Abstract：
OBJECTIVE: The aim of this study was to determine risk factors affecting changes in posterior corneal elevation (PCE) and predict the 5-year stability after small incision lenticule extraction (SMILE).
METHODS: This retrospective, longitudinal study enrolled 161 patients post-SMILE. The PCE values were measured at the apex, thinnest, maximal and 24 other prespecified preoperative points and at 6 months, 1 year and 5 years postoperatively.
RESULTS: Posterior corneas exhibited time-dependent, region-dependent and angle-dependent changes. For every dioptre increase in the absolute preoperative spherical equivalent (SE), 10-μm decrease in the central corneal thickness (CCT), 10-μm increase in the maximum lenticule thickness (MLT), 10-μm decrease in the residual bed thickness (RBT), 10% increase in the percentage ablation depth (PAD, MLT divided by CCT) and 10% decrease in the percentage stromal bed thickness (PSBT, RBT divided by CCT), PCE exhibited average forward displacements of 0.2-0.4, 0.2-0.7, 0.1-0.2, 0.1-0.3, 0.6-1.0 and 0.5-1.1 μm, respectively (p < 0.05). PSBT was the variable with the highest accuracy in predicting 5-year stability of posterior corneas (area under curve = 0.75). The cut-off values of SE, CCT, MLT, RBT, PAD and PSBT for increased PCE were -8.00 to -8.31 D, 481.0-498.5 μm, 139.5-144.5 μm, 255.5-263.5 μm, 26.9-28.3% and 48.9-52.6%, respectively.
CONCLUSIONS: Eyes with thinner corneas, higher myopia requiring greater MLT and lower RBT exhibited greater predispositions towards posterior protrusion. The thresholds for preventing forward posterior corneal displacement were 26.9-28.3% for PAD and 48.9-52.6% for PSBT. Prediction of posterior corneal stability is useful for assessing surgical risks post-SMILE.
METHODS: This retrospective, longitudinal study enrolled 161 patients post-SMILE. The PCE values were measured at the apex, thinnest, maximal and 24 other prespecified preoperative points and at 6 months, 1 year and 5 years postoperatively.
RESULTS: Posterior corneas exhibited time-dependent, region-dependent and angle-dependent changes. For every dioptre increase in the absolute preoperative spherical equivalent (SE), 10-μm decrease in the central corneal thickness (CCT), 10-μm increase in the maximum lenticule thickness (MLT), 10-μm decrease in the residual bed thickness (RBT), 10% increase in the percentage ablation depth (PAD, MLT divided by CCT) and 10% decrease in the percentage stromal bed thickness (PSBT, RBT divided by CCT), PCE exhibited average forward displacements of 0.2-0.4, 0.2-0.7, 0.1-0.2, 0.1-0.3, 0.6-1.0 and 0.5-1.1 μm, respectively (p < 0.05). PSBT was the variable with the highest accuracy in predicting 5-year stability of posterior corneas (area under curve = 0.75). The cut-off values of SE, CCT, MLT, RBT, PAD and PSBT for increased PCE were -8.00 to -8.31 D, 481.0-498.5 μm, 139.5-144.5 μm, 255.5-263.5 μm, 26.9-28.3% and 48.9-52.6%, respectively.
CONCLUSIONS: Eyes with thinner corneas, higher myopia requiring greater MLT and lower RBT exhibited greater predispositions towards posterior protrusion. The thresholds for preventing forward posterior corneal displacement were 26.9-28.3% for PAD and 48.9-52.6% for PSBT. Prediction of posterior corneal stability is useful for assessing surgical risks post-SMILE.
摘要：
目的：本研究的目的是确定影响后角膜抬高（PCE）变化的危险因素，并预测小切口微透镜摘除（SMILE）后5年的稳定性。
方法：本回顾性研究，纵向研究纳入161名SMILE后患者。在顶点处测量PCE值，最薄,最大和24个其他预先指定的术前要点和6个月时，术后1年和5年。
结果：后角膜表现出时间依赖性，区域相关和角度相关的变化。术前绝对等效球面(SE)屈光度每增加一次,中央角膜厚度（CCT）减少10μm，最大微透镜厚度（MLT）增加10μm，残余床层厚度(RBT)减少10μm，消融深度百分比增加10%(PAD，MLT除以CCT)和基质床厚度百分比减少10%(PSBT，RBT除以CCT)，PCE表现出0.2-0.4、0.2-0.7、0.1-0.2、0.1-0.3、0.6-1.0和0.5-1.1μm的平均向前位移，分别为(p<0.05)。PSBT是预测后角膜5年稳定性的准确性最高的变量（曲线下面积=0.75）。SE的截止值，CCT,MLT,RBT,PCE增加的PAD和PSBT为-8.00至-8.31D，481.0-498.5μm,139.5-144.5μm,255.5-263.5μm,26.9-28.3%和48.9-52.6%，分别。
结论：角膜较薄的眼睛，需要更大MLT和更低RBT的更高近视表现出更大的后突出倾向。PAD和PSBT预防角膜前移的阈值分别为26.9-28.3％和48.9-52.6％。预测后角膜稳定性可用于评估SMILE术后的手术风险。
方法：本回顾性研究，纵向研究纳入161名SMILE后患者。在顶点处测量PCE值，最薄,最大和24个其他预先指定的术前要点和6个月时，术后1年和5年。
结果：后角膜表现出时间依赖性，区域相关和角度相关的变化。术前绝对等效球面(SE)屈光度每增加一次,中央角膜厚度（CCT）减少10μm，最大微透镜厚度（MLT）增加10μm，残余床层厚度(RBT)减少10μm，消融深度百分比增加10%(PAD，MLT除以CCT)和基质床厚度百分比减少10%(PSBT，RBT除以CCT)，PCE表现出0.2-0.4、0.2-0.7、0.1-0.2、0.1-0.3、0.6-1.0和0.5-1.1μm的平均向前位移，分别为(p<0.05)。PSBT是预测后角膜5年稳定性的准确性最高的变量（曲线下面积=0.75）。SE的截止值，CCT,MLT,RBT,PCE增加的PAD和PSBT为-8.00至-8.31D，481.0-498.5μm,139.5-144.5μm,255.5-263.5μm,26.9-28.3%和48.9-52.6%，分别。
结论：角膜较薄的眼睛，需要更大MLT和更低RBT的更高近视表现出更大的后突出倾向。PAD和PSBT预防角膜前移的阈值分别为26.9-28.3％和48.9-52.6％。预测后角膜稳定性可用于评估SMILE术后的手术风险。
