A planning device for determining control data for a treatment apparatus for surgical correction of defective eyesight in an eye of a patient, wherein - the planning device generates the control data for the treatment apparatus comprising a laser device, which separates corneal tissue by irradiation of pulsed laser radiation, said laser radiation being focused on target points arranged in a pattern within the cornea, - the planning device comprises an interface for supplying measurement data on parameters of the eye, and defective-eyesight data on the eyesight defect to be corrected in the eye, - the planning device defines a volume using supplied measurement and defective-eyesight data, which volume is located within the cornea and whose removal from the cornea causes the desired correction of defective eyesight, - the planning device determines a boundary surface (19, 20), which confines the defined volume within the cornea, and - the planning device generates for said boundary surface (19, 20) a control dataset to control the laser device, which control dataset defines a three-dimensional pattern of the target points in the cornea, which are located in the boundary surface (19, 20) and are arranged such that the boundary surface (19, 20), after irradiation of the pulsed laser radiation according to the control dataset, is generated as a cut surface which isolates the defined volume in the cornea and, thus, makes it removable, characterized in that - the planning device composes the boundary surface from an anterior surface part and a posterior surface part, wherein one of the surface parts is located at a constant distance (d F) to an anterior surface of the cornea and the other surface part does not have a constant distance to the anterior surface. - the planning device generates the control data for the treatment apparatus comprising a laser device, which separates corneal tissue by irradiation of pulsed laser radiation, said laser radiation being focused on target points arranged in a pattern within the cornea, - the planning device comprises an interface for supplying measurement data on parameters of the eye, and defective-eyesight data on the eyesight defect to be corrected in the eye, - the planning device defines a volume using supplied measurement and defective-eyesight data, which volume is located within the cornea and whose removal from the cornea causes the desired correction of defective eyesight, - the planning device determines a boundary surface (19, 20), which confines the defined volume within the cornea, and - the planning device generates for said boundary surface (19, 20) a control dataset to control the laser device, which control dataset defines a three-dimensional pattern of the target points in the cornea, which are located in the boundary surface (19, 20) and are arranged such that the boundary surface (19, 20), after irradiation of the pulsed laser radiation according to the control dataset, is generated as a cut surface which isolates the defined volume in the cornea and, thus, makes it removable, characterized in that - the planning device composes the boundary surface from an anterior surface part and a posterior surface part, wherein one of the surface parts is located at a constant distance (d F) to an anterior surface of the cornea and the other surface part does not have a constant distance to the anterior surface.