Virtual retinal display
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A virtual retinal display (VRD), also known as a retinal scan display (RSD), is a new 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.
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 sunglasses. 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 at the University of Washington in the Human Interface Technology Lab in 1991. Most of this 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 can be also used as part of a wearable computer system.
More recently, there has been some interest in VRDs as a display system for portable devices such as cell phones, PDAs and various media players. In this role the device would be placed in front of the user, perhaps on a desk, and aimed in the general direction of the eyes. The system would then detect the eye using facial scanning techniques and keep the image in place using motion compensation. In this role the VRD offers unique advantages, being able to replicate a full-sized monitor on a small device.
