Most of us will experience some form of vision impairment at some point in our lives…whether it’s simple myopia, age-related macular degeneration, injury or disease, vision correction will be necessary for most. For many, however, visual impairment is more severe. The American Foundation for the Blind states that 8 million Americans are blind. Approximately 15 percent of this population is totally sightless. The other 85 percent have some limited sight but is almost as debilitating as total blindness. This condition is known as legal blindness or low vision.
The engineering challenge was how to best electronically optimize the minimal usable vision that exists with people with low vision so that they can participate in everyday activities the fully sighted take for granted: reading, watching TV, working, cooking and independently travelling by foot, taxi, public transit or planes.
A Canadian company, eSight Corporation, has met this engineering challenge by developing a novel, high-tech approach that enhances visual acuity for people coping with a variety of low vision conditions including macular degeneration, diabetic retinopathy, ocular albinism, cone-rod dystrophy, Stargardt’s disease and some cases of retinitis pigmentosa.
How the eSight system worksThe first generation of the eSight Eyewear system (G1) consists of a head-mounted camera and display unit that is connected by cable to a controller, data processing unit and battery pack which is worn on a belt or placed in a customized over-the-shoulder pouch. The head-mounted display sends images from a specialized video camera to the controller where the images are processed. The controller transmits imagery back to the display where it is presented by two organic LED micro-displays and an optical prism system. The engineers at eSight have managed to address latency issues and deliver a 30 frames/second refresh rate by taking advantage of parallel processing and custom software.
A unique patented feature of the eSight headgear is that it is bioptic – it can be tilted down to provide a close-to-immersive field of view or tilted up to allow an eSight user to optimize peripheral vision for visual reference and orientation.
The video camera is a key element in the system. It’s composed of a lens, focus motor, five megapixel image sensor and rangefinder. The rangefinder feeds distance information to the data unit. The data unit in turn drives the focus motor, allowing sharp, high contrast image capture in real time (<100 milliseconds).
eSight offers a much wider field of view compared to a system using a simple magnifier. eSight eyewear can also integrate a user's eyeglass prescription, if one exits, and present images through its specialized optics at optical infinity. The system allows digital television and computer monitor inputs with zoom and inertial sensor-based panning of these inputs for direct viewing.
The eSight user can use the controller to enhance the video image with zoom (1.5 – 14 x), contrast, brightness and reverse color displays. The controller even allows the user to freeze a frame, for reading or to save the picture onto an integrated micro disk.
The data processing unit uses several image processing strategies to convert and process raw camera data, including contrast histogram stretch, edge enhancement and image binarization using Otsu’s Method to automatically optimize binary images. Code is written in ‘C’ and allows Internet-based upgrades, maintenance and support. The Web connectivity suggests possible future applications of the technology in immersive environments similar to Oculus Rift or for data-enhanced vision like Google Glass.
The display uses a pair of 0.5-inch OLED micro-displays coupled to wide field prisms (both supplied by eMagin), offering a sharp 800x 600 image with tolerance of differing user’s pupil distances.
Vision systems: a technical balancing act
Helmet-mounted targeting and low light optics have existed for decades in the military, but advanced technology for the low-vision market is new. From an engineering perspective, there is a significant difference between military optics, dedicated low-vision technologies, and gaming/Bluetooth devices.
Military systems are highly developed, but are designed to be helmet mounted. Helmet mounting greatly reduces the weight constraint imposed by visor-type systems. Military systems are also single-purpose devices: software and optics are optimized for ordinance delivery, not the broad range of colours and contrasts handled by human eyes every day.
At the other extreme are Internet/gaming systems. While their lighter weight makes them useful for people who aren’t wearing helmets, they are designed to be worn by users with normal vision. As a result, gaming systems are optimized to deliver information without the challenge of accurate, real-world rendition of light, contrast and colour.
The cost issue is similarly polarized. Six-figure imaging systems are tolerable in multimillion dollar military aircraft, while gaming systems require two or three-digit pricing for mass appeal. The challenge for firms like eSight who are engineering for the low-vision community is not only technical - it’s keeping the price point at a level accessible to a majority of potential users.
This problem is exacerbated by the need to place the displays close to the eye for an ideal wearer experience. The current state-of-the-art in near-to-eye display technologies forces several crucial performance/design trade-offs in the field of view, image quality [acuity and sharpness] distortion, brightness, chromatic dispersion, volume and weight among others.
Additional design challenges are driven by the remarkable image processing speed of the human brain. A recent MIT study published in the journal Attention, Perception and Psychcophysics has shown image processing speeds that let the human brain perceive images in as little as 13 milliseconds. For a machine system to keep up, focus control must be lag free. The requirement to zoom introduces additional design constraints. Zoom affects not only the field of view, but also the effective aperture of the camera. This poses challenges to quickly correcting color and white balance must.
The fact that the system is worn on a person’s head introduces additional design challenges, such as image stabilization and light sensitivity, especially as the wearer transitions from low to high light environments.
Users of digital cameras understand that image quality is about more than just megapixels. A great image requires optics with enough light gathering ability and focus control to present a quality image to the sensor, which itself must have adequate light sensitivity and minimal pixel size. Current consumer devices such as Google Glass, Epson Movario and Sony’s HMZ – T3 lack either image quality or the built-in camera system necessary for a true low-vision assistive device.
A class by itself
The eSight system is fundamentally different from both consumer market devices and current low-vision assistive technologies. Common low vision aids are desktop readers and handheld electronic magnifiers. eSight is not the first electronic head mounted devices to be tested. The Jordy (Enhanced Vision Systems, Huntington California) and the LV 920 Sightmate (Vuzix, Rochester, NY) came earlier. Both those products, no longer available on the market, used lower quality LCD displays, lower resolution cameras, simpler analog image processing, and a fully immersive headset as opposed to eSight’s bioptic capability which is of critical importance for an individual with low vision to leverage whatever peripheral vision might exist.
eSight is continuing research and development efforts to increase functionality and reduce cost and size. Minor software revisions are planned on a 4 to 8 week cycle, with major releases planned every six months. New generation product releases are planned on an 18 month cycle. eSight regards the current technology as a “Generation One” product, and has begun G2 development with a target of fall 2015 availability. In the medium-term, the company plans to leverage advanced smart phone technology for a G3 product planned for the spring of 2016.
eSight Eyewear was conceived and initially funded by Conrad Lewis, formerly CTO at Newbridge Networks (now Alcatel). Conrad was motivated to help his two sisters who are legally blind due to Stargardts Disease, a condition that degrades the macula. With a very large global community of potential low-vision users and an aggressive product development plan, combined with high performance sensing and data processing technologies, eSight Corporation is creating a new class of assistive device with the potential to help millions worldwide.