Two classes of surgical keratometers are commercially available. The first class of devices produces a keratoscopic image from which the surgeon must make a qualitative assessment of both the amount and location of astigmatism based upon distortion present in the keratoscopic image. The second class of devices quantitates corneal power at a chosen meridian providing the surgeon with either an analogue or digital readout. Usually it is up to the surgeon to identify the meridian of greatest corneal power based on qualitative alterations of the keratoscopic image. These keratoscopes are based either on the optical principles of the von Helmholtz keratometer, or on nonparallel electronic image digitization.