Prima retinal prosthesis tackles advanced macular degeneration

27 Oct 2025

Stanford Medicine implant restores enough vision to allow reading of books and subway signs.

A clinical trial led by Stanford University School of Medicine has demonstrated that a wireless retinal prosthesis can help restore vision lost to advanced macular degeneration.

The results, published in the New England Journal of Medicine, showed that 27 out of 32 participants had regained the ability to read a year after receiving the device.

With digital enhancements enabled by the device, such as zoom and higher contrast, some participants could read with acuity equivalent to 20/42 vision.

The prosthesis used is the Prima device, based on Stanford technology developed at the lab of Daniel Palanker. Early clinical development of Prima was undertaken by Paris-based Pixium Vision, which hailed Prima as a "next-generation miniaturized sub-retinal implant."

In 2024 Pixium's assets, including the Prima technology, were acquired by California's Science Corporation. Prior to the acquisition Science Corporation had been developing a retinal prosthesis named the Science Eye, and working on combining optogenetic gene therapy with an implanted microLED display.

Prima exploits the way that macular degeneration features the loss of functioning photoreceptors but leaves the intermediate nerve cells, to which the receptors would have relayed signals, intact. Each pixel on a chip implanted in the retina produces an electrical current corresponding in intensity to the amount of light it receives, stimulating those nearby functioning retinal nerve cells.

A small clinical trail of five patients in 2020 confirmed that a chip inserted in the retina and activated by augmented reality glasses worn by the patient could deliver a partial but substantial return of central vision. The new trial expanded the cohort, enrolling its AMD participants across 17 clinical sites in five countries.

Using vision to the fullest

The Prima chip is sensitive to infrared light projected from the glasses, unlike natural photoreceptors that respond only to visible light. This design allows patients to continue to use their natural peripheral vision through visible light acting on the working peripheral photoreceptors, while Prima handles central vision.

"The projection is done by infrared because we want to make sure it's invisible to the remaining photoreceptors outside the implant," said Prima developer Daniel Palanker said. "The fact that they see simultaneously prosthetic and peripheral vision is important because they can merge and use vision to its fullest."

Of the 32 patients who completed the one-year trial, 27 could read and 26 demonstrated clinically meaningful improvement in visual acuity, which was defined as the ability to read at least two additional lines on a standard eye chart, said Stanford. On average, participants' visual acuity improved by 5 lines; one improved by 12 lines.

The participants used the prosthesis in their daily lives to read books, food labels and subway signs. The glasses allowed them to adjust contrast and brightness and magnify up to 12 times, and two-thirds reported medium to high user satisfaction with the device.

For now the Prima device provides only black-and-white vision, with no shades in between, but Palanker is developing software that will soon enable the full range of grayscale. A next-generation version already tested in rats may feature 10,000 pixels per chip, compared to the 378 in the current device.

"This is the first version of the chip, and resolution is relatively low,” commented Palanker. "The next generation of the chip, with smaller pixels, will have better resolution and be paired with sleeker-looking glasses."