SMILE术后角膜帽的观察研究——基于傅里叶频域光学相干断层扫描（FD-OCT）

目的　通过傅里叶频域光学相干断层扫描（FD-OCT）对VisuMax飞秒激光制作角膜帽的早期临床观察，评价帽厚度的精确性、重复性、均一性及规整性，并研究SMILE术后不同方向不同时间帽厚度变化及其角膜上皮等可能的影响因素。方法　回顾性研究。选取44例（87眼）拟行SMILE术的近视患者，采用FD-OCT测量术后1周、1个月角膜6 mm直径范围内水平和垂直子午线方向的角膜帽厚度。应用RVe软件工具在每个截面图上特定的7个点标定角膜帽的厚度。采用配对样本t检验分析术后帽厚度预期值与实际值差异及术后不同时间帽厚度差异，术后角膜帽厚度与术前参数等相关性采用Pearson线性相关分析。结果　精确性:术后实际角膜帽厚度均较理论值厚，差异均有统计学意义（均为P<0.05）；重复性:术后1周、1个月水平方向帽厚度标准差分别为2.64 μm、3.41 μm，术后1周、1个月垂直方向帽厚度标准差分别为3.36 μm、3.10 μm；均一性:术后1周水平方向各位点的帽厚度差异有统计学意义（t=3.246，P=0.004）、术后1个月水平方向各位点的帽厚度差异也有统计学意义（t=2.295，P=0.034）；术后1周、1个月垂直方向各位点帽厚度差异均无统计学意义（均为P>0.05）。术后不同时间帽厚度相关影响因素:中央角膜厚度（CCT）与术后1周、1个月角膜帽厚度均存在正相关性（r=0.438、0.360，P＜0.001、0.001），术前角膜中央区上皮厚度与术后1周、1个月角膜帽厚度均存在正相关性（r=0.323、0.296，P=0.002、0.005），且CCT对术后角膜帽厚度的影响较大。多元线性回归方程结果显示:术后1周角膜帽厚度=96.226+0.032×CCT+0.212×术前角膜中央区上皮厚度，术后1个月角膜帽厚度=97.022+0.029×CCT+0.219×术前角膜中央区上皮厚度。结论　飞秒激光制帽早期可有良好的可重复性，且角膜帽形态均一、规整。随着术前CCT及角膜中央区上皮厚度的增厚，术后帽厚度较预设帽厚度厚，影响制帽的精确性。其中术前角膜CCT是影响角膜帽厚度的主要因素。

Observation of corneal cap after SMILE by FD-OCT

Objective To conduce early clinical evaluation of corneal cap made by VisuMax femtosecond laser using fourier-domain optical coherence tomography(FD-OCT),evaluate the precision,repeatability,uniformity and regularity of corneal cap thickness and analyze changes of cap thickness at different directions and time points and other related influencing factors including corneal epithelium.Methods A retrospective study was conducted on 44 myopic patients(87 eyes)who were scheduled to received SMILE operation.The thickness of corneal cap was measured within 6 mm diameter at two meridians(horizontal direction and vertical direction)by FD-OCT 1 week and 1 month after operation.RVe software was used to detect thickness of corneal cap at specific 7 points in each sectional view.Paired sample t test were used to compare the difference between the expected and actual values of cap thickness and the difference of cap thickness at different postoperative times.Correlation between postoperative cap thickness and preoperative parameters was analyzed by Pearson linear correlation analysis.Results Accuracy:The actual postoperative corneal cap thickness was thicker than the theoretical value,and the differences were statistically significant(all P<0.05).Repeatability:At postoperative 1 week and 1 month,the standard deviations of corneal thickness were 2.64μm and 3.41μm in horizontal direction,3.36μm and 3.10μm in vertical direction.Uniformity:There were statistical differences in cap thickness among different sites in horizontal direction at postoperative 1 week and 1 month(t=3.246,P=0.004;t=2.295,P=0.034),but no difference was found in cap thickness among different sites in vertical direction at postoperative 1 week and 1 month(all P>0.05).Related factors of cap thickness at different postoperative times:Corneal cap thickness at postoperative 1 week and 1 month had positive correlation with central corneal thickness(CCT;r=0.438,P<0.001;r=0.360,P<0.001)and central corneal epithelium thickness(r=0.323,P=0.002;r=0.296,P=0.005).CCT had a greater effect on postoperative corneal cap thickness.Multiple linear regression equation indicated that:Corneal cap thickness at postoperative 1 week=96.222+0.032×CCT+0.212×preoperative central corneal epithelium thickness;corneal cap thickness at postoperative 1 month=97.022+0.029×CCT+0.219×preoperative central corneal epithelium thickness.Conclusion Corneal cap made by femtosecond laser has a good repeatability,and was with uniform and regular shape.With the thickening of preoperative central corneal epithelium thickness and CCT,the postoperative cap thickness is thicker than theoretical value,which affects the accuracy of cap.Preoperative CCT is the main factor affecting corneal cap thickness.