A system for performing a surgical procedure includes an OCT unit for scanning an object region volume with an OCT scanning beam and a control unit for setting the position of the object region volume. A surgical instrument having an effective section is arrangeable in an object region of the object region volume and is localizable in the object region volume with the OCT unit. A computer unit has a first computer program for determining the position of the effective section by processing scan information obtained by scanning the object region volume and a second computer program compares the scan information to reference data and provides a set value for the position of the effective section. The second computer program determines deviation information as to the spatial deviation of the effective section from the set value.