Change of higher order aberration after 2 mm micro-incision SMILE in myopia

Background Small incision lenticule extraction (SMILE) is increasingly used for myopia.However,the size of the incision varied in different operators.The influence of 2 mm micro-incision SMILE on postoperative diopter and aberrations is not clear yet. Objective The aim of the current study was to perform a clinical analysis of the efficacy,safety,stability and predictability of 2 mm micro-incision SMILE and investigate the influence of preoperative sphere and cylinder power on postoperative aberrations. Methods A serial cases observational study was carried out under the approval of Ethic Committee of Tianjin Eye Hospital and informed consent of each patient.Fifty-five eyes of 31 subjects with myopia and myopic astigmatism were enrolled in this study in Tianjin Eye Hospital from January to April 2013 and a 2 mm micro-incision SMILE was performed on the eyes.Follow-up visits were performed at 1 week,1 month and 6 months after operation.Uncorrected visual acuity (UCVA),best corrected visual acuity (BCVA),manifest and cycloplegic refraction were examined at each postoperative time points to evaluate the efficacy,safety,stability and predictability of 2 mm micro-incision SMILE.Wave-front aberrations were measured by WaveScan aberrometer.Repeated measurement analysis of variance was used for the comparison of the differences of aberrations before and after the surgery.And the differences between various follow-up visits were compared with LSD-t test.The relationship between preoperative sphere or cylinder power and aberrations postoperatively were analyzed by Spearman rank correlation. Results At 1 week,1 month and 6 months postoperatively,the effective index was 1.2,and the safety indexes were 1.2,1.2 and 1.5 respectively.The spherical equivalent remained 0.00 D at each postoperative time point.And 96.4% and 97.8% of eyes were within ±0.5 D of intend correction and 100% were within ±1.0 D of the intend correction at 1 month and 6 months postoperatively.Vertical coma (Z7) and spherical aberration (Z12) were significantly raised at 1 week,1 month and 6 months after surgery compared with the values preoperatively (Z7:t=9.668,10.607,9.772,all at P 0.05).Third-order to sixth-order aberrations and higher order abberration (HOA) showed significant increase at various time points after the surgery compared with the values before surgery (all at P 0.05).Positive correlations were found between preoperative sphere and S3,S4 and HOA at 1 week,1 month and 6 months postoperatively (P<0.05).Negative correlations were found between preoperative cylinder and S3,S4 and HOA at postoperatively various time points (all at P<0.05).In addition,significant positive correlations were seen between Z7 and preoperative cylinder as well as between Z12 and sphere preoperatively,and negative correlations also were observed between Z7 and preoperative sphere as well as between Z12 and cylinder preoperatively at each follow-up visits(all at P<0.05). Conclusions SMILE with 2 mm micro-incision is a safe, effective, stable and predictable procedure for myopic and myopic astigmatism eyes. The aberrations and Zernike terms remain stable after surgery until 6 months although these parameters present elevation to a certain extent. Preoperative SE and astigmatism power affect postoperative aberrations. Key words: Adult; Aberrometry; Myopia/surgery; Refraction, ocular; Corneal wavefront aberration; Femtosecond laser; Microsurgery; Small incision lenticule extraction