Oshika T, Tomidokoro A, Tsuji H
Department of Ophthalmology, University of Tokyo School of Medicine, Tokyo, Japan.
Exp Eye Res. 1998 Oct;67(4):443-7. doi: 10.1006/exer.1998.0558.
The refractive status of the posterior corneal surface has not been well studied. The purpose of this study is to quantitatively evaluate the regular and irregular astigmatism of the posterior corneal surface. In 50 normal human eyes, topography of the anterior and posterior corneal surface was measured with the scanning-slit videokeratoscope. Using Fourier series harmonic analysis, dioptric data on a mire ring were decomposed into spherical component, regular astigmatism, asymmetry (tilt or decentration), and higher order irregularity. The obtained values for the central 3.0 mm of the posterior corneal surface were -6.55+/-0.32 D (spherical component), 0.18+/-0.16 D (regular astigmatism), 0.40+/-0.22 D (asymmetry), and 0.02+/-0.02 D (higher order irregularity). The posterior to anterior ratios of these parameters were 13.6+/-0.6%, 35.0+/-41.3%, 45.8+/-56.9%, and 39.9+/-39.8%, respectively. The ratio of the spherical component was significantly lower than the other three parameters (P<0.001, Wilcoxon signed-rank test), indicating that non-spherical components (regular and irregular astigmatism) of the posterior corneal surface are not negligible in the optical quality of the cornea. The current results can serve as the control data and reference for the future clinical studies of optical characteristics of the cornea as a whole.
角膜后表面的屈光状态尚未得到充分研究。本研究的目的是定量评估角膜后表面的规则和不规则散光。对50只正常人类眼睛，使用扫描裂隙式角膜地形图仪测量角膜前、后表面的地形图。利用傅里叶级数谐波分析，将视标环上的屈光数据分解为球镜成分、规则散光、不对称性（倾斜或偏心）和高阶不规则度。角膜后表面中央3.0 mm区域获得的值分别为-6.55±0.32 D（球镜成分）、0.18±0.16 D（规则散光）、0.40±0.22 D（不对称性）和0.02±0.02 D（高阶不规则度）。这些参数的后表面与前表面比值分别为13.6±0.6%、35.0±41.3%、45.8±56.9%和39.9±39.8%。球镜成分的比值显著低于其他三个参数（P<0.001，Wilcoxon符号秩检验），表明角膜后表面的非球镜成分（规则和不规则散光）在角膜光学质量中不可忽略。目前的结果可作为未来整个角膜光学特性临床研究的对照数据和参考。
