基于Pentacam对角膜屈光指数的评价

目的：应用Pentacam测量角膜中央3 mm前表面曲率（Ra ）、后表面曲率（Rp）及中央角膜厚度（CCT）， 根据测量结果，探讨角膜屈光力及角膜屈光指数的计算方法。方法：系列病例研究。选取2017年2─10月在湘潭市中心医院和温州医科大学附属眼视光医院接受角膜屈光手术或白内障手术术前检查的患者419例（419眼）。术前采用Pentacam对眼前节进行检查，采集角膜中央3 mm Ra、RP及CCT 的相关数据，计算Ra与Rp比值（AP ratio）、角膜前表面屈光力（Ka ）以及后表面屈光力（Kp），按照厚 透镜高斯光学公式计算角膜总屈光力（KGOF）及角膜屈光指数（Ncal）。采用配对样本t检验比较各种K 值之间的差异。结果：Pentacam测量所得Ra、Rp、Rsimk、CCT、SimK分别为（7.73±0.27）mm、（6.34± 0.24）mm、（7.73±0.27）mm、（537±33）μm、（43.65±1.52）D。AP ratio为1.220±0.026，角膜屈光指数 Ncal为1.328±0.001。结论：利用Pentacam测量角膜参数计算所得角膜屈光指数可以提高角膜总屈光力及角膜后表面屈光力预算的准确性。

Evaluation of the Keratometric Index by the Pentacam

Objective: To calculate the total corneal power and the keratometric index based on actual measurements of the anterior and posterior corneal surfaces and the central corneal thickness by Pentacam and evaluate the accuracy of this keratometric index in estimating total and posterior corneal powers. Methods: This was a series case study. Four hundred and nineteen patients (a total of 419 eyes) who had undergone preoperative examination and laser in situ keratomileusis (LASIK) surgery or cataract surgery from February to October 2017 at the Xiangtan Central Hospital and Eye Hospital, Wenzhou Medical University were chosen for the study. The radius of the best-fit sphere for the anterior corneal surface (Ra) and posterior corneal surface (Rp), and central corneal thickness (CCT) were obtained. The ratio of Ra to Rp (AP ratio), anterior corneal power, posterior corneal power and keratometric index were calculated, and the total corneal power in each eye was calculated using the Gaussian optics formula. A paired-samples t-test was used to compare the difference in K values. Results: The means for Ra, Rp, Rsimk, CCT and SimK were 7.73±0.27 mm, 6.34±0.24 mm, 7.73±0.27 mm, 537±33 μm, and 43.65±1.52 D, respectively. The mean calculated AP ratio was 1.220±0.026. The mean calculated keratometric index (Ncal) was 1.328±0.001. Conclusions: The Pentacam-derived keratometric index improves the predictive accuracies of total and posterior corneal powers.