A system is derived which permits evaluation of the corneal curvature. It relates the instrumental conditions of the photokeratoscope, the first derivative, instantaneous radius of the point on the surface forming the reflected image, and the position of the surface as determined by focusing upon this image. The experimental data obtained from a photograph of the reflected image can be used to test the validity of any hypothesized expression for the corneal contour. For the first time a proposed analytic form can be used directly in the evaluation, thus minimizing recourse to simplifying, but distorting, assumptions. The system is nonspecific and may be applied to the analysis of other aspheric surfaces. Its application to a nonphotographic technique of corneal measurement is presented.
SIDNEY WITTENBERG and WILLIAM M. LUDLAM, "Derivation of a System for Analyzing the Corneal Surface from Photokeratoscopic Data," J. Opt. Soc. Am. 56, 1612-1615 (1966)