影响准分子激光原位角膜磨镶术前后球差变化的诸因素分析

Causes of increased spherical aberration induced by laser in situ keratomileusis

目的探讨准分子激光原位角膜磨镶术(laserinsitu keratomileusis,LASIK)的切削深度、治疗光区直径和术后角膜后表面前凸对术后球差变化的影响。方法随机选取采用波前像差引导的LASIK治疗的近视患者94例(185眼),患者屈光系统四阶球差值采用Zywave像差仪测量,术后第6个月患者球差值与术前值相减所得即为球差变化值(用ΔSA表示)。角膜后表面的前凸值采用Orbscan-IIz裂隙光扫描地形图测量,记录术中治疗光区直径和切削深度。采用多元逐级回归方法分析手术中切削深度、治疗光区直径和术后角膜后表面前凸与术后球差变化的相关性。结果术前四阶球差值为(-0.08±0.16)μm,手术切削量均值为(96.11±24.63)μm,治疗光区直径为(6.39±0.25)mm。术后第6个月,四阶球差值为(-0.96±0.61)μm,ΔSA为(-0.89±0.62)μm,角膜后表面前凸值为(44.00±12.00)μm。经相关性分析,ΔSA变化与切削量(r=-0.50,P<0.01)和术后角膜后表面前凸(r=-0.49,P<0.01)呈负相关,与切削光区直径(r=0.31,P<0.01)呈正相关。结论LASIK治疗近视后,患者的四阶球差呈负性增大趋势,球差变化值与手术切削深度及术后角膜后表面前凸呈负相关,与切削区直径呈正相关。

Objective To evaluate the changes in 4th-order spherical aberrations after laser in situ keratomileusis （LASIK）; to compare the related changes to ablation, the optic zone and the forward shift of the posterior corneal surface. Methods This prospective study was comprised of 185 eyes of 94 patients treated with wavefront-guided LASIK who were available for evaluation 6 months postoperatively. The 4th-order spherical aberrations （4th-SA） were measured with a Hartmann-Shack aberrometer before the operation and 6 months after the operation. The anterioposterior changes in the posterior corneal surface were measured using scanning-slit corneal topography, preoperatively and 6 months postoperatively. Multiple regression analysis was used to assess the factors that affected the changes in spherical aberrations after LASIK. Results The 4th-order spherical aberrations increased from （-0.08±0.16）μm before the operation to （-0.96±0.61）μm at 6 months after the operation, a change of （-0.89±0.62）μm. There was a statistically significant increase after LASIK （P 〈0.01）. Mean ablation depth was （96.11±24.63）μm and the treated area of the optic zone was （6.39± 0.25）mm. Six months postoperatively, the posterior corneal surface displayed a mean forward shift of （44.00±12.00）μm. Both ablation depth （r=-0.50, P〈0.01） and protrusion of the posterior corneal surface （r=-0.49, P〈0.01） showed negative linear correlations with the changes in 4th-order spherical aberrations. There was a positive linear correlation between the treated area of the optic zone and changes in 4th-order spherical aberrations （r= 0.31, P〈0.01）. Conclusion LASIK induced significant changes in 4th-order spherical aberrations. Both ablation depth and protrusion of the posterior corneal surface showed negative linear correlations with the changes. There was a positive correlation between the treated area of the optic zone and changes in 4th-order spherical aberrations.