The Stanford University School of Medicine has developed a retinal prosthesis similar to a solar cell system that can be surgically implanted under the retina to help restore vision to patients who are blind due to degenerative eye disease. Related papers were published in the "Nature · Photonics" magazine published today. In patients with retinal degenerative diseases such as age-related macular degeneration and retinitis pigmentosa, the retinal photoreceptor cells slowly degenerate, eventually leading to blindness, but the internal optic nerve is basically not damaged, and it can also transmit signals from the photoreceptor cells to the brain. Retinal prosthesis can help patients see the light again. The researchers said that their new retinal prosthesis device has a pair of specially designed eyepieces, which are equipped with a miniature camera and a microcomputer that processes visual data streams. The generated image is displayed on a miniature liquid crystal display embedded in the eyepiece. The near-infrared laser pulse projects the playback image on a photoelectric silicon chip, which is implanted under the retina and is only 1/3 as thin as a hair. The photodiode on the chip generates an electric current, causing the retinal signal to be transmitted to the brain, thereby allowing the patient to gain vision. "The working principle is like a solar cell, which converts light into electric current. The difference is that electric current is triggered in the retina." Daniel Palanke, one of the senior authors and associate professor of ophthalmology, said that the retina is like a film or digital chip. Each photosensitive cell is a pixel. They replaced these light-sensing cells with photodiodes. Each pixel is like a small solar cell. When exposed to light, it generates an electric current that stimulates the optic neurons in the inner layer of the retina. This creates a waterfall effect that activates ganglion cells in the outer layer of the retina and sends visual information to the brain so that patients can see it. There are other types of retinal prostheses currently in clinical trials, but the transplantation of these devices is cumbersome, and coils, cables, or antennas are implanted in the eyes to power and provide information to the implanted retina. The latest equipment uses near-infrared light to propagate images, does not require any wires or cables, and is very thin and easy to implant. "Surgery simply implants a small packet under the retina and puts a photovoltaic cell in it." Palanque said, and this photovoltaic cell can also be arranged in large numbers in the eye to provide a wider field of vision. In the experiment, the research team made a chip with the size of a pencil tip, containing hundreds of photodiodes, and used the retinas of normal mice and blind mice as models of degenerated retinas. They placed the chip under the retina and placed a multi-electrode array on the ganglion cell layer to detect current activity. After the light pulse is sent out, whether it is visible light or near infrared light, a current is generated in the photodiode. Normal mouse ganglia respond to visible light as expected, and respond similarly to near-infrared light. In the blind mouse's retina, normal light can only cause a weak response, and near infrared light triggers a strong response, almost reaching the level of the normal mouse retina. Preliminary experimental data shows that visual signals are reaching the brain, and the experiment is still in progress. Stanford University has applied for patents for two technologies in this system.
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