Soft multi-electrode ERG system

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 a multi-electrode ERG system built on top of commercial soft contact lenses with the hope of improving diagnostic techniques for the early detection and monitoring of ocular diseases.

Among the arsenal of tools ophthalmologists have at their disposal, ERG still holds much-untapped potential. 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.

Against this background, a research team led by Professor Takeo Miyake from 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. Their latest study, published in Advanced Materials Technologies, describes their findings. It was co-authored by Saman Azhari from the Graduate School of Information, Production, and Systems at Waseda University, as well as Atsushige Ashimori and Kazuhiro Kimura from the Department of Ophthalmology at Yamaguchi University.

The proposed system uses a commercially available soft disposable contact lens. Researchers first immersed the contact lens in a solution containing the monomer 3,4-ethylenedioxythiophene (EDOT). Next, designed gold mesh electrodes with their respective connecting wires were placed on 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.

A key advantage of this approach is the PEDOT layer can be overoxidized 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 don’t 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 the overoxidation process, the PEDOT encapsulating the mesh region doesn’t overoxidize, ensuring good electrical contact with the eye.

The result of this process is a flexible and highly transparent multi-electrode system for ERG measurements that’s just as comfortable as commercial disposable contact lenses. The researchers carefully examined the optoelectrical properties of their multi-electrodes and conducted some experiments on rabbits.

“Our device was used in animal experiments, confirming its biocompatibility and suggesting a correlation between the location of the electrodes and the intensity of the recorded ERG signals,” Miyake says. “The use of augmented and virtual reality devices is growing quickly, and the precise and continuous monitoring of eye conditions will become a necessity. 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’s performing their daily routine. Such systems could prevent irreparable damage to the eyes.”