A method for estimating a degree of contamination of a front screen of an optical detection apparatus is provided comprising the steps: Transmitting a plurality (p) of transmission radiation pulses into a detection zone; generating a reception signal for each transmission radiation pulse including a plurality (q) of sampled values, a sampled value indicating the intensity of the received back radiation of the transmission pulse after a predefined time interval from the transmission of the transmission radiation pulse; generating an averaged reception signal having a plurality (q) of sampled values from the plurality of reception signals, with those respective sampled values of the reception signals being added which were determined at mutually corresponding points in time to determine a sampled value of the averaged reception signal; generating at least one front screen contamination value by evaluating an amplitude value and/or a measured peak shape value of the averaged signal.