For years, they had been losing their central vision—what allows people to see letters, faces, and details clearly. The light-receiving cells in their eyes were deteriorating, gradually blurring their sight.

But after receiving an experimental eye implant as part of a clinical trial, some study participants can now see well enough to read from a book, play cards, and fill in a crossword puzzle despite being legally blind. Science Corporation, the California-based brain-computer interface company developing the implant, announced the preliminary results this week.

When Max Hodak, Science’s CEO and former president of Neuralink, first saw a video of a blind patient reading while using the implant, he was stunned. It led his company, which he founded in 2021 after leaving Neuralink, to acquire the technology from Pixium Vision earlier this year.

“I don’t think anybody in the field has seen videos like that before,” he says.

Dubbed the Prima, the implant consists of a two-millimeter square chip that is surgically placed under the retina, the backmost part of the eye, in an 80-minute procedure. A pair of glasses with a camera captures visual information and beams patterns of infrared light on the chip, which has 378 light-powered pixels.. Acting like a tiny solar panel, the chip converts light to a pattern of electrical stimulation and sends those electrical pulses to the brain. The brain then interprets those signals as images, mimicking the process of natural vision.

There have been other attempts to restore vision by electrically stimulating the retina. Those devices have been able to produce spots of light called phosphenes in people’s field of sight—like blips on a radar screen. They’re enough to help people perceive people and objects as whitish dots, but it’s far from natural vision.

One of these, called the Argus II, was approved for commercial use in Europe in 2011 and in the US in 2013. That implant involved larger electrodes that were placed on top of the retina. Its manufacturer, Second Sight, stopped producing the device in 2020 due to financial difficulties. Neuralink and some others, meanwhile, are aiming to bypass the eye completely and stimulate the brain’s visual cortex instead.

Hodak says the Prima differs from other retinal implants in its ability to provide “form vision,” or the perception of shapes, patterns, and other visual elements of objects. What users see isn’t “normal” vision though. For one, they don’t see in color. Rather, they see a processed image with a yellowish tint.

The trial enrolled people with geographic atrophy, an advanced form of age-related macular degeneration, or AMD, that causes gradual loss of central vision. People with the condition still have peripheral vision but have blind spots in their central vision, making it difficult to read, recognize faces, or see in low light.

In AMD, specialized cells called photoreceptors are damaged over time. Located at the back of the retina, photoreceptors convert light into signals that are sent to the brain. “The photoreceptors are lost but the retina is preserved to a large extent. In our approach, the implant takes the place of the photoreceptors,” says Daniel Palanker, a professor of ophthalmology at Stanford University, who invented the Prima implant.

The trial enrolled an initial 38 participants ages 60 and older in the UK and Europe, but six people dropped out of the study before the one-year mark. To measure improvement in vision acuity—the clarity or sharpness of vision—researchers used a classic eye chart. The volunteers started off with an average visual acuity of 20/450. Normal visual acuity is considered to be 20/20, and in the US, legal blindness is defined as 20/200 or worse.

After a year, the 32 people who stayed in the trial were able read nearly five more lines down the vision chart, or 23 letters, on average compared to what they could at the start of the study. It was enough to improve their eyesight to an average of 20/160. Palanker says some participants are even able to see at 20/63 acuity using the implant’s built-in zoom and magnification feature. While most of the participants saw a notable improvement after a year, five didn’t see a benefit at all.

“The results are very impressive,” says James Weiland, a biomedical engineer and ophthalmologist at the University of Michigan, who wasn’t involved in the study. He notes, though, that the preliminary data doesn’t include whether the participants were using the zoom feature while doing the vision tasks in the trial. He says that matters because turning on the zoom function is something a user has to do manually, making the process of seeing with the implant less natural.

“It’s a step forward for retinal prostheses, for sure. But there are some details we don’t know that could tell us how big of a step it is,” Weiland says. “And one of those details is whether the patients were using a magnified image when they recognized these letters.”

A spokesperson for Science Corporation says participants have the option to use the zoom feature as needed but didn’t provide details on how often it was used during the study period.

“Of the various chip implant technologies that have been tried over time, this is the one that seems like it has some legs to it,” says Sunir Garg, an ophthalmologist at Wills Eye Hospital in Philadelphia and a clinical spokesperson for the American Academy of Ophthalmology who wasn’t involved with the Prima study. “What we don’t know yet is how useful it will be in day-to-day functioning for people.”

Garg says there’s a huge need for this kind of device because AMD is the leading cause of vision impairment in older people. In the US alone, an estimated 20 million Americans have AMD. The number of people worldwide affected by the condition is expected to rise significantly over the next 20 years. “Once that central vision goes bad,” Garg says, “We don’t have any ways to make it better.”