Head-mounted display (HMD) devices can be used in various applications, including military, aviation, medicine, video gaming, entertainment, sports, and so forth. See-through HMD devices allow the user to observe the physical world, while optical elements add light from one or more small microdisplays into the user's visual path, to provide an augmented reality image. Similarly, immersive HMD devices provide an augmented reality image while the user is closed off from the physical world.