November 23, 2011 | 4
Over past 125 years, contact lenses have come a long way. What started off as relatively thick brown glass eye coverings first created by German ophthalmologist Adolf Fick has evolved into biosensor-laden polymer lenses that can measure eye movement, glucose concentrations in tears and intraocular pressure. Now a team of researchers is investigating whether the integration of light-emitting diodes (LEDs), circuitry and antennas into modified contact lenses can transform them into miniature augmented reality displays.
University of Washington associate electrical engineering professor Babak Parviz and his colleagues are starting off modestly. In the Institute of Physics Publishing’s Journal of Micromechanics and Microengineering on Tuesday (pdf), they report having developed a contact lens that when worn can display a single pixel to the wearer. The ultimate goal is to create a multipixel display that would let the wearer view digital text and images over his or her view of the physical world without so much as batting an eyelash.
For instance, if you were touring New York City with the help of a mobile app that labeled different landmarks, when you looked at the Statue of Liberty, the words “Statue of Liberty” might appear to float in the air between you and the statue. Video-game companies might use the contact lenses to immerse players in a virtual world without the need for bulky goggles or even eyeglasses. Lens wearers might also be able to surf the Internet on a virtual display screen that only they would be able to see, according to the researchers.
Parviz and his team first reported their ability to imprint electronic circuits and lights onto contact lenses in January 2008 at the Institute of Electrical and Electronics Engineers’ international conference on Micro Electro Mechanical Systems. At the time, their goal was to demonstrate that such lenses could be worn safely, which they did by placing the lenses on the eyes of lab rabbits.
The newest version of the lenses includes antennas to harvest power sent out by an external source (such as a cell phone), as well as integrated circuits to store this energy and transfer it to an LED light source, which would illuminate images on the lens. “Up to this stage, we’ve made a lot of contact lenses, but none of them have been actually tested for operation on a live eye,” says Parviz, who adds that much of the work developing the lens’s semiconductor was done in conjunction with researchers at Finland’s Aalto University. “This is the first time that we turned them on and demonstrated that they work and were safe for at least short periods of time.”
Building such lenses is a challenge for several reasons. The manufacture of electrical circuits typically involves inorganic materials, high temperatures and toxic chemicals—none of which are conducive to eye safety. To address this challenge, the researchers built the circuits using a minimum of materials, including layers of metal only a few nanometers thick—about one-thousandth the width of a human hair—and constructed tiny light-emitting diodes one-third of a millimeter across.
Another key part of the research was testing whether they could project an image onto the lens in such a way that the eye could see it. Because the human eye normally is unable to focus on anything closer than 15 centimeters, Parviz and his team compensated for the problem by incorporating a miniature Fresnel lens into their contact lenses. Fresnel lenses—originally designed for lighthouses—are flat and thin, and allow for a large aperture and a short focal length. “If an image is placed on a Fresnel contact lens, I can force the light rays to converge on the retina, making the light source more in focus,” Parviz says. “In a sense the lens tricks the eye into thinking that the image is farther away so it can focus on it.”
Other challenges include shrinking the size of the LED so that the researchers can increase the pixel count while keeping the system low power so its circuits can operate using radio waves or light rather than a battery. Batteries are notoriously inefficient and generally are made from toxic substances you wouldn’t want near your eyes. Given the eye’s sensitivity, there is also a cap on the amount of energy that the contact lenses can produce without damaging the cornea. “We’d like to limit the power to a few microwatts because there’s not really a good way to remove heat from the surface of the eye,” Parviz says.
Obviously it’s going to take a lot more work before we have the computer-enhanced cyborg vision in the Terminator movies, but you never know what could happen in the next 18 years—the future portrayed in those films is 2029.
“Eventually our plan is to have full-fledged display with reasonable resolution and color that can receive images from an external device and superimpose those images over what you would normally see,” Parviz says. “We are very far from that but are taking small steps in that direction.”
Image courtesy of the University of Washington in Seattle