Age-related macular degeneration (AMD) is a common condition that affects the middle part of someone's vision, often worsening over time. Its exact cause is unknown, but occurs when light-sensitive photoreceptor cells and neurons in the center of the retina are damaged, making it hard to recognize faces or read. Approved treatments can only slow its progression.

People with advanced stage of geographic atrophy usually retain some photoreceptor cells that allow for peripheral vision and enough retinal neurons to pass visual information to the brain.

Taking advantage of this, Daniel Palanker at Stanford University in California and his colleagues have developed a device called PRIMA. It involves a small camera mounted on a pair of glasses that captures images, then projects them via infrared light to a 2 × 2 mm solar-powered, wireless chip implanted in the back of an eye.

The chip then converts this image information into an electric signal that retinal neurons can pass to the brain. Infrared light is used because we cannot see in this wavelength. The process doesn't interfere with any existing vision.

To test this, researchers recruited 32 people aged 60 or above who had geographic atrophy. Their vision in at least one eye was worse than 20/320, which means they could only see at 20 feet (6 meters) what a person with 20/20 vision could see at 320 feet.

The researchers first implanted this chip in one eye of these participants, then four to five weeks later, these volunteers began to use these glasses in their daily lives. The glasses allowed them to magnify what they were seeing 12 times and to adjust the brightness and contrast. After a year, 27 of these participants could read again as well as perceive shapes and patterns.

By giving participants this ability to perceive shapes and patterns, PRIMA represents the first prosthesis to restore functional sight in people with this condition.