A virtual retina display (VRD) also known as a retinal scan (RSD) or retina (RP) screen, is a visualization technology that draws a raster display (such as a television) directly into the retina of the eye. The user sees what appears to be a conventional screen floating in the space in front of them.
In the past similar systems have been made by projecting an unfocused image directly in front of the user's eye into a small "screen", usually in the form of large crystals. The user focused his eyes on the background, where the screen seemed 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 to be focused only if the user was focusing on a "depth" particular,. The limited brightness made them useful only in the interior settings as well.
Only recently a number of developments have made a truly practical VRD system. In particular, the development of high-brightness LEDs has made the displays bright enough to be used during the day, and adaptive optics has enabled systems to dynamically correct irregularities in the eye (although this is not always necessary) . The result is a high resolution screen without screen with an excellent range of colours and brightness, much better than the best television technologies.
The VRD was invented by Kazuo Yoshinaka of Nippon Electric Co. in 1986. Subsequent work at the University of Washington at the Human Interface Technology Lab resulted in a similar system in 1991. Most of the research on VRDs to date has been in combination with several 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 type of optics to send the image into the eye, typically similar to the sunglasses system used with prior technologies. It can also be used as part of a portable computer system.
A Washington-based company, MicroVision, Inc., has tried to market VRD. Founded in 1993, MicroVision's early development work was funded by the US government's defense contracts and resulted in the prototype head-mounted display, Nomad.