Næser Kristian, Savini Giacomo, Bregnhøj Jesper Flethøj
Regions Hospital Randers, Randers, Denmark.
Fondazione GB Bietti IRCCS, Rome, Italy.
Br J Ophthalmol. 2016 Sep;100(9):1196-200. doi: 10.1136/bjophthalmol-2015-307474. Epub 2015 Dec 23.
BACKGROUND/AIM: Keratometry measures the anterior corneal curvature only. Corneal power is calculated by multiplication with the keratometric refractive index, which takes into account the average negative posterior corneal power. The aim of this study was to calculate and compare various expressions for total corneal power assessed with Scheimpflug camera techniques, which also measure the posterior corneal curvature.
We used the Pentacam rotating Scheimpflug camera to measure the equivalent power, total corneal refractive power (based on Snell's law ray tracing), and simulated keratometry (keratometric refractive index=1.3375) over the central 3.0 mm zone in 951 eyes. The keratometric refractive index of the equivalent power and the total corneal refractive power was calculated as the ratio between these values and the anterior corneal curvature.
The equivalent power, total corneal refractive power, and simulated keratometry all differed statistically significantly (analysis of variance, p<0.001) and averaged 42.26 (±1.46) dioptres (D), 42.78 (±1.51) D and 43.42 (±1.49) D. The calculated keratometric refractive indices for equivalent and total corneal refractive power averaged 1.3284 (±0.0009) and 1.3324 (±0.0015). The error of using these calculated keratometric refractive indices rather than the measured values for equivalent and total corneal refractive power averaged 0 (±0.11 D) and -0.01 D (±0.19).
Pentacam rotating camera assessment of total corneal power over the central 3.0 mm zone differed significantly for simulated keratometry, equivalent power and Snell's law ray tracing.
背景/目的：角膜曲率计仅测量角膜前表面曲率。角膜屈光力通过与角膜曲率计屈光指数相乘来计算，该指数考虑了角膜后表面的平均负屈光力。本研究的目的是计算并比较使用眼前节分析系统技术评估的全角膜屈光力的各种表达式，该技术也可测量角膜后表面曲率。
我们使用Pentacam旋转式眼前节分析系统在951只眼中测量中央3.0 mm区域的等效屈光力、全角膜屈光力（基于斯涅尔定律光线追踪）和模拟角膜曲率（角膜曲率计屈光指数 = 1.3375）。等效屈光力和全角膜屈光力的角膜曲率计屈光指数计算为这些值与角膜前表面曲率之间的比值。
等效屈光力、全角膜屈光力和模拟角膜曲率在统计学上均有显著差异（方差分析，p<0.001），平均值分别为42.26（±1.46）屈光度（D）、42.78（±1.51）D和43.42（±1.49）D。等效屈光力和全角膜屈光力的计算角膜曲率计屈光指数平均值分别为1.3284（±0.0009）和1.3324（±0.0015）。使用这些计算的角膜曲率计屈光指数而非等效屈光力和全角膜屈光力的测量值的误差平均值分别为0（±0.11 D）和 -0.01 D（±0.19）。
Pentacam旋转相机对中央3.0 mm区域全角膜屈光力的评估在模拟角膜曲率、等效屈光力和斯涅尔定律光线追踪方面存在显著差异。
