准分子激光原位角膜磨镶术后角膜后表面高度研究

Changes of elevation of posterior corneal surface after laser in situ keratomileusis for myopia

目的观察准分子激光原位角膜磨镶术(LASIK)术后角膜后表面高度的改变,探讨角膜后表面膨隆与剩余角膜基质床厚度(RBT),以及与激光切削所占角膜厚度比例(AP/TCT)的关系。方法回顾分析LASIK157例(157眼),根据RBT分组:组1为79眼,RBT≥350μm;组2为52眼,300μm≤RBT<350μm;组3为26眼,250μm≤RBT<300μm。根据AP/TCT分组:组A为44眼,AP/TCT≤10%;组B为84眼,10%<AP/TCT≤20%;组C为29眼,AP/TCT>20%。术前、术后1周、术后1个月、术后3个月、术后6个月应用OrbscanII行角膜地形图检查,分析比较各组各个不同时间点的角膜后表面膨隆程度。结果角膜后表面高度各组术后1周、术后1个月、术后3个月、术后6个月与术前比较,差异均有统计学意义(P均<0.05);术后同一时间点,组1、组2、组3组间及组A、组B、组C组间角膜后表面高度差异值(PED)两两比较差异有统计学意义(P均<0.05)。术后6个月PED值与RBT呈线性负相关(r=-0.77,P=0.00);与AP/TCT呈线性正相关(r=0.90,P=0.00),且与AP/TCT相关性更好。结论 LASIK术后角膜后表面均有不同程度的膨隆,并与RBT和AP/TCT相关;RBT不应为LASIK术后评价角膜后表面膨隆风险的唯一指标,AP/TCT是重要补充指标。

Objective To assess the changes in the elevation of the posterior corneal surface after laser in situ keratomileusis （LASIK） for myopia, and to analyze the surgical factors related to the ectasia of the posterior corneal surface, including the residual bed thickness （RBT） and the ablation percentage per total corneal thickness （AP/TCT）. Methods Retrospective analyses were applied to analyze the data of 157 patients （ 157 right eyes） after LASIK. According to RBT, the patients were divided into 3 groups： Group 1, 79 eyes, RBT≥350 um;Group 2, 52 eyes, 300 um≤ RBT 〈 350 um; Group 3, 26 eyes,250 um ≤ RBT 〈 300 um. According to AP/TCT, the patients were divided into 3 groups： Group A, 44 eyes, AP/TCT≤10% ; Group B, 84 eyes,10% 〈 AP/TCT≤20% ; Group C, 29 eyes, AP/TCT 〉 20%. Corneal topographies were obtained with Orbscan II preoperatively and at 1 week, 1 month, 3 months, 6 months after LASIK. The posterior elevation difference （PED） was used as indicator for the changes of elevation of the posterior corneal surface. Results Compared with that preoperatively, FED of the posterior corneal surface at every time point postoperatively was significantly different （ P 〈 0.05 ）. There was significant difference in PED among Group 1, Group 2 and Group 3 or anaong Group A, Group B and Group C at the same time point postoperatively （ P 〈 0. 05 ）. Furthermore, PED was negatively correlated with RBT（ r = -0.77, P = 0.00）, and positively correlated with AP/TCT（ r = 0. 90, P = 0.00）. The forward shift of the posterior corneal surface was more relative with AP/TCT than with RBT. Conclusions LASIK could induce posterior corneal surface ectasia postoperatively, which was relative with RBT and AP/TCT. RBT shonld not be the only factor to estimate the safety of LASIK, AP/TCT should be considered.