近视散光患者角膜形态对高阶像差的影响

Influence of corneal topography on higher order aberrations in myopic astigmatic patients

目的探讨近视散光患者高阶像差的分布特点及角膜形态对其的影响。方法用wavescan wavefront system波前像差仪对LASIK术前281例(434眼)近视散光患者进行客观测量,用TMS-4角膜地形图仪获得角膜表面规则指数(surface regularity index,SRI)、角膜表面不对称指数(surface asymmetry index,SAI)以及角膜表面形态。对屈光度、SRI和SAI与高阶像差作相关分析,将患者分别按角膜形态分为5组,对各组间的高阶像差的均方根值(root mean square,RMS)作秩和检验。结果6.0mm瞳孔直径下的总高阶像差(root mean square of higher order aberrations,RMSh)的均方根值为(0.286±0.098)μm,从3阶至6阶大致呈递减趋势,其中以3阶彗差、三叶草和4阶球差的均数最大。屈光力和SRI与RMSh没有显著的相关性,SAI与RMSh呈正相关,Pearson相关系数为0.161,P值为0.001。SAI值对高阶像差的影响较SRI值大,尤其是SRI值较低的患者,RMSh值随SAI的增高而增大,主要表现为3阶彗差和4阶球差的增大。角膜形态为不规则形和不对称领结形时高阶像差最大,主要表现为三叶草和3阶彗差的增大。结论6.0mm瞳孔直径时,最主要的高阶像差是3阶彗差、三叶草和4阶球差。角膜形态为不规则形和不对称领结形时高阶像差最大。SAI对高阶像差的影响比SRI大。

Objective To investigate the distributive feature of higher order aherrations in myopic astigmatic patients and to analyze the influence of corneal topography on it. Methyls 434 eyes of 281 patients were objectively measured with wavescan wavefront system before laser in situ keratomileusis （LASIK） treatment. Corneal surface regularity index （SRI）, surface asymmetry index （ SAI ） and corneal shape were obtained by Tomey Corneal Topography （TMS-4）. Correlated analysis was performed between refractive power, SRI, SAI and the root mean square （RMS） of higher order aberrations, respectively. Enrolled eyes were divided into 5 groups by corneal shape. Rank run test was performed to compare the RMS within groups. Results The RMS of higher order aberrations （RMSh） was （0.286 ±0. 098 ） μm and decreased from third to six order aberrations across a 6.0ram pupil. Among these aberrations, the main comments were 3rd order coma, trefoil and 4th order spherical aberrations. The refractive power and SRI had no significant correlation with RMSh, Whereas, SAI had positive correlation with RMSh. Pearson coefficient was 0. 161 and P = 0.001. SAI had more influence on higher order aberrations than SRI. RMSh inereased with SAI especially when SRI was low, and the main increase was 3rd coma and 4th spherical aberrations. More RMSh was shown in the irregular pattern and asymmetry bow tie pattern than the other corneal shapes,and the main increase was trefoil and 3rd coma. Conclusion With a pupil diameter of 6. 0ram, the main high order aberrations of myopic astigmatic patients are 3rd coma, trefoil and 4th sphericalaberrations. More RMSh is shown in the irregular pattern and asymmetry bow tie pattern than the other corneal shapes. SAI has more influence on the higher order aberrations than SRI.