1. A method for determining parameter of magnitude and meridian axis representing corneal astigmatism for use in vector analysis for diagnostic and surgical treatment, comprising the steps of: producing a keratometric map of topographic measurements of each of two semi-meridians of the cornea of an eye, assigning weighting values to the topographic measurements in each of a plurality of zones in each semi-meridian, and vectorially combining the weighted values of the topographic measurements to obtain a vector parameter in each semi-meridian representing magnitude and axis of topographic irregularity which is adapted for use in diagnostic and surgical treatment.