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Inside Science and Technology 

In the Eye of the Beholder: Contact Lenses as Displays and Sensors 

11  2,009 

By Grace V. Jean 

The next time you look at a computer chip, imagine what might happen if the electronics were miniaturized and embedded into a contact lens. Scientists believe that the little plastic discs that hundreds of millions of people rely on to see clearer may one day serve military personnel and medical patients as information displays and health monitoring devices.

A research group at the University of Washington is developing “functional contact lens systems” that contain tiny sensors, radios, optoelectronic components and control circuits. The scientists are attempting to display computer-generated graphics on the lens without blocking the user’s field of vision and to measure the lens wearers’ biomarkers, or health indicators, in a non-invasive way.

“We’re making a lot of progress,” says electrical engineering professor Babak Parviz, the lead scientist for the research program.

Piggy-backing on advances made in the $2 trillion semiconductor industry, the team has fabricated prototype lenses using a technique developed in Parviz’s lab.

Traditional semiconductor fabrication processes employ high temperatures and corrosive gases to make components and embed them into substrates — a layer of silicon that is part of the wafer. The heat and chemicals are hostile to unconventional substrates made from flexible polymers — in this case, a plastic similar to the material found in hard contact lenses.

Because manufacturing the components directly onto a lens is impossible, the new process involves fabricating the subcomponents separately onto silicon-on-insulator wafers and other substrates first, and then employing a chemical process to allow the subsystems to self-assemble and implant themselves into the contact lens.  

To the naked eye, these subcomponent devices — the miniscule biosensors, antennae, semiconductor circuit components and micron-scale light sources — collectively resemble a fine white powder. But each component is etched into different shapes to match its place on the contact lens system with metal interconnects. The team submerges the flexible transparent polymer substrate in a chemical liquid medium. As the components flow by, they fall into place like pieces of a puzzle. Alloys at the bottom of these “slots” lock them in.  

Using this process, the team has fabricated contact lenses with light-emitting diodes, radio chips and antennae. “We have been able to show that we can beam in radio frequency and operate the light source,” says Parviz. Transmitting the microwatts of energy via radio frequency waves to an antenna on the contact lens has proved to be a safer and more power-efficient alternative than using batteries, he says.  

The team also has built sensors that detect the concentration of a molecule, such as glucose, in the biomarkers found in the live cells on the surface of the eye. Concentration levels in the eye are comparable to those found in the bloodstream. Diabetics could wear the lenses and avoid needle pricks to test their blood glucose levels, says Parviz, who is eager to interface the contact lens system with a mobile device worn on the body. If the contact lens samples blood glucose and cholesterol levels, for example, then it could transmit the information to a cell phone or PDA, which would relay that data to medical facilities.

Safety tests of the lens prototypes are being conducted in animal trials. Because human tests are not yet feasible, the team has modeled the optical design of the display system on a computer to show how the world would appear through the lens.

When worn, users will be able to see through the lenses normally. But if they want to view computer-generated images or text from a PDA, the lenses can superimpose the information over the person’s field of view.

At an Institute for Defense and Government Advancement night vision conference, Parviz puts up a slide depicting a simulation that illustrates how a 7-by-7 grid of LEDs, distributed over a square 25 microns across, would display text. In the still shot, a slightly unfocused letter “F” glows, layered over a nighttime urban street corner scene.

“No one has ever created an image that you can see by placing [a lens display] on your eye directly. This is the first time ever of doing that,” says Parviz. But the team has yet to demonstrate it in practice, he points out.

Work progresses on the display system’s optical design to form the sharpest images possible. “Our goal is to increase the pixel count and eventually introduce color,” says Parviz.

As the lab continues to produce prototypes, it also is working to increase the range of the radio, reduce the overall power consumption of the system and fabricate the components onto soft contact lens material.

“My definite hope is that in the coming decade we will see some of these devices out and working,” he says.
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