Quantitative descriptors of corneal shape derived from computer-assisted analysis of photokeratographs.

The goal of this retrospective study was to derive clinically useful quantitative measures of corneal shape from computer-assisted analyses of photokeratoscope photographs. Algorithms were developed to determine a new index of corneal symmetry, the Surface Asymmetry Index (SAI). The SAI correlated well with best spectacle-corrected visual acuity and may be useful clinically for predicting the level of spectacle-corrected visual acuity that could be expected based on the corneal surface topography in the otherwise normal eye of an individual patient. Algorithms were also developed to determine the centrally-weighted average corneal power and the power and location of the steepest and flattest corneal meridians. The average surface power and the power of the steepest meridian determined from the photokeratographs correlated well with values obtained using the keratometer in the retrospective series (correlation coefficient = 0.98 for the average surface power and 0.97 for the power of the steepest meridian).