Early Changes In Posterior Corneal Elevation And Related Factors After LASIK With Femtosecond And SBK

Background Femtoseeond laser flap creation(FS-LASIK)has good salty and predictability in the treatment of refractive error,but few studies have examined the dynamic change of posterior corneal elevation after FS-LASIK.The change of posterior corneal elevation after FS-LASIK is of important significance for the prevention of iatrogenie corneal expand after the surgery.Objective This study was to compare the early change of posterior corneal elevation with Femtosecond laser assisted LASIK(FS-LASIK)and sub-Bowman keratomileusis(SBK)by Oculyzer and analyze the related factors after FS-LASIK.Methods 91 eyes of 46 patients with myopia or myopic astigmatism in our hospital from January to May in 2016 were divided into FS-LASIK group(53 eyes of 27patients),SBK group(38 eyes of 19 patients)and explored every part of corneal elevation change values after FS-LASIK and SBK surgeries.The posterior corneal elevation was measured twenty-seven measuring points along the four zones(vertex,and 1mm,2mm and 3mm radius which is center,paracentral,midperipheral,and periphery)using Oculyzer preoperatively,l day,7 days and 1 month postoperatively,respectively.The results were analyzed with repeated measures ANOVA and Multiple linear regression analysis by SPSS 16.0 software.Results In the FS-LASIK group,the posterior corneal elevation difference values in the center were(-0.924±1.859)μm、(-1.151±1.586)μm、(-0.940±1.994)μm 1 day,7 days and 1 month postoperatively,respectively.In the periphery,the elevation difference values were(1.046±1.667)μm、(1.172±1.566)μm、(1.023±1.622)μm with the follow-up visits.In the paracentral and midperipheral displayed slightly backward or forward shift of cornea.In the SBK group,the posterior corneal elevation difference values of the vertex were(-0.684±1.454)μm、(-1.053±1.723)μm、(-0.553±1.572)μm 1 day,7 days and 1 month after operation.In the paracentral and midperipheral displayed the same trend with FS-LASIK group,and in the periphery,the values were(1.207±1.317)μm、(1.327±1.529)μm and(1.208±1.415)μm at various time points.there were no statistically significant differences in posterior corneal elevation between the two surgery modes and three time points(P>0.05).At 1 month postoperatively,It was only two independent variables which were spherical equivalent(SE)and ablation depth(AD)that entered the regression in the center and paracentral,Independent variables Such as central thinnest corneal thickness(TCT),spherical equivalent(SE),ablation depth(AD),residual bed thickness(RBT)and the ratio of AD and TCT(AD/TCT)did not enter the regression in other two areas.Conclusions The posterior corneal elevation in the central 6mm area showed tiny change in the early stage and the variation is larger 7 days after operation.On the basis of reserve enough RBT,the posterior corneal elevation appeared tiny change,but with the increase of SE and AD,variation gradually increases.