1. An eye surgery microscopy system comprising: an imaging optic for generating an image of an object plane; an electronic image sensor for detecting said image of the object plane; a computer unit for computing the position of the center of a circular structure of a patient eye provided with at least one marking; said computer unit being further adapted to compute the position of the center of said circular structure by utilizing image processing via correlation with comparison information; said image sensor being connected to said computer unit; a plurality of comparison objects which, in said computer unit, are placed over said image of said object plane; each of said comparison objects being configured as a ring filter having an inner filter ring and an outer filter ring; said filter ring defining a filter function F r,(x z ,y z ) (x,y) having respectively different signs in said inner and outer filter rings; and, said computer unit being further adapted to determine said position of said center of said circular structure from values of filter responses determined from convoluting said image of said object plane and said filter function F r,(x z ,y z ) (x,y).