A subject is illuminated whose movements of at least one eye are to be registered by an eye-tracker for producing resulting data. To this aim, a coherent light source in light producing means produces at least one well-defined light beam. A diffractive optical element is arranged between the coherent light source and an output from the light producing means. The diffractive optical element is configured to direct a light beam towards at least a first designated area estimated to cover the at least one eye of the subject. Image registering means registers light from the at least one light beam having been reflected against the subject. The resulting data is produced in response to these light reflections, which resulting data represents movements of the at least one eye of the subject.