The cornea is the outermost surface of the eyeball; and has almost 70% of the eyes total refractive power, what makes it essential for the human vision process. However, some pathologies and refractive errors modify normal functions of the cornea, decreasing visual acuity along with the individual's quality of life. Thus, in the presence of ametropia, an appropriate diagnosis, treatment, and corrections of cornea's dimensions is vital. Nowadays, several methods to retrieve corneal topography are available. In this paper, the most relevant techniques in the field are presented.

In this article, the use of a square Hartmann screen test to measure the radius of curvature of a corneal topography calibration test sphere is presented. The proposed technique is based on the image formation principle by specular reflection on convex reflective surfaces. Applying an inverse Hartmann test, a de-magnified virtual image (Hartmanngram) is obtained; considering their own scaled reference screen plate, a zonal wavefront retrieval approach is used and the radius of curvature obtained. Experimental setup along the obtained results is presented. A simulated spherical wavefront is used as a method to evaluate the error in the wavefront reconstruction. Since the measurements of radius of curvature fits in to ISO 10343, through suitable modifications the proposed method is potentially applicable in small F/# convex specular surfaces, as is the case in keratometry and corneal topography measurements.