基于椭球面拟合的人眼角膜前表面面型参数

摘要

Objective To study the parameters of the anterior corneal surface in Chinese eyes based on the collection of raw elevation data of the surface using the ellipsoid fitting method.Methods Eighty eyes were included in this experimental study.The Levenbery-Marquardt method was used to fit the elevation data.The parameters of the anterior corneal surface were obtained by coordinate transformation and rotation processing.Spherical fitting,conic fitting and biconic fitting were also used to obtain the parameters of the anterior corneal surface for t test comparisons.Results The root mean square fitting error with ellipsoid fitting was as low as 2.14±0.56 μm for an 8 mm fitting diameter,and the standard deviation was only 0.56 μm,showing good reliability.However,the fitting error and fitting reliability for other fitting methods were inferior to ellipsoid fitting.For ellipsoid fitting,the radius of the anterior corneal surface was 7.67±0.23 mm,and the corresponding refractive power of the anterior corneal surface was 49.02±1.44 D.The Q-value of the anterior corneal surface was-0.33±0.09.The refractive power obtained with other fitting methods was higher than the refractive power obtained from the ellipsoid fitting (P＜0.01) whereas the absolute obtained Q-value was lower than that obtained from the ellipsoid fitting (P＜0.01).Conclusion This study shows that the actual anterior corneal refractive power is higher than the widely accepted anterior corneal refractive power of 48 D and the anterior corneal surface is more prolate than expected.%目的 采用椭球面角膜前表面面型研究中国人角膜的实际面型参数.方法 实验研究.选取40例(80眼)屈光手术前检查患者,用Levenberg-Marquardt方法对测量得到的角膜高度数据进行拟合,然后再通过坐标变换,得出角膜的参数.另外,采用t检验比较了球面拟合、旋转对称非球面拟和以及双二次曲面拟合下的角膜面型参数.结果 采用椭球面拟合,8 mm直径范围的均方根值低达(2.14±0.56) μm;拟合的稳定性好,标准偏差只有0.56 μm;而其他拟合方式均远低于以上的拟合精度.椭球面拟合时,角膜前表面曲率半径的平均值为(7.67±0.23)ram,相应的屈光度为(49.02± 1.44)D;角膜前表面的非球面系数(Q值)的平均值为-0.33±0.09;其他拟合方式下得到的曲率半径均比椭球面拟和的大(P＜0.01),而角膜前表面Q值的绝对值小于椭球面拟和下的Q值(P＜0.01).结论 角膜的实际屈光度较目前的公认值48 D大,而角膜的实际面型也更为扁长.