| Objectives: To study the changes of corneal stress-strain index(SSI)and other major corneal biomechanical parameters of Corvis-ST for SMILE and FS-LASIK surgery;Observing the correlation between SSI,other major biomechanical parameters and other general parameters like CCT,IOP,SE;Analyzing the relevant factors affecting the biomechanical changes after the surgery.The effects of different surgical methods on corneal biomechanics and the application value of SSI in corneal biomechanical evaluation were evaluated.Methods: From December 2021 to December 2022,a total of 114 patients who volunteered for corneal refractive surgery were collected.According to the surgical methods,they were divided into SMILE group and FS-LASIK group,including 74 patients in SMILE group and 40 patients in FS-LASIK group.There was no significant difference in baseline data between the two groups.Corvis-ST examination was performed before operation,1 month and 3 months after surgery to obtain corneal biomechanical parameters including SSI,A1 T,A1L,A1 V,A2T,A2 L,A2V,PD,DA,DA Ratio,HC Radius,HCT,IRA,ARTh and SP-A1.The contents of the analysis include the correlation between the biomechanical parameters and other general parameters like CCT,intraocular pressure,SE;the changes of main biomechanical parameters after surgery and differences in the effects of the two surgical modalities on postoperative biomechanics.The Percent tissue altered(PTA)was calculated using the formula that Corneal cutting amount/Central corneal thickness,and the data was divided into high cutting ratio group(PTA>0.18)and low cutting ratio group(PTA<0.18)according to PTA.The correlation between SSI changes and PTA and the related influencing factors of postoperative SSI variation were explored in the end.Results:1.Before surgery,SSI was significantly correlated with other major biomechanical parameters(P <0.05),not related to age and CCT,but related to intraocular pressure and SE(P <0.01).2.Within-group comparison showed that except HCT,other major biomechanical indexes including SSI after surgery were significantly different from those before surgery(P <0.01),which was manifested as the decline of corneal biomechanical stability after the suegery(P <0.01).But there was no significant difference of those indexes between 3 months after surgery and 1 month after surgery(P >0.05).3.In the intergroup comparison,there was no significant difference in SSI at three time points between the two groups(P >0.05).PD,DA,DA Ratio and IRA of SMILE group were lower than those of FS-LASIK group at 1 month and 3 months after surgery(P <0.05),while A2 L,A1T,HC Radius,ARTh and SP-A1 were higher(P<0.05).The changes of HC Radius,DA Ratio,IRA,ARTh,and SP-A1 after SMILE were significantly lower than those after FS-LASIK(P <0.05).4.In the both surgical methods There was no significant correlation between the changes of SSI and PTA,there was no significantly difference in the changes of SSI between the high and low ablation ratio groups(P >0.05).The change of SSI was mainly correlated with the change of HC Radius(P <0.05).Different from SSI,the changes of DA Ratio and IRA after operation were significantly correlated with PTA(P <0.05),The greater the PTA,the greater the change of DA Ratio and IRA.Conclusions:1.SSI is considered as a corneal hardness parameter independent of CCT and IOP.This study shows SSI is independent of CCT and age,but related to intraocular pressure and the severity of myopia.Compared with other biomechanical indexes,SSI has certain advantages in terms of reflecting corneal stiffness independently.2.SSI and other major biomechanical indexes decreased significantly after the keratorefractive surgery,and achieve a new biomechanical balance after surgery.3.SMILE is superior to FS-LASIK in maintaining corneal biomechanical stability,but there was no difference in the effects on SSI.4.In this study,the change of SSI was not affected by PTA,but mainly correlated with the change of HC Radius. |
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