LASIK术后角膜后表面形态变化的研究

The changes of posterior surface elevation of corneal after LASIK

目的研究准分子激光原位角膜磨镶术(LASIK)术后角膜后表面的形态变化,探讨手术后应保留角膜的安全厚度。方法对135例(269眼)近视使用Orbscan裂隙扫描角膜地形图/角膜测厚系统,观察LASIK术后角膜后表面Diff值的变化。结果术后根据保留角膜厚度的不同分为3组,第1组保留角膜厚度>450μm,Diff值为(0.041±0.008)mm,第2组保留角膜厚度为410～450μm,Diff值为(0.057±0.013)mm,第3组保留角膜厚度为<410μm,Diff值为(0.080±0.014)mm。3组间比较均差异非常显著。术后保留角膜床厚度>280μm者,角膜后表面前凸值为(0.016±0.005)mm,保留角膜床厚度<280μm,前凸值为(0.034±0.009)mm,角膜后表面前凸值平均为(0.017±0.006)mm。结论 LASIK术后角膜后表面中央部均有不同程度的前凸。保留角膜床厚度和角膜后表面前凸值呈负相关。LASIK后角膜厚度至少应在410μm,残留角膜床厚度安全值应为280μm。

Objective To investigate the changes of corneal posterior surface after laser in situ keratomileusis （LASIK） for myopia,and identify the safe residual corneal thickness. Methods 269 eyes of 135 patients with myopia were measured with scanning slit corneal topography （Orbscan,Orbted,Inc.） preoperatively and postoperatively to observe the parameters of posterior surface difference of these groups. Results According to the different residual corneal thickness after surgery,we divided them into these groups. The residual corneal thickness of three groups were respectivelly greater than 450 μm,410-450 μm, 410 μm. And the parameters of posterior surface elevation difference of three groups were respectively （0. 041 ± 0. 008） mm,（0. 057 ± 0. 013） mm, （0. 080 ± 0. 014） mm. There was a significant difference among three groups. When the residual corneal thickness after surgery was greater than 280 μm,the posterior surface elevation of corneal was （0. 016 ± 0. 005） mm. When the residual corneal thickness after surgery was less than 280 μm,the posterior surface elevation of corneal was （0. 034 ± 0. 009） mm. The average of the posterior surface elevation of corneal was （0. 017 ± 0. 006） mm. Conclusion After LASIK,the midsection of the posterior surface of corneal has more or less anterior protrusion. The anterior protrusion of the posterior surface of corneal was opposite related to the thickness of the residual corneal bed. the thickness of corneal should be no less than 410 μm,the safe threshold value of residual corneal thickness was 280 μm.