Clinical Study On The Factors Of Refractive Regression After SMILE For High Myopia

Objective:To evaluate the factors affecting refractive regression after small incision lenticule extraction?SMILE?for High Myopia.Method:The study included 30 patients?54 eyes?with high myopia who underwent SMILE at the Second Hospital of Jilin University from December 2018 to December 2019.Patients with postoperative uncorrected visual acuity?UCVA?<1.0 and the spherical degrees<-0.5D after ciliary muscle paralysis were included in the regression group and those with UCVA?1.0 in the control group,the regression group included4 patients?6 eyes?and control group included 26 patients?48 eyes?.Preoperative routine examinations of all patients were recorded,including UCVA,computer optometry,non-contact intraocular pressure IOP_NCT,Pentacam preocular segment analysis system for measuring corneal central thickness?CCT?,corneal curvature,and correct intraocular pressure IOPshah.And all patients were re-examined at 1 week,1 month,3 months and 6 months after surgery.Effective optical zone?EOZ?diameter was calculated by using Pentacam tangential curvature differential map at postoperative 6 months in all patients.The diameters of six main meridian optical zone?0-180,30-210,60-240,90-270,120-300,150-330?were recorded respectively and then the average diameters of the actual optical zone were calculated after surgery.The relative factors affecting refractive regression were analyzed by comparing the above measurements of the two groups.Data were analyzed statistically using independent sample t test,paired sample t test,chi-square test,and pairwise comparison used least significant difference,and univariate logistic regression analysisResult:1.There was no significant difference in sex,age,preoperative spherical equivalent?SE?,non-contact intraocular pressure,corrected intraocular pressure,corneal curvature Km and CCT between the regression group and the control group.2.There was significant difference in SE between the regression group and the control group at 1 month,3 months and 6 months postoperatively?P<0.001?,but no significant difference at 1 week postoperatively.3.There was no significant difference in IOP_NCTCT and IOPshah between the two groups at 1 week,1 month,3 months and 6 months after surgery?P>0.05?.There was no significant difference in IOP_NCTCT and IOPshah between 1 week and 1 month,3 months and 6 months after surgery and there was significant difference between 1 month and 3months after surgery in the regression groups?P<0.05?;And there was no significant difference between 1 week and 1 month,1 month and 3months,3 months and 6 months after surgery in the control groups.4.There was no significant difference in Km between the two groups at 1 week,1 month,3 months and 6 months after surgery;there was significant difference between 1 month and 3 months,3 months and6 months after surgery,and there was no significant difference between 1week and 1 month in the regression group;there was significant difference between 1 month and 3 months after surgery,and there was no significant difference between 1 week and 1 month,3 months and 6months after surgery in the control group.5.The difference of Km before and after surgery?preoperative-postoperative 6 months?,pre and post-operative change rate?pre and post-operative difference/preoperative Km?,postoperative difference?postoperative 6 months-postoperative 1 week?and Km postoperative change rate?postoperative difference/postoperative 1 week?between the two groups were statistically significant.6.There was no significant difference in postoperative CCT and predicted cutting thickness,and the difference of actual cutting thickness,cutting error?predicted cutting-actual cutting CCT?,deviation rate of cutting thickness?cutting error/predicted cutting CCT?and cutting thickness ratio?actual cutting/preoperative CCT?were all statistically significant between the two groups.7.There were significant differences in meridian 0-180,30-210,120-300,150-330 EOZ diameter,mean and predicted optical zone,there was no significant difference in other meridian EOZ,the difference?predicted-mean optical zone?and the deviation rate?difference/predicted optical zone?between the regression group and the control group.Conclusion:1.There was no correlation between refractive regression and sex,age and CCT,IOP,Km,SE,UCVA,IOP fluctuation before and after surgery;2.The actual cutting thickness after surgery was less than the predicted cutting thickness,and the cutting error was positively correlated with the refractive regression,and the greater the error was,the greater the incidence of refractive regression was;3.Refractive regression was negatively correlated with the corneal Km difference before and after surgery.The smaller the difference was,the easier the regression was,and refractive regression due to corneal ectasia after surgery;4.The actual optical zone after surgery was smaller than the predicted optical zone,the refractive regression was negatively correlated with the actual optical zone,the larger the optical zone diameter was,the less likely the refractive regression was to occur,and the horizontal meridian was more correlated than the vertical meridian.