The OPD-Scan III system is an integrated aberrometry system. It combines the attributes of a placido topographer, automated refractor, and automated keratometer, and adds the elements of wavefront aberrometry and pupillometry. By integrating these systems into one multifunctional unit, we can quantitatively evaluate how light is focused throughout the visual system. It provides us with both low-order aberrations, which in essence are the traditional refractive measures of sphere, cylinder (and axis), and high-order aberrations (such as spherical aberration, coma, trefoil, etc.). Furthermore, the OPD can identify the source of these aberrations and differentiate between external (typically anterior corneal and tear film) and internal aberrations (typically lenticular in origin, such as cataract, IOL anomalies, or posterior capsular opacities).