Virtual reality
Around the same time, Douglas Engelbart used computer screens both as input and output devices. In 1968, Ivan Sutherland, with the help of many students including Bob Sproull, created what was widely considered to be the first head-mounted display (HMD) system for use in immersive simulation applications. It was primitive both in terms of user interface and realism, and the HMD to be worn by the user was so heavy that it had to be suspended from the ceiling. The graphics comprising the virtual environment were simple wire-frame model rooms. The formidable appearance of the device inspired its name, The Sword of Damocles.
Virtual retinal display
The VRD was invented by Kazuo Yoshinaka of Nippon Electric Co. in 1986. Later work at the University of Washington in the Human Interface Technology Lab resulted in a similar system in 1991. Most of the research into VRDs to date has been in combination with various virtual reality systems. In this role VRDs have the potential advantage of being much smaller than existing television-based systems. They share some of the same disadvantages however, requiring some sort of optics to send the image into the eye, typically similar to the sunglasses system used with previous technologies. It also can be used as part of a wearable computer system.
A Washington-based startup, MicroVision, Inc., has sought to commercialize VRD. Founded in 1993, MicroVision's early development work was financed by US government defense contracts and resulted in the prototype head-mounted display, Nomad.