PRIMA Implant: Vision in Geographic Atrophy
A 2 × 2 mm chip allows people with almost zero vision to read again. Over five million people worldwide live with geographic atrophy, a late form of dry age-related macular degeneration (AMD), which can permanently destroy central visual field areas. An international team led by Stanford Medicine has demonstrated with the PRIMA implant for the blind that this lost central vision can be partially restored.
Source: Original Artwork
Introduction
Geographic atrophy (GA) is a late form of dry AMD in which sharply defined areas of the retina in the macula degenerate. This leads to irreversible loss of central vision. It is estimated that around five million people worldwide are affected. . GA accounts for about 20% of cases of legal blindness due to AMD. It is typical that while patients still have blurry peripheral vision, they see "holes" or gray spots in the center of their field of vision. This makes reading, recognizing faces, and performing precise actions extremely difficult.
Pathophysiologically, in GA, the light-sensitive photoreceptors (rods and cones) in the center of the retina die off first. A large proportion of the downstream nerve cells – especially bipolar and ganglion cells – remain intact for a time. This is precisely where PRIMA comes in: it does not replace the entire visual apparatus, but only the defective photoreceptors, and uses the remaining neural circuitry to continue transmitting signals to the brain via the optic nerve.
How the PRIMA Implant Works
PRIMA is a subretinal, photovoltaic micro-implant that replaces the area of destroyed photoreceptors in the center of the macula. The chip is only 2 × 2 mm in size, , consists of 378 individually controllable pixels, and is thinner than a human hair – other descriptions mention about one-third of the hair's thickness. Each pixel functions like a tiny solar panel: when invisible near-infrared light hits the surface, it generates an electrical current that stimulates a small electrode contact, thereby activating the underlying bipolar cells of the retina.
The system includes special glasses with a front camera and a projection module. This translates the captured images into a pattern of near-infrared light and projects it precisely onto the implant in the eye. A pocket-sized processor allows for adjustment of contrast, brightness, and zoom (up to about 12x), making text or signs larger and easier to recognize.
The light is projected in the near-infrared range at about 880 nm. . This range is invisible to intact photoreceptors. This ensures that the remaining peripheral retina is not disturbed, and patients can simultaneously use their natural peripheral vision and the artificially generated central image.
Source: auge-online.de
A subretinal PRIMA implant, visible in the fundus, after successful implantation for vision restoration.
Clinical Study Results
The currently published study is based on the PRIMAvera program, a multicenter investigation with 38 patients with geographic atrophy. in 17 clinics across Europe. All participants were over 60 years old and had a visual acuity worse than 20/320 in the study eye, well below the threshold for independent reading.
Of the initial cohort, 32 individuals completed the one-year follow-up; 27 of them were able to read again afterwards – corresponding to about 84%. 26 of these 32 showed a clinically significant improvement in visual acuity, defined as at least two additional lines on a standardized vision chart. On average, patients improved by five lines, with one person even gaining twelve lines – figures also confirmed in a summary technical report showing an average of 23 gained ETDRS letters (4.6 lines) and a maximum of 59 letters (11.8 lines).
Crucially, these improvements did not only occur in the testing room: patients used the system in everyday life to read books, food labels, and subway signs, supported by the glasses' zoom function and contrast adjustment. One patient describes that before the implantation, she only saw two "black discs" in the center and only with the chip and intensive training could she perceive individual letters and finally whole pages.
Source: smartup-news.de
Simulation of visual perception: Left shows restricted vision in macular degeneration, right shows improved perception of shapes and letters through the PRIMA implant.
Implantation and Risks
The PRIMA implant is implanted during an approximately two-hour surgery under local or general anesthesia, typically as part of a pars plana vitrectomy, which initially involves removing the vitreous humor. The retina is carefully lifted locally, the chip is inserted under the macula, and the retina is then placed back over it so that the implant is positioned in the area of central atrophy.
As with any retinal surgery, complications are possible: in the PRIMAvera study, a total of 26 serious adverse events were observed in 19 out of 38 patients, , including retinal tears, increased intraocular pressure, and subretinal hemorrhages. Almost all of these complications occurred in the first two months after surgery and reportedly largely resolved, with no life-threatening events described.
After the procedure, a multi-month training process begins: patients must learn to interpret the implant's electrical signals as shapes and letters – comparable to neuroadaptation for cochlear implants in hearing. Visual acuity and reading ability continued to increase over the first 6 to 12 months, depending on how long and consistently the affected individuals worked with the system and rehabilitation.
Future Developments
The current generation of PRIMA implant delivers a black-and-white image without grayscale – sufficient for large letters and clear contours, but far from natural vision. The research team is working on software updates to enable true grayscale, which is particularly important for facial recognition and more complex scenes.
Technically, the biggest limitation currently lies in the pixel count: the current chip offers 378 pixels with a side length of approximately 100 µm, , which limits the achievable visual acuity to coarse structures. In preclinical trials, a chip with around 10,000 pixels and significantly smaller pixel sizes of about 20 µm has already been tested, which could potentially enable visual acuity in the range of about 20/80 – possibly even towards 20/20 for specific tasks in combination with digital zoom.
In the long term, researchers are discussing scenarios where patients with such resolution could not only read but also recognize traffic signs safely or work on computers again; whether this would be sufficient for driving depends on regulatory requirements and the actual visual acuity achieved. The development program is already expanding beyond GA – PRIMA will also be tested in the future for other diseases such as retinitis pigmentosa or Stargardt disease, where photoreceptors fail early but some inner retinal layers remain intact.
Source: user-added
A promotional image for Keystone Prima showing two dental implants and German text.
Conclusion
For people with geographic atrophy, there were long only therapies that minimally slowed the progression but could not restore lost vision. With the PRIMA implant for the blind, there is now a system that can restore functional vision such as reading and shape recognition to patients who are practically blind in the center – in a larger patient group and with clearly measurable gains on the eye chart.
The technology is far from delivering "perfect" vision: the images are low-resolution, black-and-white, the system requires surgery with significant risks and months of training, and not all patients benefit equally. However, compared to earlier retinal prostheses, which usually only enabled simple light perception, PRIMA marks a leap towards true form perception – and thus towards abilities that concretely improve daily life and independence.
If the next chip generations with more pixels, grayscale, and better integrated goggle technology actually deliver what initial animal and human studies promise, "I can read the large letters again" could become "I see everything clearly enough for my daily life again."