正常角膜前后表面散光的相关研究

目的:探讨全年龄正常人角膜前后表面散光的分布规律及角膜后表面散光对角膜总散光的影响。方法:分析4岁以上在天津市眼科医院就诊患者及欲进行白内障手术患者 571例（989眼）的Pentacam眼前节分析仪检查结果，记录角膜前后表面散光，总结角膜前后表面散光的分布规律及相关关系并分析角膜后表面散光对角膜总散光的影响。模拟角膜曲率计散光用屈光指数1.337 5及角膜前表面曲率半径计算，总角膜散光根据角膜前、后表面散光度数和轴位进行矢量分解计算。结果:（1）角膜后表面散光度数平均值为（0.34±0.16）D；34.8%（345眼）为顺归散光，62.5%（618眼）为逆归散光，2.6%（26眼）为斜轴散光。（2）角膜后表面散光度数与前表面散光度数正相关（r=0.576，P＜0.05)，角膜前后表面散光轴位呈正相关关系（r=0.381，P＜0.05）。（3）模拟角膜曲率计散光与角膜总散光大小分别为（1.21±0.76）D、（1.43±0.88）D，差异具有统计学意义（t=21.95，P＜0.01)；二者的散光轴位分别为（89.88±63.70）°、（89.29±61.53）°，差异无统计学意义（t=-1.08，P=0.28）。结论:角膜后表面散光度数很小，主要为逆规散光，其大小和轴位与角膜前表面散光均呈正相关；如果忽略角膜后表面散光，将会导致具有临床意义的角膜总散光的估计差异。

Study on anterior and posterior corneal astigmatism in normal cornea

Objective: To investigate the distribution of anterior and posterior corneal astigmatism and the effect of posterior astigmatism(PA) on total astigmatism (TA) in all ages of normal corneal human. Methods: A rotating Scheimpflug camera (Pentacam Oculus，Germany) was used to measure 989 eyes of 571 patients in Tianjin Eye Hospital. The anterior astigmatism (AA) and PA was recorded. The distribution and correlation of AA and PA were summarized and the effects of PA on TA were analyzed. The simulated keratometry astigmatism (KA) was calculated by the anterior corneal surface measurement and the index of 1.337 5，while TA was derived by anterior and posterior surface astigmatism and axial vector decomposition calculation. Results: （１） The mean PA was (0.34±0.16)D；with-the-role (WTR), against-the-role(ATR), oblique astigmatism of the posterior corneal surface were found in 345 eyes (34.8% ), 618 eyes （６2.5%） and 26 eyes（2.6%）.（2） The magnitudes of AA and PA were significantly correalated (Pearson correlation coefficient r=0.576，P＜0.05）. The axis of AA and PA were significant positive correlation（r=0.381，P＜0.05）.（３） The magnitude of TA and KA were （1.21±0.76）D and （1.43±0.88）D，respectively，with significant difference（t=21.95，P＜0.01）． The axis of TA and KA were（89.88±63.70）° and（89.29±61.53）°, respectively， without significant difference（t=-1.08，P=0.28）． Conclusion: The diopter of PA is mostly low and mainly with the axis ATR. There is significant positive correlation between the magnitude and axis of PA and AA; If PA is neglected, it will lead to clinically significant inaccuracies in estimation of the corneal astigmatism．