准分子激光原位角膜磨镶术术后角膜后表面前凸和屈光力的变化

Changes in corneal thickness and refraction after LASIK

目的研究准分子激光原位角膜磨镶术(laser insitu keratomileusis,LASIK)术后角膜后表面前凸和屈光力的变化及影响二者变化的相关因素。方法对接受LASIK手术并有术后6个月随访记录、近视屈光度(等效球镜)为(-6.50±2.75)D的52例患者(76眼),于术前及术后第1个月、第2个月和第6个月分别行Orbscan-Ⅱ裂隙光扫描角膜地形图检查,测量角膜后表面前凸值、角膜后表面屈光力,观察其变化。用多元逐级回归法分析术前角膜最薄点厚度,以及眼内压、切削量与术后角膜后表面前凸的相关性。结果术后第1个月角膜后表面前凸值为(38.81±17.87)μm,术后第2个月为(35.61±13.60)μm,术后第6个月为(36.45±14.34)μm;3.0 mm直径角膜后表面屈光力均值术后第1个月为(-6.85±0.23)D,术后第2个月为(-6.83±0.28)D,术后第6个月为(-6.81±0.25)D;5.0 mm直径角膜后表面屈光力均值术后第1个月为(-6.34±0.24)D,术后第2个月为(-6.38±0.21)D,术后第6个月为(-6.39±0.25)D,上述观察值与术前比较差异有显著性(P<0.01),但术后第1个月同术后第2个月、第6个月比较差异无显著性。角膜后表面前凸值与角膜后表面屈光力线性相关(r=0.6,P<0.01)。多元逐级回归分析与术后角膜后表面前凸的变化有关系的变量为切削量(非标准系数B=0.405,P<0.01),角膜最薄点厚度(非标准系数B=-0.109,P<0.01),术前眼内压未进入最后回归方程。结论LASIK术后角膜后表面形态有显著性改变,角膜后表面呈锥形前凸,随术后时间延长角膜后表面形态趋于稳定;角膜厚度越薄、切削量越大则术后的角膜前凸值就越大。

Objective To evaluate changes in corneal thickness and refraction after liner in sire keratomileusis （LASIK） for myopia, and the relevant faetors that influence the results. Methods Seventy-six eyes of 52 patients with myopia or myopic astigmatism with spherical equivalent （SEQ） refractive errors of - 2.75 to - 12,50 diopters（D）, [mean, （ - 6.71 ±2.35） D] were included in the. study. CArnages in refraction and changes in the thickness of the corneal apex were measured with scanning-slit corneal topography （Orbscan, Orbtek, Inc.） prcoperatively and 1,2, and 6 months pestoperatively. The mean forward thinning of the corneal apex and refraction before and after LASIK wexe compared and the changes were analyzed. Multiple regression analysis was used to assess the fsctors that affect the thinning of the corneal apex. Remits After surgery, the posterior corneal surface displayed a mean forward shift （different-diff） of （38.81 ± 17.87） μm, （35.61 ± 13.60） μm, and （36.45± 14.34）μm, after 1 month, 2 months and 6 months, respectively. The mean posterior corneal refraction （3.0 mm dia） was （ -6.57±0.22）D preoperatively, and decreased to （-6.85±0.23） D, （-6.83±0.28）D and （-6.81±0.25）D, respectively, after 1 month, 2 months and 6 months. Mean posterior corneal refraction （5.0 mm dia） was （-6.26 ± 0.23）D preoperatively, and deereased to （-6.34 ± 0.24）D, （ - 6.38 ± 0.21）D and （ - 6.39 ± 0.25）D, respectively. The preoperative versus postoperative measurements were significantly different, but measurements taken at 1 month, 2 months and 6 months postoperatively did not show statistically significant differences, There was a significant correlation between protrusion and refraction of the posterior corneal surface （ r = 0.6, P〈 0.01）. Variables that have an effect on the forward shift of the posterior corneal surface, in the order of the magnitude of the influence, are the amount of laser ablation （partial regression coefficient B = 0. 405, B 〈 0.01 ） and the thinnest corneas （ B = - 0. 109, P 〈 0.01） preoperatively. Preoperative intraocular pressure correction showed collinearity with the, amount of laser ablation and the thinnest corneas. Conclusion Laser in situ keratomileusis （LASIK） induced significant refractive changes in the posterior corneal surface and a forward shift of the cornea. Eyes with thinner comeas and higher myopia requiring greater laser ablation are more predisposed to an anterior shift of the cornea.