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A virtual retinal display (VRD), also known as a retinal scan display (RSD) or retinal projector (RP), is a display technology that draws a raster display (like a television) directly onto the retina of the eye. The user sees what appears to be a conventional display floating in space in front of them.
History
In the past similar systems have been made by projecting a defocused image directly in front of the user's eye on a small "screen", normally in the form of large glasses. The user focused their eyes on the background, where the screen appeared to be floating. The disadvantage of these systems was the limited area covered by the "screen", the high weight of the small televisions used to project the display, and the fact that the image would appear focused only if the user was focusing at a particular "depth". Limited brightness made them useful only in indoor settings as well.
Only recently a number of developments have made a true VRD system practical. In particular the development of high-brightness LEDs have made the displays bright enough to be used during the day, and adaptive optics have allowed systems to dynamically correct for irregularities in the eye (although this is not always needed). The result is a high-resolution screenless display with excellent color gamut and brightness, far better than the best television technologies.
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.