Study: Taking electroretinography to the next level with soft multi-electrode system

(Image Credit: AdobeStock/Crazy Juke)

Amid an aging population and an increase in screen time compared to previous generations, eye diseases are on the rise worldwide. With the use of myriad displays expected to continue to increase with the rise of technologies such as virtual and augmented reality, ophthalmologists must improve diagnostic techniques for the early detection and monitoring of ocular diseases.

The toolbox ophthalmologists rely on includes electroretinography (ERG), which still holds untapped potential. According to a Waseda University news release, it 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.¹

While there are a number of ERG measurement devices available, 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 expensive, complex, and particularly uncomfortable for the patient. 

As a result, the research team, led by Takeo Miyake, PhD, 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.

The researchers’ latest study was published in May, 2024, in Advanced Materials Technologies, outlining their results.² The study was co-authored by Saman Azhari, PhD, MSc, 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.²

The system proposed by the researchers 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.

A key advantage of this approach is that the PEDOT layer can be overoxidized by using a DC voltage under dry conditions, 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 the overoxidation process, the PEDOT encapsulating the mesh region does not overoxidize, thus ensuring good electrical contact with the eye.

The process results in a flexible and highly transparent multi-electrode system for ERG measurements that is just as comfortable as commercial disposable contact lenses. The researchers examined the optoelectrical properties of their multi-electrodes and also conducted some experiments on rabbits.²

“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 said in the news release. “In other words, our design could enable precise spatial measurements of multiple ERG signals simultaneously.”

According to the researchers, the results of the study may help researchers to better understand and diagnose ocular diseases.

The researchers noted in the study the ME_ERG recording in rabbits demonstrated that the ERG signals were higher in the central region of the periphery, offering the opportunity to study the spatial variations in ERG responses, which could ultimately help detect and diagnose diseases impacting specific areas of the eye.

“The use of augmented and virtual reality devices is growing quickly, and the precise and continuous monitoring of eye conditions will become a necessity,” Miyake concluded. “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.”

References:

1. Taking electroretinography to the next level with a soft multi-electrode system. EurekAlert! Accessed May 29, 2024. https://www.eurekalert.org/news-releases/1044221

2. L. Hu, S. Azhari, Q. Li, H. Zhang, A. Ashimori, K. Kimura, T. Miyake, Multi-Electrode Electroretinography with Transparent Microelectrodes Printed on a Soft and Wet Contact Lens. Adv. Mater. Technol.2024, 2400075. https://doi.org/10.1002/admt.202400075