A wearable computing device or a head-mounted display (HMD) may be configured to track the gaze axis of an eye of the wearer. In particular, the device may be configured to observe movement of a wearer's pupil and, based on the movement, determine inputs to a user interface. For example, using eye gaze detection, the HMD may change a tracking rate of a displayed virtual image based on where the user is looking. Gazing at the center of the HMD field of view may, for instance, allow for fine movements of the virtual display. Gazing near an edge of the HMD field of view may provide coarser movements.