The eye of the patient is observed by the surgeon using a microscope equipped for the specific purpose. An eye tracker follows the motion of the operated eye. The microscopic image of the object plane is covered with a pattern by a pattern generator. The outer contour and the inner contour of the cornea are represented as circles (125, 127) provided with a multitude of miniature circles (121, 123) positioned along both of the lines (125, 127). The micro-circles (121, 123) can be used by the surgeon for creating a regular zigzag stitch pattern (131).