Abstract: A wearable device may include a head-mounted display (HMD) for rendering a three-dimensional (3D) virtual object which appears to be located in an ambient environment of a user of the display. The relative positions of the HMD and one or more eyes of the user may not be in desired positions to receive, or register, image information outputted by the HMD. For example, the HMD-to-eye alignment vary for different users and may change over time (e.g., as a given user moves around or as the HMD slips or otherwise becomes displaced). The wearable device may determine a relative position or alignment between the HMD and the user's eyes. Based on the relative positions, the wearable device may determine if it is properly fitted to the user, may provide feedback on the quality of the fit to the user, and may take actions to reduce or minimize effects of any misalignment.