Derivation of corneal flattening factor, p‐value

A mathematical equation was, derived to calculate the corneal p‐value based on the central and peripheral corneal radii and the corresponding semichord diameters. The calculation was simplified by a computer program written using GWBASIC. The accuracy of corneal p‐value generated from this program was checked with Douthwaite's modified keratometer with good correlation. This program could be used lo find out the corneal p‐value and apical radius ro for any topographic keratometer which only provides central and peripheral radii without any information of the p‐value and apical radius.