光路追迹法计算角膜屈光手术后人工晶状体的屈光力

Calculation of intraocular lens power after corneal refractive surgery using ray tracing method

目的建立光路追迹法计算人工晶状体屈光力的方法,探讨其对角膜屈光手术后人工晶状体屈光力计算的准确性。方法根据眼屈光间质的特点以专业光学设计软件Zemax建立人工晶状体眼模型。对25例角膜屈光手术后白内障患者进行回顾性研究,以OrbscanⅡz或C-Scan测量角膜地形图,获得角膜前表面曲率,以IOL-Master测量眼轴长度。将所得参数及人工晶状体的参数输入光学设计软件Zemax,建立人工晶状体眼的光学模型,计算白内障手术后眼的屈光状态。以手术实际屈光状态为标准,计算二者间的差异为预测误差及预测误差的绝对值为绝对预测误差。统计学分析预测误差与绝对预测误差的平均值、标准差及分布。结果光路追迹法的预测误差为-1.09～1.91 D,平均预测误差为(0.28±0.73)D;绝对预测误差为0.01～1.91 D,平均绝对预测误差为(0.63±0.45)D。绝对预测误差≤0.5 D者9例(36%),0.5 D<绝对预测误差≤1.0 D者12例(48%),1.0 D<绝对预测误差≤1.5 D者3例(12%),1.5 D<绝对预测误差≤2.0 D者1例(4%),绝对预测误差≤1.0 D者21例(84%)。结论光路追迹法是以人工晶状体眼为光学模型计算人工晶状体的屈光力,可对计算角膜屈光手术后人工晶状体屈光力进行较为准确的计算。

Background The calculation of intraocular lens（IOL） power is important for cataract patient following corneal refractive surgery.Theoretically,ray tracing for intraocular lens calculation is an ideal method because pseudophakic optics can be imitated by this method.ObjectiveThis study is to introduce ray tracing method for IOL power calculation after corneal refractive surgery and evaluate the accuracy of ray tracing method.MethodsPseudophakic eye models to perform ray tracing calculations were constructed using optical software Zemax（Zemax-EE Optical Design Program,Focus Software,Inc.USA） by importing the corneal and IOL radii,refractive indexes of cornea,aqueous,IOL and vitreous.Ten eyes of Chinese patients and 15 eyes of German patients undergone corneal refractive surgery were enrolled in this study.Corneal radius was measured by Orbscan Ⅱ z or C-Scan.Axial length was measured by IOL Master or A-scan.The refraction after cataract surgery was predicted by ray tracing method.The difference between actual postoperative refraction and predicted refraction was defined as prediction error,and absolute value of prediction error was defined as absolute prediction error.The mean value,standard deviation and distribution of both prediction error and absolute prediction error were calculated using SPSS11.0 software.ResultsA pseudophakic eye model for IOL power calculation was constructed in this study.Mean prediction error was 0.28±0.73 diopter（D）（range-1.09 D to 1.91 D）;mean absolute prediction error was 0.63±0.45 D（range 0.01 D to 1.91 D）.For absolute prediction error,9 eyes（36%） were confined within 0.5 D;12 eyes（48%） were confined between 0.5 D and 1.0 D;3 eyes（12%） were confined between 1.0 D and 1.5 D;1 eye（4%） was confined between 1.5 D and 2.0 D.Totally 21 eyes（84%） were confined within 1.0 D.ConclusionRay tracing method is a reliable method for the calculation of intraocular lens power after corneal refractive surgery.