Corneal Topography, Keratometry and Contact Lenses

Keratometry: A Review

“…The recalculated power may be appropriate for the refracted beam entering the eye, but Goldberg's theme is the unsuitability of the keratometer for contact lens fitting, and insofar as the keratometer readings are correct, if they had been expressed in radius terms in the first instance then they would have been directly comparable with the lens radii of curvature according to current fitting procedures. Soper, Sampson and Girard (1962) and Sampson, Soper and Girard (1965) described a system of peripheral keratometry like that of Mandell for determining the extent of the optic cap, but they disregarded measurement errors completely and did not even quantify the change in power marking the boundary of the optic cap, merely defining the boundary as "the points on the corneal surface where the radius of curvature begins flattening." Black (1965), in discussion on the second of these papers, reported that in his experiments using a similar method, errors of 0.5 mm occurred in locating the position of areas of changing curvature, and that a keratometer could be considered to have an accuracy of 1/12D in power.…”