In this work, we use a null-screen corneal topographer with a semiradial spot pattern by using a mobile device’s camera to obtain images of the reflected pattern with the main aim of obtaining the corneal topography. First, we discuss how to integrate the system to calibrate it by testing a reference surface where we obtain optical parameters such as the radius of curvature and the conic constant, as well as elevation, sagittal curves, and meridional curvature maps with this method. Finally, we show some prelaminar measurements of the topography of some human corneas.
In this work, the topography of human corneas is evaluated with a conical corneal topographer based on the null-screen method. Geometrical parameters such as the radius of curvature and the conic constant, are obtained. Additionally, elevation, sagittal curvatures and meridional curvature maps can be calculated with the proposed method. Here, it is assumed that the shape of the cornea surface is an aspherical surface. To validate our proposal, we compare the results with those obtained by a commercial corneal topographer.
We extend the principles of the null-screen method for testing fast aspheric surfaces with polynomial expansion. We
present the formulae to design the null-screen in such a way that the image on the CCD is a perfect array circular points;
the departures of the surface from a perfect shape are observed as deformations of the array in the image. For the testing
of fast aspherics with polynomial expansion, we propose some geometrical configurations. In addition, we perform an
analysis of the deformations of the image of the null-screen reflected by the testing surface due to the slop defects of the
surface. Experimental results for the testing fast aspherics are shown. The main advantages and the limitations of the
method will be discussed.
In this work, we design a conical null-screen for testing non-symmetric corneas. We proposed a custom evaluation
algorithm in order to calculate the shape of the corneal surface. This data is fitting to a custom non-symmetrical shape
surface, taking into account orthogonal polynomials, in order to obtain the geometrical parameters such as the radius of
curvature and conical constant. In order to proof our proposal, we perform some corneal topography measurements.
In this work, we will present some improvements to the conical null-screen based corneal topographer, for testing aspheric surfaces without rotational symmetry. We present the formulae to design the conical null-screen in such a way that the image on the CCD is a perfect array of spots; departures from this geometry are due to deformation or misalignment of the surface. Additionally, we will explain how to improve the algorithms to find the normals of corneal surface. Finally, we will evaluate the topography of a spherical surface.
In this work, we propose some algorithms to recover the centroids of the resultant image obtained by a conical nullscreen
based corneal topographer. With these algorithms, we obtain the region of interest (roi) of the original image and
using an image-processing algorithm, we calculate the geometric centroid of each roi. In order to improve our algorithm
performance, we use different settings of null-screen targets, changing their size and number. We also improved the
illumination system to avoid inhomogeneous zones in the corneal images. Finally, we report some corneal topographic
measurements with the best setting we found.
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