Smart Contact Lenses

Scientists at the University of California, Davis, have recently designed a contact lens prototype with a built-in pressure sensor using a novel process that etches tiny electrical circuits within a soft polymer material. The new development could help glaucoma patients to measure their current risk factor, thus replacing the current methods which require the constant visit of a clinician.


 	These contact lenses with a pattern of conductive silver wires could be used to measure pressure inside the eye and study glaucoma, a major cause of blindness. (Tingrui Pan/UC Davis photo)
These contact lenses with a pattern
of conductive silver wires could be used to
measure pressure inside the eye and study
glaucoma, a major cause of blindness.
(Credit: Tingrui Pan/UC Davis photo)

The lens’s designer, Tingrui Pan, assistant professor of biomedical engineering, says that the design may eventually be fashioned into disposable contact lenses, enabling patients to continuously monitor glaucoma at home. Currently the only way for patients with glaucoma to keep tabs on the disease is by visiting a clinician or a doctor who administers one of several tests to measure glaucoma’s main risk factor, intraocular pressure (IOP). However, these visits occur usually two or three times a year, and there is no way to monitor pressure spikes between visits.

In glaucoma, drainage of the fluid that normally delivers nutrients to and removes metabolic waste from the eye is blocked. Elevated pressure in the eye ultimately presses on the retina, compromising neural activity and damaging the optic nerve, resulting in loss of vision. Current treatments of glaucoma include the measurement of patients’ IOP and prescription of drugs to lower it. James Brandt, a professor of ophthalmology at UC Davis and Pan’s collaborator, explained the complexity involved: “It’s very different from situations like cardiac disease or diabetes, where patients can wear devices that measure heart rate or blood pressure 24 hours a day for a week or more to get a better idea of what’s going on; we don’t have that for glaucoma, and that’s one of the biggest clinical frustrations we have.”

Wireless implantable micro-nanosystems (Credit: UC Davis)
Wireless implantable
micro-nanosystems (Credit: UC Davis)

Pan’s team recently made a contact-lens prototype from PDMS, an organic polymer commonly used to make contact lenses and breast implants. “This material has been widely used in biology because it’s easy to work with and can bend and flex like skin,” says Pan. “But the problem is, it’s not conductive, and if you want to make it sensing, it has to be conductive.” Because it’s difficult for metal wires to adhere directly to the polymer’s surface, Pan looked for creative ways to embed metal within the polymer. By creating a mixture with a chemical agent the researchers managed to make the polymer sensitive to ultraviolet (UV) light. The result was that when exposed to UV light it solidified, forming a soft, rubber-like material and without UV light the polymer remained in its liquid form.

The next step was the creation of a negative cutout in the pattern of a small circuit. UV light was shone through the cutout onto a layer of a polymer mixture. As expected, areas exposed to light gelled while those under the cutout did not. Thus, researchers were able to easily wash away the liquid polymer leaving an imprint of a small nanoscale circuit within the solidified polymer. Afterwards Pan filled the pattern with a solution of powdered silver, which is a nontoxic metal conductor. After polymerization, the silver formed a continuous circuit within the soft polymer.

During initial laboratory tests it was found that the voltage within the tiny circuit changed slightly as the polymer bent. Using this technique the change is measured and according to Pan it could be a good indicator for IOP since when pressure within the eye increases the shape of the contact lens will distort, causing a change in voltage within the wires. “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.”

Although the prototype seems promising, several hurdles remain before it can be practically used as a 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, but nevertheless he looks for materials that could be made into transparent circuits for longer-term use.

TFOT has also covered the new bionic eye that could restore sight, developed at the Boston Retinal Implant Project, and the SIAFU, a computer designed for the blind by industrial designer Jonathan Lucas. TFOT also features an extensive article entitled “Shedding Light on Blindness,” written by Gadi Howard.

More information on the new smart contact lenses can be found on UC Davis’s website.

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