The Virtual Retinal Display (VRD) constitutes an innovative technology to create images by scanning modulated laser light directly onto the retina of the viewer's eye. This method has been developed by Dr. Thomas A. Furness III in the Human Interface Technology (HIT) Laboratory at the University of Washington. In contrast with a conventional display, no real image is produced. Instead, a very small spot is focused onto the retina while scanned light beams are swept over it in a raster pattern. Despite the low power laser source, bright images with high contrast and resolution are generated to be readily seen in ambient room- and even daylight. Since the power levels recorded from the system remain way below those prescribed by the American National Standard, VRD reveals itself as a safe alternative for use in a surgical display and as an ideal visualisation technology for patients with low vision.
In January, the research team from the HIT Lab was invited to present the VRD visual display device at the "Medicine Meets Virtual Reality" Conference in San Diego. Indeed, the lightweight, full colour, and relatively inexpensive VRD system, with its wide field of view, is fit to be applied in graphical environments of virtual and augmented reality for visual interaction and immersion. For instance, a superimposed computer graphic with anatomic navigation information has to appear in an unobtrusive way during a surgical intervention but needs to be bright enough to be seen under the lights of the operating theatre. With VRD, the image colours match perfectly and correspond exactly to what the surgeon is seeing. These characteristic image features equally provide a useful help for people with partial loss of vision, allowing them to read text or watch television.
The VRD device actually consists of a polished mirror, placed on a mount. This Mechanical Resonance Scanner (MRS) is no larger than 2cm x 1cm x 1cm. The mirror oscillates in response to pulsed magnetic fields, produced by coils on the system mounting. From the moment that laser sources are introduced, the MRS mirror moves while the light is being scanned in the horizontal direction. Subsequently, the scanned light passes to a second MRS, scanning the light in the vertical direction, after which it is introduced to the eye. The illumination time lasts no longer than 40 nanoseconds. The VRD system has been tested by low vision subjects, in comparison with images on paper and on a computer screen. In general, these persons testified to experience equal or higher visual acuity with the VRD images, in any viewing condition, with or without glasses or contact lens correction.
The researchers believe that augmented vision and augmented reality will become one of the major applications of VRD technology. Further testing will have to elucidate the delicate interaction of VRD image perception with images out of the real world. Typically, in augmented vision, the images move with the subject's head whereas in augmented reality, the images are being held in registration with the real world, while the subject is moving. The VRD system generates true 3-D views, since it is able to project the image into both of the user's eyes from a slightly different view point, as to produce a stereo pair. The device can even vary the focus of each pixel within the image. You can find more details on the technical functioning of VRD and the safety analysis tests at the HIT Lab site of the University of Washington.