An apparatus for the spatial localization of a moveable body part, in which the body part is situated inside a movement volume on the surface extending as far as to the inside of a living being. The apparatus includes: at least one optical recording apparatus outside the being, at least one meterable fluorophore which can be introduced in the region of the body part, an extrinsic radiation source which is arranged outside the being and from which radiation propagates in the direction of the movement volume, by way of which spectral excitation of the fluorophore takes place in that a wave emitted by the fluorophore is produced and can be determined at least at a wavelength which can be measured by the optical recording apparatus, the optical recording apparatus has at least one optical axis which can be oriented in the direction of the body part and the movement volume thereof, the optical recording apparatus has at least one optoelectric transducer which is perpendicular to the optical axis and outputs an output signal from which a distance between the fluorophore and a reference point can be determined.