigmatism were measured 1 day,7 days,1 month and 3 months postoperatively.An analysis of variance was used to analyze the changes in visual acuity and refraction at the different time points.Results ①Differences in postoperative uncorrected visual acuity (UCVA) at the different time points were insignificant for the 3 groups (F=2.67,0.82,0.62,0.25,P＞0.05).②The differences in target refraction at 1 day,7 days,1 month and 3 months postoperatively were also insignificant for the three groups (F=1.88,1.03,2.18,P＞O.05).Conclusion Clinical outcomes of SE and UCVA were stable for different target refractions with the SMILE procedure for myopia and myopic astigmatism.This study suggests that the nomogram needs to be adjusted for different ages to account for potential refractive changes.Nomogram adjustment is safe and feasible for controlling overcorrections within 0.50 D. Key words: Femtosecond laser;  Small incision lenticule extraction;  Refractive target;  Myopia ;  Myopic astigmatism