Tuesday, August 05, 2008

Pressure-Sensing Contact Lenses

Continued from page 1

By Jennifer Chu

Pan filled the pattern with a solution of powdered silver, a nontoxic metal conductor. After polymerization, the silver formed a continuous circuit within the soft polymer. In initial laboratory tests, the team found that voltage within the tiny circuit changes slightly as the polymer is bent. Pan says that measuring this change could provide a good monitor for IOP: as pressure within the eye increases, the shape of the contact lens would distort, causing a change in voltage within the wires. The researchers published their results in the recent issue of the journal Advanced Functional Materials.

"This device is really a breakthrough in real-time IOP monitoring," says David Calkins, associate professor of ophthalmology at Vanderbilt University Medical Center, who was not involved in the research. "We don't have a means right now to measure pressure in real time outside of the clinic. Because of that, we are missing the fluctuations in IOP that could be pertinent to the pathogenesis of glaucoma."

However, several hurdles remain before the prototype can be fashioned into a practical contact lens. In the current version, the silver circuit is opaque and would obviously obstruct vision. Pan says that such a visible circuit could still be used for short-term, sit-down tests in the clinic. However, he is also looking for materials that may be made into transparent circuits, for longer-term use.

Powering the lens also presents a problem. Ideally, Brandt says, a "smart" contact lens would consist of an electrical pressure sensor as well as an RFID tag to wirelessly transmit information to a computer, along with a small battery to power the device. "Getting energy to the device, and pulling information off of it, is not a trivial task," he says.