Clinical Study On The Factors Of Astigmatism After SMILE

Objective:To investigate the factors associated with astigmatism after small incision lenticule extraction(SMILE).Methods:Sixty-nine patients(69 eyes)who underwent SMILE at The Second Hospital of Jilin University from December 2021 to December 2022 were included in the study.3months after SMILE,eyes with an objective refraction cylinder≥0.75 D were included in the astigmatism group(19 eyes),and eyes with an objective refraction cylinder<0.75 D were included in the control group(50 eyes).The results of routine preoperative and postoperative examinations at 1 day,1 week,1 month and 3 months,including uncorrected distance visual acuity(UCVA),corrected distance visual acuity(CDVA),objective optometry,corneal topography,and subjective optometry.The effective optical zone(EOZ)decentration was calculated using Pentacam tangential curvature difference maps and the corneal higher order aberration was calculated using Zernike’s polynomial(six order,scanning diameter of 6 mm)at 3 months postoperatively.Two independent samples t-test,Mann-Whitney test and Fisher’s exact test were used to compare the correlation factors between the two groups,and statistically significant factors were selected for univariate and multivariate logistic regression analysis.Result:1.UCVA was better in the control group than in the astigmatism group at 3months postoperatively(P < 0.05).There was no significant difference in UCVA between the two groups at 1 day,1 week and 1 month postoperatively,but it was slightly lower in the astigmatism group.2.Preoperatively,at 1 day,1 week,1 month and 3 months postoperatively,the cylinder was higher in the astigmatism group than in the control group(P < 0.05).3.There was no significant difference between the astigmatism group and the control group in terms of preoperative higher-order aberration,postoperative higher-order aberration and the difference of postoperative-preoperative higher-order aberration.4.There was no significant difference in the amount of horizontal decentration of the EOZ and the amount of vertical decentration of the EOZ between the astigmatism group and the control group.In the astigmatism group,the total decentration amount of the EOZ was higher than that of the control group(P < 0.05).5.The horizontal kappa angle in the astigmatism group was greater than that in the control group(P < 0.05).However,the vertical Kappa angle and total Kappa angle were not significantly different between the two groups.6.The anterior surface astigmatism was greater in the astigmatism group than in the control group(P < 0.05).There was no significant difference between the two groups for flat axial curvature,steep axial curvature,and axial of anterior surface astigmatism.7.Ocular residual astigmatism(ORA)was greater in the astigmatism group than in the control group(P < 0.05),and there was no significant difference between the two groups in the axial of ORA.8.Multivariate logistic regression analysis showed that preoperative cylinder and ORA were associated with the occurrence of postoperative astigmatism(P < 0.05).Conclusion:1.UCVA in normal eye superior to postoperative astigmatic eye at 3 months after SMILE.2.The postoperative cylinder remained stable after 1 week of SMILE,and there was no significant difference in higher order aberrations between the astigmatism and control groups at 3 months.3.The preoperative cylinder was higher in the astigmatism group,total decentration amount,horizontal kappa angle,anterior surface astigmatism and ORA were all greater in the astigmatism group than in the control group.4.Higher astigmatism and high ORA were independent risk factors for astigmatism after SMILE.