Fig. 7. Five qualitative patterns of normal corneal topography using a normalized scale. Top left, round; top center, oval; top right, symmetric bow-tie; bottom left, = asymmetric bow tie; bottom center, irregular. In the normalized scale (bottom right) the range of dioptric power represented by each color varies among eyes, depending on the degree of corneal asphericity. (Courtesy of Bogan SJ, Waring GO, Ibrahim O et al: Classification of normal corneal topography based on computer-assisted videokeratography. Arch Ophthalmol 108:945–9, 1990.)