Preussner Paul-Rolf, Hoffmann Peter, Wahl Jochen
University Eye Hospital , Mainz , Germany , and.
Curr Eye Res. 2015;40(8):809-14. doi: 10.3109/02713683.2014.959708. Epub 2014 Sep 26.
To quantify the impact of posterior cornea on toric IOL calculation accuracy using Placido-topography of anterior corneal surface and Scheimpflug measurements of corneal thickness.
Three-hundred seventy-nine non-selected eyes undergoing cataract surgery with non-toric intraocular lens (IOL) implantation were measured with TMS-5 (Tomey, Japan), IOLMaster (Zeiss, Germany) and Lenstar (Haag-Streit, Switzerland). Anterior, posterior and total measured corneal astigmatisms were compared with astigmatisms from postoperative refraction by calculating vector differences.
The average absolute vector difference between anterior astigmatism and total astigmatism combining the measurements of anterior and posterior cornea was only 0.3 ± 0.2 D, with a median of only 0.27 D, but a maximum of 1.5 D. Measurements of anterior cornea alone show a systematic difference from refractive cylinder of 0.3-6 D at 90, 0.38 D at 89° and 0.28 D at 91° (IOLMaster, Lenstar and anterior TMS5), whereas the total TMS5 cylinder differs on average by only 0.14D at 81° from the refractive cylinder. With-the-rule (WTR) corneal astigmatism is slightly reduced and against-the-rule (ATR) astigmatism slightly increased on average when posterior corneal surface is taken into account additionally. This could also be confirmed by the calculation of an average pachymetry of all eyes in which the thinnest central part shows an ellipsoidal shape with horizontally long axis.
Measurements of posterior cornea have on average only a small but significant impact on the outcome of toric IOL calculation, however, they are nevertheless recommended to detect outliers in which corneal irregularities (e.g. beginning keratokonus) may be overlooked.
利用前角膜表面的Placido地形图和角膜厚度的Scheimpflug测量值，量化后角膜对散光人工晶状体（IOL）计算准确性的影响。
使用TMS-5（日本多美）、IOLMaster（德国蔡司）和Lenstar（瑞士哈格施特赖特）对379例行非散光人工晶状体植入白内障手术的未筛选眼睛进行测量。通过计算矢量差，将测量的前、后角膜散光和总角膜散光与术后验光得到的散光进行比较。
前散光与结合前、后角膜测量值的总散光之间的平均绝对矢量差仅为0.3±0.2D，中位数仅为(0.27D)，但最大值为(1.5D)。仅测量前角膜时，与90°处的屈光柱镜有(0.3 - 6D)、89°处有(0.38D)以及91°处有(0.28D)的系统差异（IOLMaster、Lenstar和前TMS5），而总TMS5柱镜与屈光柱镜在81°处平均仅相差(0.14D)。额外考虑后角膜表面时，顺规（WTR）角膜散光平均略有降低，逆规（ATR）散光平均略有增加。这也可以通过计算所有眼睛的平均角膜厚度来证实，其中最薄的中央部分呈水平长轴的椭圆形。
后角膜测量平均对散光IOL计算结果的影响虽小但显著，不过仍建议进行测量以检测可能被忽视的角膜不规则情况（如早期圆锥角膜）的异常值。
