Chapter two talks about the instruments that measure corneal surfaces, or in other words the topographers. Those instruments are discussed into two main categories: curvature based topographers, and elevation based topographers. The curvature based topographers are based on the principle of Placido disc or mires, keratometry, keratoscopy, photokeratoscopy and computerized videokeratoscopy; all the curvature based topographers are either projection based or reflection based. The elevation based topographers are based on the Scheimpflug image, which gives full information about the anterior and posterior corneal surfaces and corneal thickness or pachymetry. Thus, the elevation based are superior to the curvature based topographers since the latter gives information only about the anterior corneal surface. The Oculus Pentacam HR unit and its rotating Scheimpflug camera are also described in this chapter, with special concern of the Scheimpflug principle.