A device for protecting tissue when treating an eye using a laser beam generated by a laser system and deflected by a scanner system comprises an eye model, a control data module and a processor. The eye model comprises eye data which define dimensions and locations of eye structures. The control data module is configured to register control data which define beam parameters of the laser beam and a scanning pattern for the laser beam. The processor is configured to simulate by computation a light spot moving on or in an eye structure on the basis of the eye data and the control data, to add up, for a plurality of measurement points of the eye structure and continuously, a beam dose emitted at the relevant measurement point by the moving light spot and to generate an emergency signal if a dose limit Dmax is exceeded at one of the measurement points.
