title: A study of the accuracy of lens measures.
abstract: The accuracy of 26 aged and three new lens measures was investigated. Instruments were applied to surfaces of known curvature employing the conventional, hand-held method as well as while rigged on an optical bench. In addition, using the latter method, a controlled amount of surface tilt was introduced. A large inter-instrument variation in accuracy was encountered. In general, hand-held lens measures were found to provide equally accurate measurements on convex and concave surfaces, with the exception of the -20 D surface, and inclinations from 0 degree to 5 degrees did not result in erroneous measurements. Results for inclinations of 15 degrees became unreliable. The different usages of the instrument are discussed.
authors.affiliation: Department of Optometry & Visual Science, City University, London, UK.
authors.forename: O
authors.initials: O
authors.lastname: Hilton
authors.forename: H
authors.initials: H
authors.lastname: Obstfeld
mesh_terms: D004867:Equipment Design; D006801:Humans; D007908:Lens, Crystalline / Q000033:anatomy & histology*; D055095:Optics and Photonics; D009907:Optometry / Q000295:instrumentation*; D012680:Sensitivity and Specificity