Clinical Study On Corneal Biological Characteristics After Corneal Refractive Surgery

Objective:To study the changes of the corneal thickness and the changes of the anterior and posterior corneal surface after corneal refractive surgery,and provide the basis for the selection of corneal surgery.Methods:39 cases of patients(60 eyes)with myopia in our hospital were collected from January 2016 to January 2017.Corneal topography indices were evaluated using SIRIUS system.The keratoconus vertex of of front(Kvf),keratoconus vertex of back(Kvb),corneal thickness of apex cornea,and corneal thickness in 0°,90°,180°,270°away from apex cornea 1.5mm,3mm,3.5mm was assessed preoperatively and 1 and 3months after FS-LASIK or TPRK.Optical quality was assessed with a clinical double-pass system preoperatively and 1 and 3 months after FS-LASIK or TPRK.The retinal image quality parameters(MTF cutoff frequency)were calculated.Data obeyed the normal distribution were compared using paired t-test.Data disobeyed the normal distribution were compared using Wilcoxon signed rank test.Results:1.There was no significant difference in the ablation depth in cornea apex and in 0°,90°,180°,270°away from apex cornea 1.5mm,3mm pre-and postoperation in 1 and 3 months(P>0.05).There was also no significant difference in two groups(P>0.05).There was no significant difference in the cornea thickness in 0°,90°,180°,270°away from apex cornea 3.5mm pre-and postoperation in 1 and 3 months(P>0.05).2.In corneal apex,there was no significant difference between the actual corneal ablation depth and theoretical corneal ablation depth(P>0.05).3.There was a linear correlation between corneal ablation depth in 0°,90°,180°,270°away from apex cornea 1.5mm and correction of diopter in FS-LASIK.With the pearson correlation analysis,the correlation coefficient r between corneal ablation depth in 0°,90°,180°,270°away from apex cornea 1.5mm and correction of diopter in TPRK were-0.357?-0.339?-0.409**?-409**(**P<0.05).4.With the pearson correlation analysis,the correlation coefficient r between corneal ablation depth in 0°,90°,180°,270°away from apex cornea 3 mm and correction of diopter in FS-LASIK were-0.193?-0.539**?-0.275?-0.196(**P<0.05),and in TPRK were-0.431**?-0.101?-0.332,-0.478**(**P<0.05).5.The Kvf was increased significantly in 1 and 3 months after operation than preoperative in two groups(P < 0.05).The Kvb was increased in 1 and 3 months after operation than preoperative in two groups without statistical significance(P>0.05).6.With the pearson correlation analysis,the correlation coefficient r between Kvf and corneal apex curvature,corneal apex thickness,correction of diopter,theoretical corneal ablation depth,residual bed thickness in FS-LASIK were-0.098,-0.170,-0.677**,0.677**,-0.550**(**P<0.05),and in TPRK were 0.201?-0.364?-0.333?0.333?-0.418**(**P<0.05).7.With the pearson correlation analysis,the correlation coefficient r between Kvf and corneal apex curvature,corneal apex thickness,correction of diopter,theoretical corneal ablation depth,residual bed thickness in FS-LASIK were-0.037,0.111,-0.067,0.067,0.020(P>0.05),and in TPRK were 0.251,-0.388,-0.002,0.002,-0.278(P>0.05).8.The MTF cut off decreased significantly 1 and 3 months after operation than preoperative(P<0.05).But there is no significant difference in two groups(P>0.05).The MTF cut off?30c/deg in two groups after operation.Conclusion:1.The effect of the corneal ablation depth from the cornea apex to peripheral cornea was gradually weakened in the whole optical treatment area.2.The changes of Kvf was related to correction of diopter,theoretical corneal ablation depth,residual bed thickness in FS-LASIK and TPRK pre-and postoperation.3.There was no statistical significance in the changes of Kvb in FS-LASIK and TPRK pre-and postoperation.