Authors: Leonidas Traipe Magdalena Rios Edison Villagra Allister Gibbons Marcelo Hidalgo Claudia Goya Authors have no financial interest They represent the true shape of the cornea independent of the position of the corneal surface to the visual axis. They provide more precise results than curvature maps Curvature maps assume that the visual axis and reference axis pass through the apex of the cornea To describe the variation in elevation topography that happens when the body of reference is changed in a Scheimpflug based system using Allegro Oculyzer (Wavelight Inc.). To determine specific differences between: Best fit Sphere Ellipsoid Toric Ellipse Sample: We retrospectively analyzed 90 consecutive keratoconus patients (149 eyes), diagnosed by clinical and topographical criteria. 72.2% Male // years old The sample was divided in 4 different stages described by Krumeich (1998) and later modified by Alio (2006). Eyes: Stage I=55 // Stage II=44 // Stage III=25 // Stage IV=25 KRUMEICH J, DANIEL J, KNLLE A Live-epikeratophakia for keratoconus. J Cataract Refract Surg. 24: ALIO J, SHABAYEK M Corneal Higher Order Aberrations: A method to grade keratoconus. J Refract Surg. 22: Analysis Plot Points of elevation (in micrometers) over/under the body of reference in the central 3 mm. Valid for the anterior and posterior surface (Belin M, 2005). We used constant distances between each of the 9 points analyzed in each patient. We did not modify the axis of reference of the topographic maps. 8,00 3,57 0,00 6,00 -1,02 -10,00 11,00 2,05 -5,00 9,00 2,55 -3,00 9,00 -0,91 -8,00 10,00 0,36 -7,00 8,00 1,76 - 4,00 6,00 0,02 -6, ,00 4,40 -1, Red = Minimum value of elevation. Blue = Maximal value of elevation. White = Mean value of elevation. This procedure was applied to all eyes included in this sample. For each body of reference and for both corneal surfaces. Elevation Point Analyzed Body of reference with statisticall diferences in comparison with the other bodies. P- value Anterior SurfacePoint 1 (Central) BFS Toric Ellipse