应用旋转Scheimpflug照相系统对角膜参数的研究

Investigation of corneal parameters using rotating Scheimpflug camera

目的以旋转Scheimpflug照相技术(Pentacam)研究角膜前表面曲率(Ra)、后表面曲率(Rp)及角膜厚度;根据测量结果,探讨角膜屈光力的计算方法。方法应用Pentacam对302名正常角膜的Ra、Rp、角膜厚度及测量所得K值(Km)进行测量,计算Rp与Ra比值(Rp/Ra)、角膜前表面屈光力(Ka)、后表面屈光力(Kp),以几何光学公式计算角膜屈光力(KO)与标定的角膜系数(Nc),对角膜各参数进行正态分布检验,直线回归分析Rp与Ra的相关性。结果各参数均服从正态分布。Ra为(7.74±0.26)mm,Ka为(48.62±1.61)D,CT为(0.545±0.036)mm,与既往报道的数据相似;角膜后表面参数与既往报道的数据及Gullstrand模型眼不同,Rp为(6.44±0.25)mm,Kp为(-6.22±0.24)D,Rp/Ra为0.832±0.017,低于Gullstrand模型眼的参数;Rp与Ra呈直线相关,回归方程为Rp=0.81×Ra+0.17(R2=0.71,P<0.05);Nc为1.3288±0.0010,低于标准的角膜系数1.3375。KO为(42.52±1.42)D,低于Km(43.64±1.44)D,差异有统计学意义(t=151.87,P<0.01)。K1.3288为(42.52±1.41)D,与KO比较差异无统计学意义(t=-0.052,P=0.96)。KO与K1.3288呈直线相关,回归方程为KO=1.006×K1.3288-0.241(R2=0.99,P<0.05)。结论旋转Scheimpflug照相技术与传统角膜地形图仪原理不同,应用该技术发现Rp、Kp、Rp/Ra及Nc与Gullstrand模型眼参数不同,对于标准化角膜光学模型及角膜屈光力的计算具有指导意义。

Background Traditional corneal parameters are derived from measurements of traditional instruments, keratometer or Placido-based topography. With the invention of a novel instrument,more reliable measurement can be achieved. Therefore ,reevaluation of the corneal parameters is necessary. Objective This study was to investigate the measuring results of corneal parameters using rotating Scheimpflug camera and to calibrate the method of keratometric power calculation. Methods Corneal parameters, including anterior corneal radius （ Ra ） , posterior corneal radius （ Rp ） and corneal thickness （CT） were measured in 302 normal eyes using Pentacam. The anterior corneal power （ Ka ） and posterior corneal power （ Kp ） , measured keratometrie power（ Km ） , Rp/Ra ratio, corneal optical power（ Ko ） and keratometric index（ Nc ） were analyzed according to the corneal optical properties. Normal distributions of these parameters were confirmed using One-Sample Kolmogorov-Smirnov Tests. The relation between R and R was correlated by linear-correlation. Results Ra ,K and CT revealed in this study,were（7.74 ± 0.26） mm, （48.62 ± 1.61） D and（0. 545 ±0. 036） mm,respeetively with analogous results to the previous publieations;Rp,Kp, Rp/Ra and Nc were（6.44 ±0.25） mm,（ -6.22 ±0.24） D,（0.832 ±0.017） and 1.328 8 ±0.001 0,respectively,showing different outcomes with that of the previous publications and the Gullstrand model eye. Linear correlation was found between Rp, and Ra,Rp =0.81 ×Ra ＋0. 17（R^2 =0.71,P〈0.05）.Nc（1.328 8 ±0.001 0） was lower than the standard ketratometric index （1. 337 5）. Ko was lower than Km calculated using standard Nc（42.52 ± 1.42 D versus 43.64 ± 1.44 D,t = 151.87,P 〈0. 01 ）. However,no statistically difference was found between Ko and Km calibrated by the calibrated Nc （1. 328 8） （42.52 ± 1.42 D versus 42.52 ± 1.41 D,t = -0. 052,P =0.96）. A positive linear eorrelationwas revealed between Ko and K1.3288 ,Ko = 1. 006 × K1 .3288 -0.241（R^2 =0.99,P 〈0.05）. Conclusion Rotating Scheimpflug camera offers some different corneal parameters with previous publications and Gullstrand model eye, indicating that standard Nc （ 1. 337 5 ） overestimates the corneal power ; while calibrated Nc revealed in this research can provide more accurate result.