Tiny PV cells in artificial retina act as image-to-current converters

Artificial retinas hold promise for improved vision for patients whose eyes’ photoreceptors have degraded due to conditions such as retinitis pigmentosa. Here’s a NYTimes article on the development of artificial retinas that explains how they work and points out one of their challenges: Getting enough electrodes implanted in the back of the eye to allow some useful amount of vision. The eye naturally has many, many photoreceptors. Not only is space limited for implanted electrodes, but powering them in an additional challenge.

Here’s a photo of an artificial retina system that shows the glasses-mounted camera.

“The device, known as the Argus, is simple in concept: The camera, mounted to a pair of glasses, picks up images and wirelessly beams them to a receiver implanted near the eye. The receiver sends data to an electrode array tacked inside the eyeball. The electrodes stimulate receptor cells in the retina, which signal the visual processing centers of the brain, which translate the signal into the experience of sight. Making all this happen is quite complicated, requiring careful attention to everything from the frequency of the wireless signal to the heat generated by the electrode patch.”

Researchers at Stanford have come up with a clever solution: Use tiny solar cells in place of the electrodes. A glasses-mounted IR camera sends images to an LCD (also on the glasses) that’s bright enough to illuminate the implanted sensor and produce electricity in its tiny photovoltaic cells. The current stimulates the eye in much the same way that the eye’s own  photoreceptors work.

The implant is made with a MEMs process. Below is a close-up view of the flexible retinal implant made of silicon. It has tiny bridges that allow it to fold over the shape of the eye and provide a high-resolution image. 

Via IEEE Spectrum.

And here’s an article from last month about research at Sandia National Labs into glitter-sized solar cells made with their MEMs process. These PV cells are referred to as “several hundreds of microns” in diameter.