Jin Ying-Ying, Zhou Zhen, Yuan Xiao-Yong, Song Hui, Tang Xin
Tianjin Medical University, Tianjin 300070, China.
Clinical College of Ophthalmology, Tianjin Medical University, Tianjin Eye Hospital, Tianjin 300020, China.
Int J Ophthalmol. 2018 Jun 18;11(6):958-965. doi: 10.18240/ijo.2018.06.10. eCollection 2018.
To explore the effect of the posterior astigmatism on total corneal astigmatism and evaluate the error caused by substituting the corneal astigmatism of the simulated keratometriy (simulated K) for the total corneal astigmatism in age-related cataract patients.
A total of 211 eyes with age-related cataract from 164 patients (mean age: 66.8±9.0y, range: 45-83y) were examined using a multi-colored spot reflection topographer, and the total corneal astigmatism was measured. The power vector components J and J were analyzed. Correlations between the magnitude difference of the simulated K and total cornea astigmatism (magnitude difference), anterior J, and absolute meridian difference (AMD) between the anterior and posterior astigmatisms were calculated. To compare the astigmatism of the simulated K and total cornea both in magnitude and axial orientation, we drew double-angle plots and calculated the vector difference between the two measures using vector analysis. A corrective regression formula was used to adjust the magnitude of the simulated K astigmatism to approach that of the total cornea.
The magnitude difference was positively correlated with the anterior corneal J (Spearman's rho= 0.539; <0.001) and negatively correlated with the AMDR (Spearman's rho=-0.875, <0.001). When the anterior J value was larger than 1.3 D or smaller than -0.8 D, the errors caused by determining the total corneal astigmatism with the karatometric calculation tended to be greater than 0.25 D. An underestimation by 16% was observed for against the rule (ATR) astigmatism and an overestimation by 9% was observed for with the rule (WTR) astigmatism when ignoring the posterior measurements.
Posterior corneal astigmatism should be valued for more precise corneal astigmatism management, especially for higher ATR astigmatism of the anterior corneal surface. We suggest a 9% reduction in the magnitude of the simulated K in eyes with WTR astigmatism, and a 16% addition of the magnitude of the simulated K in eyes with ATR astigmatism.
探讨后表面散光对总角膜散光的影响，并评估在年龄相关性白内障患者中用模拟角膜曲率计（模拟K）的角膜散光替代总角膜散光所引起的误差。
使用多色光斑反射角膜地形图仪对164例患者（平均年龄：66.8±9.0岁，范围：45 - 83岁）的211只年龄相关性白内障眼进行检查，测量总角膜散光。分析屈光力矢量分量J0和J四十五。计算模拟K与总角膜散光的量值差（量值差）、前表面J0以及前后表面散光之间的绝对子午线差（AMD）之间的相关性。为了比较模拟K和总角膜散光在量值和轴向方向上的差异，我们绘制了双角图，并使用矢量分析计算了两种测量方法之间的矢量差。使用校正回归公式调整模拟K散光的量值，使其接近总角膜的量值。
量值差与角膜前表面J0呈正相关（Spearman秩相关系数=0.539；P<0.001），与AMDR呈负相关（Spearman秩相关系数=-0.875，P<0.001）。当前表面J0值大于1.3 D或小于-0.8 D时，用角膜曲率计计算确定总角膜散光所引起的误差往往大于0.25 D。忽略后表面测量时，逆规（ATR）散光低估16%，顺规（WTR）散光高估9%。
为了更精确地管理角膜散光，应重视后表面角膜散光，特别是对于角膜前表面较高的ATR散光。我们建议，对于WTR散光眼，将模拟K的量值降低9%；对于ATR散光眼，将模拟K的量值增加16%。
