A planning system for generating control data, a treatment device for ophthalmic surgery to correct refraction, and a method for generating control data for such a treatment device, the method enabling easy continuation of an interrupted treatment or correction of a previous treatment. To this end, the planning system has a calculating device configured to define a corneal incision surface, wherein the calculating device determines the new corneal incision surface such that the existing corneal incision surface is incised by at least a part of the new corneal incision surface at an angle of between 60° and 120°.