Olympus developed a very small Head mounted display that is meant to be worn at all times.
The HMD is augmenting contextual information on top of what the wearer sees without impairing vision. The projected screen measures 10cm and is 50cm away. The HMD itself measures only 3.2 mm x 3.2 mm x 27 mm and weighs 27g.
We reported about the Scalar Teleglasses which are weighing just 7g, but are seeming to be more obtrusive mounted in front of the eye, impairing vision.
More details on Nikkei's Tech-On.