Optical sensor for determining a dialysis dose

A device for determining a dialysis efficiency/dialysis dose of an extracorporeal blood treatment with a radiation source, a cuvette, at least one detection unit and a regulation/control unit, wherein

• the radiation source is intended and configured to emit a radiation, the intensity of which is controlled/regulated by adjusting a current strength to which the radiation source is subjected,
• the cuvette is provided with a dialysis fluid inlet and a dialysis fluid outlet and is intended and configured to be penetrated by the radiation emitted by the radiation source,
• the detection unit is provided and adapted to detect, as a measurement detection unit, the intensity of the radiation after it has passed the cuvette,
• the regulation/control unit determines the dialysis efficiency/dialysis dose from the intensity of the radiation detected by the detection unit,
• wherein
• the regulation/control unit is connected to the radiation source and the detection unit and is provided and configured to reduce the intensity of the emitted radiation by adjusting the current strength over the time course of the extracorporeal blood treatment at least once, based on a decrease in a concentration of urinary substances in the dialysis fluid.