Contact lenses for health and head-up displays

Lenses that monitor eye health are on the way, and in-eye 3D image displays are being developed too – welcome to the world of augmented vision

THE next time you gaze deep into someone's eyes, you might be shocked at what you see: tiny circuits ringing their irises, their pupils dancing with pinpricks of light. These smart contact lenses aren't intended to improve vision. Instead, they will monitor blood sugar levels in people with diabetes or look for signs of glaucoma.

The lenses could also map images directly onto the field of view, creating head-up displays for the ultimate augmented reality experience, without wearing glasses or a headset. To produce such lenses, researchers are merging transparent, eye-friendly materials with microelectronics.

In 2008, as a proof of concept, Babak Parviz at the University of Washington in Seattle created a prototype contact lens containing a single red LED. Using the same technology, he has now created a lens capable of monitoring glucose levels in people with diabetes.

It works because glucose levels in tear fluid correspond directly to those found in the blood, making continuous measurement possible without the need for thumb pricks, he says. Parviz's design calls for the contact lens to send this information wirelessly to a portable device worn by diabetics, allowing them to manage their diet and medication more accurately.

Lenses that also contain arrays of tiny LEDs may allow this or other types of digital information to be displayed directly to the wearer through the lens. This kind of augmented reality has already taken off in cellphones, with countless software apps superimposing digital data onto images of our surroundings, effectively blending the physical and online worlds.

Making it work on a contact lens won't be easy, but the technology has begun to take shape. Last September, Sensimed, a Swiss spin-off from the Swiss Federal Institute of Technology in Lausanne, launched the very first commercial smart contact lens, designed to improve treatment for people with glaucoma.

The disease puts pressure on the optic nerve through fluid build-up, and can irreversibly damage vision if not properly treated. Highly sensitive platinum strain gauges embedded in Sensimed's Triggerfish lens record changes in the curvature of the cornea, which correspond directly to the pressure inside the eye, says CEO Jean-Marc Wismer. The lens transmits this information wirelessly at regular intervals to a portable recording device worn by the patient, he says.

Like an RFID tag or London's Oyster travel cards, the lens gets its power from a nearby loop antenna - in this case taped to the patient's face. The powered antenna transmits electricity to the contact lens, which is used to interrogate the sensors, process the signals and transmit the readings back.

Each disposable contact lens is designed to be worn just once for 24 hours, and the patient repeats the process once or twice a year. This allows researchers to look for peaks in eye pressure which vary from patient to patient during the course of a day. This information is then used to schedule the timings of medication.

"The timing of these drugs is important," Wisner says.

Parviz, however, has taken a different approach. His glucose sensor uses sets of electrodes to run tiny currents through the tear fluid and measures them to detect very small quantities of dissolved sugar. These electrodes, along with a computer chip that contains a radio frequency antenna, are fabricated on a flat substrate made of polyethylene terephthalate (PET), a transparent polymer commonly found in plastic bottles. This is then moulded into the shape of a contact lens to fit the eye.

Parviz plans to use a higher-powered antenna to get a better range, allowing patients to carry a single external device in their breast pocket or on their belt. Preliminary tests show that his sensors can accurately detect even very low glucose levels. Parvis is due to present his results later this month at the IEEE MEMS 2011 conference in Cancún, Mexico.

"There's still a lot more testing we have to do," says Parviz. In the meantime, his lab has made progress with contact lens displays. They have developed both red and blue miniature LEDs - leaving only green for full colour - and have separately built lenses with 3D optics that resemble the head-up visors used to view movies in 3D.

Parviz has yet to combine both the optics and the LEDs in the same contact lens, but he is confident that even images so close to the eye can be brought into focus. "You won't necessarily have to shift your focus to see the image generated by the contact lens," says Parviz. It will just appear in front of you, he says. The LEDs will be arranged in a grid pattern, and should not interfere with normal vision when the display is off.

For Sensimed, the circuitry is entirely around the edge of the lens (see photo). However, both have yet to address the fact that wearing these lenses might make you look like the robots in the Terminator movies. False irises could eventually solve this problem, says Parviz. "But that's not something at the top of our priority list," he says.