Prostheses for retinal stimulation

In a recent study published in Advanced Biomedical Engineering, researchers at Okayama University report a thin photoelectric film that can stimulate degenerated retinal tissue in the eye.

The use of electrical signals to stimulate tissue is the basis of several medical devices such as pacemakers for the heart or neurostimulators used in patients with epilepsy. A research team led by Dr. MATSUO toshihiko of the University of Okayama has developed OURePTM, a dye-coupled photoelectric thin film device that generates changes in electrical potential when exposed to light. In their latest study, the research team revealed the ability of this device to stimulate degenerate retinal tissue.

OURePTM is generated by placing polyethylene, a polymer, between two aluminum plates. When the polymer is melted and a high pressure is applied thereafter, a thin polyethylene film is created. The film then undergoes a chemical reaction in which it is coupled to a photoelectric dye.

The researchers first placed the photoelectric film coupled to a dye on the electrical potential measuring device and exposed it to a flashing light. As expected, electrical signal waves were observed on the surface of the film when light struck the film. In order to then test the ability of this film to stimulate nerve tissue, retinal tissues of rats with retinal dystrophy, a degenerative retinal disorder, were obtained. When retinal tissues from healthy rats were brought into close contact with a multiple electrode array, a device used to measure electrical signals from biological tissue and exposed to light, corresponding waves of electrical signals were observed. However, no such signal has been observed with dystrophic retinal tissue. The dye-coupled photoelectric film was then placed on the dystrophic tissues, which resulted in the induction of electrical signals in response to bursts of light. A control film, without the photoelectric dye, did not induce electrical signals in these tissues.

To more precisely measure these electrical signals, a nylon mesh has been used to maintain the dystrophic tissues and the multi-cell multi-cell array detector in close contact. This proximity revealed low amplitude electrical impulses with dystrophic retinal tissues alone. In the background of the low amplitude of these signals, light induced remarkable peaks of action potential in dystrophic retinal tissues, in the presence of the dye-coupled photoelectric film. The dye-coupled photoelectric film thus played a decisive role in stimulating electrical impulses in the degenerate retina.

"The present study provides direct evidence of the ability of dye-coupled photoelectric polyethylene film to induce an electroretinogram-like response and peaks of action potential in the degenerative retina," the researchers concluded. Retinitis pigmentosa is one of these conditions, characterized by the slow death of photoreceptors in the eye, leading to blindness. This study revealed the prosthetic value of OURePTM in the potential replacement of the lost photosensitivity of these cells. The implementation of the device and the visual improvement tests in animals in their previous studies have already brought additional information.