Figure 1-15 (continued) C, Corneal tomography image using dual Scheimpflug/Placido–­based technology. The surface curvature, pachymetry, and anterior and posterior elevation mappings are shown. Numerical values appear along the right side. D, Wavescan image from a device like that illustrated in Fig 1-2A, taken of the fellow eye of the one seen in parts A, B, and C. Note that this map does not show corneal surface contours or features but rather provides information about the optics of the entire ocular system. As such, it can provide information on the refractive error and aberrations of the entire eye. (Courtesy of M. Bowes Hamill, MD.)

Figure 1-16 Height maps (typically in $ \mu\mathrm{m} $). A, Height relative to plane surface; $ z_{1} $ is below the surface parallel to the corneal apex, and $ z_{2} $ is above the surface parallel to the corneal limbus. B, Height relative to reference sphere; $ z_{3} $ is below a flat sphere of radius $ r_{1} $, and $ z_{4} $ is above a steep sphere of radius $ r_{2} $. (Illustration by Christine Gralapp.)

Figure 1-17  ​Scheimpflug tomography difference maps demonstrating corneal power change before and ­after myopic LASIK. (Courtesy of Karolinne Maia Rocha, MD, PhD.)

Figure 1-18  ​Postablation topographic maps. A, Small optical zone ­after excimer ­laser ablation; B, decentered ablation. (Courtesy of J. Bradley Randleman, MD.)