1. A method of quantifying corneal topographic astigmatism (CorT) comprising, considering at least a portion of an eye of a patient to be divided into a multiplicity of concentric rings, forming a curved surface for each ring in which the curved surface conforms to a topography of the cornea of the respective ring, determining parameters of the cornea in each ring representative of the corneal topography of the ring, and vectorially summating the corneal parameters of all of the rings and obtaining a mean summated vectorial value representing a value of corneal topographic astigmatism (Cor TD) for said portion of the cornea of the eye of the patient.