两种角膜前表面Q值计算方法的实验研究

The experimental research of two methods of calculation for the Q-value of corneal anterior surface

目的 比较正切图公式和弧矢图公式在非球面测试小珠前表面非球面系数（Q值）计算中的差别和准确性.方法 自身配对设计.利用莫尔金刚石车削机床加工制作不同前表面形态的非球面测试小珠共24个,用TalySurf粗糙度轮廓仪对其Q值和顶点曲率半径（r0）进行拟合.对24个非球面测试小珠进行OrbscanⅡ角膜地形图仪检查.采用配对t检验和Bland-Altman图一致性评价法,比较2种计算方法的准确性和稳定性.结果 ①用正切曲率半径和弧矢曲率半径计算所得24个非球面测试小珠0°半子午线的r0均值分别为（7.73±0.09）mm、（7.72±0.09） mm,数值上与拟合值[（7.70±0.08）mm]比较接近,但两者与拟合值的差异均有统计学意义（弧矢图：t=2.95,P＜0.01;正切图：t=4.45,P＜0.01）.②用正切曲率半径和弧矢曲率半径计算所得24个非球面测试小珠0°半子午线的Q值与拟合值的差异均无统计学意义（弧矢图：t=1.61,P＞0.05;正切图：t=-0.87,P＞0.05）.③用正切曲率半径计算所得24个非球面测试小珠的0°半子午线Q值与拟合值之差的均值较弧矢曲率半径更接近0,且95％一致性界限的上下限范围更小.结论 用正切曲率半径和弧矢曲率半径计算非球面系数均比较准确,但是用正切曲率半径计算角膜前表面非球面系数较弧矢曲率半径更为稳定.

Objective To compare the difference and accuracy of the two methods of calculation for the Q-value of corneal anterior surface that with tangential radius or sagittal radius.Methods Twenty-four aspheric test objects were manufactured with the Moore diamond turning lathe in this self-controlled study.The test objects were all verified by the TalySurf roughness profiler and the asphericity （Q） and vertex radius of curvature （r0） were fitted.Then,they were examined with the Orbscan Ⅱ corneal topography.The results were applied paired t-test and Bland-Altman figure to perform statistical analysis.Results ①The average r0-values of the horizontal semi-meridian calculated by the sagittal radius and the tangential radius were 7.72±0.09 mm,7.73±0.09 mm.Both of them were close to but have statistical differences with the fitted value 7.70±0.08 mm.②There was no statistical differences between Q-values of the horizontal semi-meridian calculated by the sagittal radius and the tangential radius and fitted value （sagittal refractive map：t=1.61,P〉0.05; tangent refractive map：t=-0.87,P〉0.05）.③The average differences between the Q-values of the horizontal semi-meridian calculated by the tangential radius and fetted values was more close to 0 than sagittal ones,and the 95% consistency limits of upper and lower range was smaller than sagittal ones.Conclusion Although the Q-values of corneal anterior surface calculated by tangential radius and sagittal radius are both reliable,the former is more accurate and stable.