Langenbucher Achim, Szentmáry Nóra, Cayless Alan, Wendelstein Jascha, Hoffmann Peter
Department of Experimental Ophthalmology, Saarland University, Kirrberger Str 100 Bldg. 22, 66424, Homburg/Saar, Germany.
Dr. Rolf M. Schwiete Center for Limbal Stem Cell and Aniridia Research, Saarland University, /Saar, Homburg, Germany.
Graefes Arch Clin Exp Ophthalmol. 2024 Feb;262(2):505-517. doi: 10.1007/s00417-023-06186-y. Epub 2023 Aug 2.
This study uses bootstrapping to evaluate the technical variability (in terms of model parameter variation) of Zernike corneal surface fit parameters based on Casia2 biometric data.
Using a dataset containing N = 6953 Casia2 biometric measurements from a cataractous population, a Fringe Zernike polynomial surface of radial degree 10 (36 components) was fitted to the height data. The fit error (height - reconstruction) was bootstrapped 100 times after normalisation. After reversal of normalisation, the bootstrapped fit errors were added to the reconstructed height, and characteristic surface parameters (flat/steep axis, radii, and asphericities in both axes) extracted. The median parameters refer to a robust surface representation for later estimates of elevation, whereas the SD of the 100 bootstraps refers to the variability of the surface fit.
Bootstrapping gave median radius and asphericity values of 7.74/7.68 mm and -0.20/-0.24 for the corneal front surface in the flat/steep meridian and 6.52/6.37 mm and -0.22/-0.31 for the corneal back surface. The respective SD values for the 100 bootstraps were 0.0032/0.0028 mm and 0.0093/0.0082 for the front and 0.0126/0.0115 mm and 0.0366/0.0312 for the back surface. The uncertainties for the back surface are systematically larger as compared to the uncertainties of the front surface.
As measured with the Casia2 tomographer, the fit parameters for the corneal back surface exhibit a larger degree of variability compared with those for the front surface. Further studies are needed to show whether these uncertainties are representative for the situation where actual repeat measurements are possible.
本研究采用自抽样法，基于Casia2生物特征数据评估泽尼克角膜表面拟合参数的技术变异性（根据模型参数变化）。
使用一个包含来自白内障患者群体的N = 6953次Casia2生物特征测量的数据集，将径向次数为10（36个分量）的条纹泽尼克多项式曲面拟合到高度数据上。拟合误差（高度 - 重建值）在归一化后进行100次自抽样。在归一化反转后，将自抽样得到的拟合误差添加到重建高度上，并提取特征表面参数（平/陡轴、半径以及两个轴向上的非球面度）。中位数参数用于稳健的表面表示，以便后续估计高度，而100次自抽样的标准差表示表面拟合的变异性。
自抽样得出角膜前表面在平/陡子午线上的半径和非球面度中位数分别为7.74/7.68毫米和 -0.20/-0.24，角膜后表面为6.52/6.37毫米和 -0.22/-0.31。前表面100次自抽样的相应标准差分别为0.0032/0.0028毫米和0.0093/0.0082，后表面为0.0126/0.0115毫米和0.0366/0.0312。与前表面的不确定性相比，后表面的不确定性系统性地更大。
使用Casia2断层扫描仪测量时，角膜后表面的拟合参数比前表面表现出更大程度的变异性。需要进一步研究以表明这些不确定性是否代表实际可进行重复测量时的情况。
