New corneal shapes in keratorefractive surgery.

The corneal shape change as measured by the Humphrey keratometer and the corneascope after radial keratotomy in 50 patients was compared. The Humphrey keratometer analyzes a unique curve fit algorithm of the aplanatic corneal surface and designates this comparison as a shape factor. Both the corneascope photographs and the Humphrey keratometer demonstrated central corneal flattening after successful radial keratotomy. In addition, the normal "plus" shape factor was routinely converted to a "negative" shape factor after the procedure. This is analogous to converting the aplanatic central cornea, which normally approximates the end of an ellipse, to a topography which appears in cross section as the side of an ellipse. This alteration in topography is directly correlated to the magnitude of cycloplegic refractive change seen with this operation. The corneascope map topography of the cornea confirms this alteration in curvature.