COMPARISON OF VIDEOKERATOSCOPE AND AUTOKERATOMETER MEASUREMENTS ON ELLIPSOID SURFACES AND HUMAN CORNEAS

BACKGROUND: Various studies have compared the accuracy and repeatabili ty of autokeratometers and videokeratoscopes using calibrated convex s urfaces. We investigate the agreement between the Topcon KR-3500 autok eratometer and the EyeSys videokeratoscope on human corneas and calibr ated convex surfaces. METHODS: Measurements were obtained from 30 conv ex ellipsoidal buttons and 20 right eyes of 20 young normal human subj ects. Vertex radius and p-values were compared for the two instruments . RESULTS: The two instruments showed excellent agreement on convex bu ttons. The human data showed no such relationship. For vertex radius, a good level of agreement was obtained only for surfaces whose p-value s were near unity. Repeatability was also calculated and was shown to be better with the Topcon autokeratometer than with the EyeSys videoke ratoscope. Editing the EyeSys data to encompass the same corneal area as that of the Topcon improved its repeatability, although it did not reach the level of the Topcon autokeratometer. CONCLUSIONS: The Topcon autokeratometer and the EyeSys videokeratoscope showed reasonable agr eement for surface topography on convex conicoidal plastic test button s but not for human corneas. Alterations in the data-capture mechanism s of videokeratoscopes could improve their ability to accurately image paraboloidal surfaces.