In this work, we perform the characterization of a conical null-screen corneal topographer. For this, we design a custom
null-screens for testing a reference spherical surfaces with a radius of curvature of 7.8 mm. We also test a 1/2-inch (12.7
mm) diameter stainless steel sphere and an aspherical surface with a radius of curvature of 7.77 mm. We designed some
different target distributions with the same target size to evaluate the shape of the reference surfaces. The shape of each
surface was recovered by fitting the experimental data to a custom shape using the least square methods with an iterative
algorithm. The target distributions were modified to improve the accuracy of the measurements. We selected a
distribution and evaluate the accuracy of the algorithms to measure spherical surfaces with a radius of curvature from 6
mm to 8.2 mm by simulating the reflected pattern. We also simulate the reflected patter by changing the position of the
surface along the optical axis and then we measure the resulting radius of curvature.
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 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.
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 every optical testing method, the time taken to process data, the precision of the results and the sensitivity are among the most relevant aspects to be taken into account when the viability of its implementation is been under consideration. An accuracy and sensitivity analysis of a topographer based on a conical null-screen with a semi-radial distribution of targets is presented. On the other hand, we proposed a custom evaluation algorithm in order to reduce the time in the calculation of the normal to the corneal surface. Finally, we perform some corneal topographical measurements.
In this work we report the design of a null-screen for corneal topography. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with a novel radial points distribution drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Additionally, an algorithm to compute the sagittal and meridional radii of curvature for the corneal surface is presented. The sagittal radius is obtained from the surface normal, and the meridional radius is calculated from a function fitted to the derivative of the sagittal curvature by using the surfacenormals raw data. Experimental results for the testing a calibration spherical surface are shown. Also, we perform some corneal topography measurements.