Soft electrodes for smart contact lenses
Researchers in Japan have developed a multi-electrode system built on top of commercial soft contact lenses for detecting eye diseases.
The proposed smart contact lens can measure electrical potentials from different places in the retina simultaneously, which is useful in diagnosing a wide range of conditions.
Electroretinography (ERG), which involves measuring electric potential in the retina, is a powerful tool for diagnosing and studying ocular diseases. However, multi-electrode systems for ERG are usually built on top of hard, uncomfortable contact lenses. To address this issue, researchers from Japan developed an innovative
Image caption: Electrical potentials measured on the retina hold important information that can help diagnose diseases of the eye, including glaucoma and retinitis pigmentosa, early on. In this study, researchers developed a multi-electrode system built on top of commercial disposable contact lenses for making such measurements conveniently.
Eye diseases are becoming more prevalent worldwide, partly because of the aging population, but also because of the greatly increased screen time compared to previous generations. Considering the use of displays will most likely keep rising due to technologies such as virtual and augmented reality, diagnostic techniques for the early detection and monitoring of ocular diseases needs to improve.
ERG consists of taking measurements of the electrical potentials generated by neurons and other cells in the retina from the surface of the cornea. Many ocular diseases cause abnormalities in a person’s ERG signals, including glaucoma, retinitis pigmentosa, and diabetic retinopathy. Although many types of ERG measurement devices exist, few ERG electrodes can measure multiple localized ERG signals from different regions of the retina at the same time. In most cases, such measurements are performed using electrodes placed on hard contact lenses. This makes the procedure more complex, expensive, and particularly uncomfortable for the patient.
The researchers at the Graduate School of Information, Production and Systems at Waseda University, Japan, set out to develop a new type of soft ERG multi-electrode system to overcome these issues.
The proposed system uses a commercially available soft disposable contact lens. The researchers first immersed this contact lens in a solution containing the monomer 3,4-ethylenedioxythiophene (EDOT). They then placed carefully designed gold mesh electrodes with their respective connecting wires onto the inner surface of the contact lens. By circulating a current through the solution containing EDOT, the monomers formed an entangled polymer called PEDOT, which adhered well to the contact lens and fixated the gold components.
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A key advantage of this approach is that the PEDOT layer can be overoxidized by using a DC voltage under dry condition, thereby forming a highly insulating layer on the collecting wire. This insulation is critical to ensure different retinal signals flowing through the gold wires do not interfere with one another or with signals originating from other regions of the eye. By carefully designing the gold mesh of the electrodes to spread currents during overoxidation process, the PEDOT encapsulating the mesh region does not overoxidize, thus ensuring good electrical contact with the eye.
The result is a flexible and highly transparent multi-electrode system for ERG measurements that is just as comfortable as commercial disposable contact lenses. The researchers carefully examined the optoelectrical properties of their multi-electrode smart contact lens system.
“The use of augmented and virtual reality devices is growing quickly, and the precise and continuous monitoring of eye conditions will become a necessity,” said Prof Takeo Miyake who led the research. “A smart contact lens such as the one developed in this work could be connected to a local network to transmit the eye’s health condition to an ophthalmologist or healthcare specialist while the user is performing their daily routine. Such systems could prevent irreparable damage to the eyes.”
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