A review of methods for measuring corneal topography.

A review of some methods and their optical principles for measuring the corneal topography are presented in this paper. The concepts of principal curvatures and the ambiguity concerning the axial curvature of surfaces without symmetry of revolution are analyzed. These methods are divided into three groups according to the following optical principles: (1) specular reflection, which includes the Placido disk system, interferometry, and moiré deflectometry; (2) diffuse reflection, which includes moiré fringes, rasterstereography, and Fourier Transform Profilometry; and (3) scattered light, which includes the slitlamp system. We avoided describing the details of commercial instruments, only their working principles.