Placido disk methods for corneal topography use a target with concentric rings in order to obtain measurements of the corneal surface, codifying the topography from the deformations of the rings’ image. Knowing exactly how the corneal surface departs from a rotational symmetric shape is difficult by using Placido rings. This is due to the fact that any ray deviations in the angular direction (sagittal transverse aberrations) are not easily detected and measured. This is the so-called skew ray error. For that reason, this technique has been considered as limited, especially when one tries to measure corneal aberrations with large rotational symmetry errors. However, we considered that the Placido disk topography has the potential to obtain a full description of the corneal surface as long as the skew ray error is fixed. Here, we present a solution based in the assumption that a corneal topography calculated with the presence of the skew ray error has hidden information that can be extracted by applying some basis of the classical Hartmann test. To achieve that solution, we improve some aspects of the Hartmann test to be later applied in the processing of Placido disk images. Our solution gives us the ability to solve the skew ray error in a simple and direct method, with an effectiveness that is probed by the computing of some simulated representative surfaces without rotational symmetry and the performance of our algorithm.

中文翻译：

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具有非旋转对称像差的圆形Hartmann和Placido图案的区域积分。

用于角膜地形的Placido盘法使用具有同心环的目标，以获取角膜表面的测量值，从而根据环图像的变形来对地形进行编码。通过使用Placido环很难准确地知道角膜表面如何偏离旋转对称形状。这是由于以下事实：不容易检测和测量角度方向上的任何射线偏差（矢状横向像差）。这就是所谓的偏斜射线误差。因此，这种技术被认为是有限的，尤其是当人们试图测量旋转对称误差较大的角膜像差时。但是，我们认为只要固定斜线误差，Placido盘形地形图就有可能获得对角膜表面的完整描述。这里，我们基于以下假设提出了一种解决方案：在存在倾斜射线误差的情况下计算出的角膜地形图具有隐藏信息，可以通过应用经典Hartmann检验的某些基础来提取这些信息。为了实现该解决方案，我们改进了Hartmann测试的某些方面，以便稍后将其应用于Placido磁盘映像的处理中。我们的解决方案使我们能够以简单直接的方法解决偏斜射线误差，其有效性通过计算一些没有旋转对称性的模拟代表性表面以及我们算法的性能来探究。我们改进了Hartmann测试的某些方面，稍后将在Placido磁盘映像的处理中应用。我们的解决方案使我们能够以简单直接的方法解决偏斜射线误差，其有效性通过计算一些没有旋转对称性的模拟代表性表面以及我们算法的性能来探究。我们改进了Hartmann测试的某些方面，稍后将在Placido磁盘映像的处理中应用。我们的解决方案使我们能够以简单直接的方法解决偏斜射线误差，其有效性通过计算一些没有旋转对称性的模拟代表性表面以及我们算法的性能来探究。