The cathode ray tube (CRT) has been the primary active display device for the presentation of entertainment and information. Originally only in black-and-white, color CRTs are the standard today. There is much work to supplant the CRT with the lighter and smaller flat panel display which consist of liquid crystal (LCD), plasma and other technologies. All of these have the common principal that an image that is generated electronically is viewed with the optical system of the eye. The image you see is subject not only to the quality of the optical system of the eye, but also to the quality of the display and the environment in which the display is located.
What if you could bypass defects in the eye's optical system, such as damaged cornea and lens and reduced retinal sensitivity. What if you could remove the problems of the display environment, such as ambient brightness, angle-of-view and display brightness. What if you could naturally augment the image you see naturally with other information. This is the promise of a new display device called the Virtual Retinal Display or VRD for applications such as augmented reality for airplane pilots, an alternate display for computer images and the correction oflow vision (20/400) disorders.
Although the VRD is an input device, the technology lends itself to augmentation with eye tracking or eyegaze systems for output. Eye tracking is currently used in advanced still and video cameras for focusing on the object you wish to record. Coordinating augmented visuals from the VRD and real world scenes with eye tracking is an exciting input/output combination.
The VRD device rapidly scans low power, red, green, and blue lasers directly on the retina of the eye. Thus, it "paints" the image directly on the retina of the eye rather than the eye reading light from conventional displays such as the activated phosphors of a CRT or from light valves such as the LCD.
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This approach produces several advantages over conventional display devices:
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Potentially very small and lightweight, glasses mountable
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Large field and angle of view, greater than 120 degrees
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High resolution, approaching that of human vision
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Full color with better potential color resolution than conventional displays
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Brightness and contrast ratio sufficient for outdoor use
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True stereo 3D display with depth modulation
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Fully inclusive or see through
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Bypasses many of the eye's optical and retinal defects
The current prototypes being developed at the University of Washington's hit lab and at a small publicly listed company associated with the lab, Microvision, utilize components such as green argon ion and red diode lasers, acousto-optical modulators and a newer mechanical resonant scanner, fiber optic cable, y_galvo mirror collimators and beam splitters. The reason for this list is to show that, while the actual device to project the image onto the retina is small, the resulting generating, scanning, electronics and power supplies to generate the image is not. Even the portable version, modeled as a nice neat wearable pair of eyeglasses, is backed up by a substantial backpack with an AC cord to tether you to an electrical outlet. Current implementations are bulky and must be operated by engineers.
The connection to a support package, its size and the cost of the system relegate much of the current devices to military applications. The military applications abound from augmented low level night vision to weapons system cockpit displays. The see-through characteristics make it perfect for an augmented display superimposed over a real world image, since the normal field of vision of the real world can be unobstructed. Eye tracking and focusing devices, similar to those from Vision Control Systems, can be included to detect where the pilot is looking in the augmented image, similar in function to a touch screen on a flat display. For example, a combat pilot or soldier can track his/her target with the eye as the weapon's computer follows the eye's targeting. While viewing his/her approach speed in the VRD, a glance at the VRD displayed menu deploys the missile. The hands are free for other tasks. The eye continues to aid in guiding the missile to the target by continuous eye tracking.
Viewing of augmented information in 360 degrees adds the ultimate in viewability. The VRD is possibly the only display technology that has sufficient brightness to be used as an augmented display for viewing in bright sunlight such as aircraft cockpits and mechanized vehicles. The use of stereoscopic VRD's, promises to add even more realism to the augmented function and will ultimately lead to viewing the virtual 3D real world through such devices.
One promising application, other than military and entertainment, is as an aid for the partially blind or those with low vision disorders as severe as 20/400. Legal blindness in the United States is 20/200 vision. Possible causes are damage to the retina, central or peripheral field degradation, and damage to the optical pathway, corneal damage/malformation, or lens damage.
The VRD becomes a low vision aid by several mechanisms. First, the scanning beam has a very small exit pupil, which causes the beam to pass through only a small portion of the eye's optical path, avoiding defects. When the image reaches the eye it is about 30 degrees or wider. The small beam diameter creates a large depth of focus, making the projected image less sensitive to the optical aberrations of the eye. Second, the scanning beam has a very bright image and high contrast ratio across the full color scale. Third, the technique reduces glare from ambient light. Therefore, if the retina is impaired, these last two attributes can provide a much brighter and sharper image than other displays or natural conditions.
The VRD promises to aid the blind in reading printed material, watching television or computer screens, navigating inside and outside, and viewing real world scenes in near normal color and resolution.
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Entertainment and training simulators have great demand for enhancing the simulated environment of games and training exercises. By incorporated VRD technology into eyeglasses, goggles and helmets, these environments becomes more engaging through the use of stereoscopic 3D viewing. | ||
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The VRD is the only I/O device to date, capable of accomplishing almost all the principals of Learnability, Flexibility and Robustness. The ability to view naturally one's own real world, while three dimensionally augmenting and/or enhancing selected details with additional information, without the distracting effects of ambient brightness, impaired vision and limited view, is nothing short of fantastic. The only approach that can be taken beyond the VRD is direct connection to the optic nerve. That approach is experimental now and will mature in time. However, the VRD will be an important interim step that will take its rightful place in viewing technology.
Eye tracking devices for input add to this remarkable potential by offering hands-off control of computers and machinery. Automated capture of information through eye movements reduces task loading and increases the amount of data gathered. Other human facilities are left free for additional work. Eye movement becomes a previously untapped mode of communication. When coupled with the VRD, the system offers a major step toward one of the main tenets of ubiquitous computing initially described by Mark Weiser and his colleagues at Xerox PARC. That is, a less intrusive interface to the computer.
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