A head mountable device for measuring eye movement includes: a camera system comprising a first camera, wherein the camera system is configured to obtain a first set of images of a first eye of a user with a first frame rate and a first resolution; a processing unit configured to process the obtained first set of images and provide a processing unit output based on the first set of images; and an interface connected to the processing unit, for providing a device output based on the processing unit output; wherein the first frame rate is sufficient to allow the processing unit to detect eye saccades of the first eye.