SMILE手术前后角膜形态学和生物力学特性变化的研究

目的探讨飞秒激光小切口角膜基质透镜取出术(SMILE)术后不同时间角膜形态欠规则但尚不能诊断圆锥角膜的患眼与角膜形态正常眼的生物力学变化特点,评估综合角膜地形图检查结果与角膜生物力学参数进行诊断对于筛查角膜屈光手术前的早期圆锥角膜的意义。方法选取2018年1至5月在北京同仁医院屈光中心接受SMILE手术者57例(104只眼)其中男性27例,女性30例,年龄(29.2±4.7)岁。根据Tomey角膜地形图中圆锥角膜严重程度指数(KSI)分为正常组(KSI<15%)35例(65只眼)与欠规则组(KSI≥15%)22例(39只眼)。收集患者的年龄、等效球镜度数、术前最佳矫正视力(BCVA)、术后裸眼视力。使用Pentacam三维眼前节分析系统测量的角膜最薄点中心3 mm区域前后表面曲率半径(ARC和PRC)、角膜最薄点厚度(THP)、角膜扩张综合偏差分析指数(BADD)。使用Corvis ST生物力学分析仪测量角膜生物力学参数(CBI)、角膜中央厚度(CCT)、非接触生物力学校正眼压(bIOP)、最大形变幅度(DA)、最大反向半径(M)、顶点和1 mm间形变幅度比值(DR)、硬度参数(SPA1)。运用Pentacam与Corvis ST联合诊断系统分析得出断层扫描生物力学指数(TBI)。对两组患者术前及术后1周、1个月、3个月、1年各参数及各组1周、1个月、3个月、1年与术前的DA、M、DR、SPA1差值(Δ)进行两组间比较。均采用独立样本t检验进行统计学分析。结果术前两组间年龄(t=0.20)、CCT(t=1.64)、DA(t=-1.85)、BIOP(t=0.73)、M(t=-0.24)、DR(t=-1.00)、屈光度SE(t=-0.97)与BCVA(t=0.21)差异均无统计学意义(P>0.05)。欠规则组TBI为0.28±0.20、CBI为0.09±0.21、BADD为1.33±0.47,明显高于正常组(t=-2.17,-6.78,-4.37;P<0.05),SPA1明显低于正常组(t=2.58,P=0.011)。正常组TBI为0.05±0.08、CBI为0.01±0.03、BADD为0.92±0.46;术后1周、1个月、3个月、1年两组裸眼视力(t=-0.31,0.36,0.24,0.63)、屈光度数(t=0.00,-0.22,0.90,0.73)及M(t=-1.80,-1.90,-0.78,-1.70)差异均无统计学意义(P>0.05)。欠规则组DA术后1和3个月均高于正常组(t=-3.13,-3.09;P<0.01),DR术后1周、1个月、1年均高于正常组(t=-2.72,-3.39,-2.51;P<0.05),SPA1术后1周、1个月、3个月均低于正常组(t=2.11,2.73,3.70;P<0.05)。术后1个月ΔDR欠规则组高于正常组(t=-3.01,P=0.003);术后1周、3个月、1年ΔDR差异均无统计学意义(t=-1.61,-1.40,-0.61;P>0.05);术后1周、1个月、3个月、1年两组ΔDA(t=0.50,-1.10,-0.73,2.12)、ΔM(t=-1.52,-1.41,0.01,-0.79)、ΔSPA1(t=0.89,0.90,1.12,0.90)组间比较,差异均无统计学意义(P>0.05)。结论角膜地形图形态欠规则眼与角膜形态正常眼在SMILE术后1年内角膜生物力学的变化均稳定且无明显差异。综合角膜地形图检查结果与角膜生物力学参数进行分析,对于角膜屈光手术前筛查早期圆锥角膜具有一定的意义。

Assessment of corneal biomechanical changes after small incision lenticule extraction with Pentacam and Corvis ST

Objective To investigate the application value of Pentacam combined with Corvis ST in evaluation of the changes of corneal biomechanics after femtosecond laser small incision lenticule extraction(SMILE)in Chinese myopia with an irregular cornea.Methods The clinical records for 104 eyes of 57 patients who received SMILE in the Refractive Center of Beijing Tongren Hospital during January 2018 and May 2018 were collected.According to the keratoconus severity index(KSI),they were divided into two groups:regular corneal group(KSI<15%)and irregular corneal group(KSI:15%to 25%).In both groups,the anterior corneal surface radius curvature was>7.25 mm(K<46.50 diopters),the posterior corneal surface radius curvature was>5.90 mm,the thinnest pachymetry was>490μm,and best corrected visual acuity was≥1.0.The vision,refraction,and corneal biomechanics before and after SMILE were assessed.The Topographic and Biomechanics Index(TBI)was analyzed by Pentacam combined with Corvis ST.Results Before SMILE,the Corvis Biomechanical Index(CBI),TBI,and Belin/Ambrósio Deviation Normalized Index(BADD)of the irregular corneal group were significantly higher(t=-2.17,-6.78,-4.37,P<0.05)than the regular corneal group,while the stiffness parameter(SPA1)was significantly lower(t=2.58,P=0.011)compared to the regular corneal group(P<0.05).In the irregular group,the TBI was(0.28±0.2);the maximum value was 0.03,and the minimum value was 0.43.The CBI was(0.09±0.21);the maximum value was 0.00,and the minimum value was 0.54.The BADD was(1.33±0.47);the maximum value was 0.42,and the minimum value was 2.26.In the regular group,the TBI was(0.05±0.08);the maximum value was 0.00,and the minimum value was 0.20.The CBI was(0.01±0.03);the maximum value was 0.00,and the minimum value was 0.17.The BADD was(0.92±0.46);the maximum value was 0.00,and the minimum value was 1.64.There was no significant difference between two groups in age(t=0.20,P=0.508),central corneal thickness(t=1.64,P=0.104),biomechanical corrected IOP(t=0.73,P=0.468),max inverse radius(t=-0.24,P=0.815),spherical equivalent(t=-0.97,P=0.335),and best corrected visual acuity(t=0.21,P=0.833).After SMILE,the deformation amplitude in the irregular group was significantly higher at 1 month and 3 months(t=-3.13,-3.09,P<0.05).The irregular group had a significantly higher deformation amplitude ratio at 1 week,1 month,and 1 year(t=-2.72,-3.39,-2.51,P<0.05).The SPA1 in the irregular group was significantly lower than the regular group at 1 week,1 month,and 3 months(t=2.11,2.73,3.70,P=0.335,0.010,<0.001).The changes of deformation amplitude(t=0.50,-1.10,-0.73,2.12,P>0.05),max inverse radius(t=-1.52,-1.41,0.01,-0.79,P>0.05),and SPA1(t=0.89,0.90,1.12,0.90,P>0.05)after SMILE were similar between the irregular and regular groups,except that at 1 month after SIMILE,the deformation amplitude ratio changed more significantly in the irregular group(t=-3.01,P=0.003).Conclusions The changes of corneal biomechanics in the groups of regular cornea and irregular cornea were stable with no significant difference during 1 year of post-SMILE.The diagnosis based on the corneal topography and corneal biomechanics is of certain significance for the screening of early keratoconus before keratorefractive surgery.