The invention relates to a planning unit for generating control data for a treatment device (1) for refractive correction during opthalmic surgery, said treatment device separating a corneal volume (21) that is to be removed from the surrounding cornea (5) for the correction, by means of a laser device (4) that penetrates at least one incised surface (20, 23) of the cornea (17), the planning unit (16) having at least one interface (29) to which corneal data concerning details of pre-operative incisions (30) carried out in a previous opthalmic surgical intervention can be supplied and calculation means for defining a corneal incision surface (22, 23) which delimits the corneal volume (21) to be removed. Said calculation means define the corneal incision surface (22, 23) on the basis of the corneal data and generate a control data record for the corneal incision surface (22, 23) in order to control the laser device (4).
