We propose the design of a conical null-screen with quasi-elliptical targets drawn on it so that its image, which is formed by reflection on a biconical convex surface, becomes a precise radial set of circular targets if the surface under test is perfect. This null-screen avoids alignment difficulties of the test system due to the contour of the face (eyebrows, nose or eyelids). In addition, the proposed method prevents the targets from overlapping and touching each other. We discuss how to integrate the system to calibrate it by testing a spherical and a biconical surface on which we obtain geometrical parameters such as radius of curvature and conic constant, as well as elevation, and sagittal and meridional curvature maps with a smartphone-based corneal topographer.
In this work we report the design of a conical corneal null-screen compact topographer, which uses a mobile device to capture null-screen reflection produced by the posterior corneal surface. The instrument features a head holder like those of virtual reality headset with the aim of align the topographer. For corneal topography the device is calibrated by testing a reference surface where the geometrical parameters such as the radius of curvature and the conic constant, are obtained. We present examples of surface topography measurements on 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.
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