Corneal topographer using null-screen patterned within a quadrangular acrylic prism

Abstract

In this paper, the use of four flat-null-screens forming a quadrangular prism setup is employed as a target for an experimental corneal topographer. Topographic maps of three reflective calibration spheres with different radii of curvature: 7.70 mm, 9.42 mm, and 6.20 mm, and the corneal surface evaluation of a volunteer subject are presented. The experimental setup is based on the null-screen method. Zonal reconstruction of the surface shape of the human cornea is obtained by numerical integration of the normal vectors. The corresponding elevation map was found fitting an spherical model to the recovered data. The differences obtained in radius of curvature were 0.02% or less for the calibration spheres, and the cornea under test showed a difference of 1.39% (0.6 diopters) compared to the value obtained with ORBSCAN topographer.