1. A method for the analysis of retinal vessels based on digital images comprising the steps of: arranging a ring-shaped measurement zone containing vessel portions which proceed from a central vessel and are to be measured and which differ in type between arteries and veins, said zone being arranged around the papilla at a distance therefrom; determining a vessel diameter for each of these vessel portions; calculating parameters from the determined vessel diameters of the vessel portions; selecting a series of adjoining vessel segments along the vessel portions; determining a vessel segment diameter and the associated image coordinates for every vessel segment; correlating the vessel segments to a vessel type distinguished by artery or vein and to a vessel portion; storing and archiving a data set comprising at least the coordinates of the vessel segment, the vessel segment diameter, the associated vessel type, the associated vessel portion, and a relatedness to the evaluated image for every vessel segment; determining, by patient-oriented comparison measurements in comparison images recorded with a time offset with respect to a reference image, the diameters of vessel segments in the comparison image which are identical to the vessel segments in the reference image, wherein the correlation of the vessel type and vessel portion to every vessel segment is adopted intact in the data set of the comparison image from the data set of the reference image, and wherein the data sets relating to the vessel segments in the comparison images are supplemented at least by the relatedness to the reference image; and using only identical vessel segments for which a vessel segment diameter can be determined in all of the comparison images and in the reference image for determining the data set in comparison measurements of the comparison images, and wherein absolute and relative differences between the reference image and the comparison image are generated for the vessel diameters and parameters.