Clinical Efficacy And Corneal Biomechanical Changes Of LASEK Combined With CXL In Correction Of Myopic And Myopic Astigmatic Eyes

Background:The safety 、effectiveness and stability of corneal refractive has been strongly corroborated by the development of corneal refractive over more than 40 years.For patients with occult keratoconus before operation or excessively excised corneal tissue during operation,corneal resistance may decrease and corneal dilatation may occur after operation.Corneal dilatation is one of the serious complications after corneal refractive surgery,which is characterized by progressive thinning of stroma and steepening of central or asymmetric cornea.Corneal morphological examination and biomechanical parameters evaluation before refractive surgery can detect patients with early keratoconus and avoid corneal dilatation after refractive surgery.There is no unified understanding of whether corneal refractive surgery can be performed in patients with irregular corneal morphology and poor biomechanical parameters before surgery,but do not meet the diagnostic criteria of early keratoconus.Evidence-based medicine is needed for such patients to correct ametropia,improve their vision and quality of life,and avoid corneal dilatation.Objective:To evaluate the safety,effectiveness and clinical effect of excimer laser subepithelial keratomileusis combined with corneal collagen cross-linking for myopia and myopic astigmatism with poor corneal morphology or biomechanical parameters found by examination before refractive surgery,and to compare the results with those of myopia and myopic astigmatism with LASEK surgery alone,and to explore the changes of corneal biomechanics before and after surgery in the two groups.Methods:Prospective non-randomized controlled study,including 50 patients(30 males and 20 females,aged18-38 years)with myopia and myopic astigmatism who underwent LASEK-CXL in Henan Provincial People’s Hospital from January 2021 to January 2022,and 58 patients(25 males and 33 females,aged18-34 years)who underwent simple LASEK surgery at the same time as the control group.The patients were followed up before operation,1 day,3 days,1 week,2 weeks,1 month,3 months,6 months and 12 months respectively.The parameters of the affected eyes were recorded at 2 weeks,1 month,3 months,6months and 12 months after operation,including Uncorrected Visual Acuity(UCVA)(Log MAR),Best Corrected Visual Acuity(BCVA)(Log MAR),The Mean Endothelium Cell Density(MCD),and The Mean Endothelium Cell Density,(MCD)were recorded in the affected eyes.Corneal topography Pentancam to measure corneal morphological parameters: steep axis corneal curvature(Ksteep),flat axis corneal curvature(Kflat),Thinnest Corneal Thickness(TCT),and Corvis ST to measure corneal biomechanical parameters: stiffness parameter applanation 1(SP-A1),deformation amplitude ratios between the apex and the 2mm position,(DA Ratio 2mm),deformation amplitude ratios between apex and 1mm(DA Ratio1mm),integrated radius(IR),horizontal Ambrosio-related thickness(ARTh),radius of inverse curvature(Radius),Max Inverse radius(MIR),Peak Distance(PD),biomechanical intraocular pressure(BIOP),biomechanical index(Corvis biomechanical index(CBI).Generalized estimating equations were used to statistically analyze the data.The preoperative baseline characteristics and postoperative diopter were compared by independent sample t-test,and the postoperative biomechanical parameters were statistically analyzed by generalized estimation equations.Generalized estimating equation(GEE)regression models with repeated measurements were used to analyze the indices of the two groups at different time points.In this study,the main effects of group and time and the interaction effects between group and time were investigated in the GEE using repeated measurements of the two groups at preoperative and 5 follow-up points and adjusting the corresponding baseline values,and multiple comparison statistical methods were performed.Result:There were no significant differences in the preoperative baseline data of the two groups except corneal thickness.The operation was successful in both groups,and the epithelium healed 3-5 days after operation,and the bandage scope was removed without complications.The UCVA in LASEK-CXL group was significantly improved,and the safety and efficacy of LASEK-CXL group in 1 year after surgery were(1.15±0.20,1.15±0.21)respectively,which were similar to those in LASEK alone,and the difference was not statistically significant.The relative baseline change values decreased significantly in the LASEK group compared with the LASEK-CXL group at 2 weeks,1 month,and 6 months after SP-A1,with differences between groups of(11.14(3.03 to 19.26),10.01(4.05 to 15.96),7.01(1.08 to 12.94),(9.11(0.44 to 17.79),p<0.05)respectively.The relative baseline change values in the LASEK group increased significantly compared to the LASEK-CXL group in 2 weeks,1,3and 6 months after DA Ratio 2mm surgery,with the difference between the groups being(-0.30(-0.54 to-0.05),-0.30(-0.50 to-0.11),-0.35(-0.53 to-0.18),-0.32(-0.55 to-0.10),p<0.05),and the relative baseline change values in the LASEK group decreased significantly compared with the LASEK-CXL group at 2 weeks,1,3,6,and 12 months after ARTh,with the difference between the groups being(47.89(1.21 to 94.57),34.16(6.03 to 62.29),58.30(33.44 to 83.16),43.96(16.29 to 71.62),44.02(11.90 to 76.13),p<0.05),respectively,and the relative baseline change values in the LASEK group at 1 and 3 months after BIOP(1.52(0.71 to 2.33),1.77(0.94 to 2.60),p<0.05),respectively,and the relative baseline change values in the LASEK group increased significantly compared to the LASEK-CXL group at 2 weeks,1,3,6,and 12 months after CBI,with the difference between the groups being(-0.21(-0.32 to-0.09),-0.19(-0.27 to-0.11),-0.24(-0.31 to-0.17),-0.17(-0.26 to-0.07),-0.17(-0.29 to-0.05),p<0.05)respectively.Conclusions:1.Both LASEK-CXL and LASEK surgery are safety and effectiveness in the correction of ametropia.2.The biomechanical strength of cornea decreased significantly after both methods,but the change of corneal biomechanical parameters after LASEK-CXL was significantly lower than that after LASEK.3.LASEK-CXL is safe and effective in correcting ametropia,has little effect on corneal biomechanics,and can prevent corneal dilatation after refractive surgery.The long-term effect needs further observation.