Characterization of test lenses for calibration of focimeters

Common ophthalmic lenses are simple spherical lenses which are only characterized within the first-order approximation of geometrical optics. First-order analysis provides the evaluation of focal length and related parameters. The back focal length serves to define the ophthalmic power and is measured by instruments called focimeters. The problem of characterizing test lenses for the calibration of focimeters is analysed. Measurement uncertainty is discussed in view of the necessity to comply with ISO recommendations. The most relevant quantity to be measured is the radius of curvature of lens refracting surfaces. Tables summarize the radius measuring capability that should be met by a laboratory in order to calibrate test lenses within the tolerances required. (Abstract quotes from original text)