In the BAD all the curvature data for a specific diameter are used to calculate the radius of a reference surface (BFS) to evaluate height data – the goal is to detect suspicious elevation in the anterior and the posterior cornea. The EBFS uses curvature data for the same diameter as above, however it is excluding an area around the thinnest point (TP) of the cornea. In other words, the TP is detected; an area (usually 3.5 mm) around the TP is excluded in calculating the radius for the new reference surface. In a normal cornea the visual appearance of the maps does not differ between the BFS and the EBFS, but in an ectatic cornea where elevation (different curvature) will occur around the TP, excluding an area around the TP flattens the reference surface making it easier to visually detect early elevation.