Study On Changes And Influencing Factors Of Effective Optical Zone After Smile Surgery

ObjectiveTo investigate the changes of the effective optical zone at different time after femtosecond laser small lenticule extraction(SMILE),and to analyze corneal curvature,sphericity degree,preoperative corneal Q values and so on which may affect the size of the effective optical zone.MethodsIn this retrospective study,49 patients(89 eyes)who had received SMILE surgery to correct myopia and astigmatism were selected.Their optical zone were 6.6mm.All patients were evaluated by the Pentacam system.The Wilcoxon test was used to compare the changes of the effective optical zone after surgery.According to the size of the effective optical zone the group was divided into the large optical zone group(≥5 mm)and the small optical zone group(4～5mm).Precorrection diopter,Km value and effective optical zone size after the operation were analyzed by Pearson correlation analysis.The parameters with linear correlation and the size of the effective optical zone are analyzed by linear regression.The preoperative and postoperative parameters were analyzed by independent sample T test and Mann-Whitney test.Results1.The size of the effective optical zone at 3 and 6 months after surgery was smaller than that of the preset optical zone(1.52±0.35)mm and(1.51±0.37)mm,with statistically significant differences(Z=0.201,P<0.001;Z=0.228,P<0.001).The size of the effective optical zone at 3 and 6 months were(5.08±0.35)mm and 5.09±0.37 mm which have significant differences.2.The size of the effective optical zone at 3 and 6 month after surgery was positively correlated with the equivalent sphericity and sphericity degree(r=0.483,0.532;R =0.467,0.508,both P <0.001).There was a negative correlation with the preoperative corneal Q value(r=-0.349,-0.309,both P< 0.001).Linear regression was conducted and the size of the effective optical zone at 3 months after surgery =5.265+0.117* SD-1.292 *Q value.Effective optical zone size at 6 months after surgery =5.308+0.119* SD-1.226 *Q.3.The equivalent sphericity,sphericity degree and preoperative corneal Q values of the large effective optical zone group(≥5mm)mm and the small optical zone group(4～5)mm showed statistically significant differences(T=6.057,5.429,-2.522,P<0.05)before surgery.No significant difference was observed between the large effective optical zone group and the small effective optical zone group in the equivalent sphericity refraction and sphericity refraction(P>0.05).The Q value in the different effective optical zone group was(0.40±0.26)and(0.80±0.25)respectively at 6 months after the operation,and the difference was statistically significant(P<0.05).4.The uncorrected visual acuity of the treated eyes at 3 month and 6 months after the operation reached 20/25.94%(84/89)of eyes with UCVA reached 20/20 or above,and 93%(83/89)of eyes with UCVA reached 20/16 or above at 3 month after the operation.99%(88/89)of patients had UCVA of 20/20 or above,and 93%(83/89)of patients had UCVA of 20/16 or above at 6 month after the operation.Conclusions1.SMILE operation for Myopia and myopic astigmatism was the safety,effectiveness and predictability2.The effective optical zone of SMILE is smaller than the preoperative optical zone,and the spherical diopter before operation may be the main factor affecting the diameter of the effective optical zone.3.The larger the effective optical zone(≥ 5mm)is,the better the effect of astigmatism correction.