A device (1300) adapted to be worn by a user is disclosed, comprising an optical element, a light source and a sensor. The optical element is adapted to be arranged in front of an eye (1312) of the user and formed of a light-transmitting material allowing the user to see through the optical element, wherein the light source is arranged on the optical element and adapted to illuminate at least a part of the eye of the user. Further, the sensor is adapted to capture light which has been emitted from the light source and reflected on the eye. A system for is also disclosed, comprising such a device and a processor adapted to determine a gaze direction of the user based on the light captured by the sensor.