Retinal Prostheses: How Bionic Eye Technology Works
Understanding Retinal Prostheses
A retinal prosthesis is a small electronic device implanted inside or near the retina, the light-sensitive tissue at the back of the eye. In conditions like retinitis pigmentosa (RP), the photoreceptors (the cells that detect light) gradually stop working. A retinal prosthesis does not repair these damaged cells. Instead, it uses tiny electrodes to stimulate the remaining retinal cells that can still send signals through the optic nerve to the brain.
The brain interprets these electrical signals as patterns of light called phosphenes. Phosphenes are not the same as natural vision. They appear as small spots or flashes of light. When enough phosphenes are produced in an organized pattern, a person may detect shapes, movement, and the general layout of a space.
Most retinal prosthesis systems have three main parts. The first is a small camera mounted on glasses worn by the patient. The second is a portable video-processing unit that the patient carries. The third is the implant itself, which sits on or near the retina inside the eye.
Images captured by the camera are sent to the processing unit. This unit converts them into a pattern of electrical signals. These signals are transmitted wirelessly to the implant. The implant then stimulates surviving retinal cells using its electrode array. The brain receives these signals and learns to interpret them as visual information over time.
Researchers have developed several types of retinal implants, each placed in a different location relative to the retina. The main types include the following:
- Epiretinal implants sit on the inner surface of the retina and stimulate the ganglion cells (the cells that connect to the optic nerve).
- Subretinal implants are placed beneath the retina and stimulate the middle layers of retinal cells.
- Suprachoroidal implants are placed between the choroid (a layer of blood vessels behind the retina) and the sclera (the white outer wall of the eye).
Who May Benefit and Risk Factors
Retinitis pigmentosa (RP) is the main condition for which retinal prostheses have been developed. RP is a group of inherited genetic diseases that cause a slow, progressive loss of photoreceptors. It affects an estimated 1 in 4,000 people in the United States (NIH, 2023). The disease typically begins with difficulty seeing in dim light during childhood or adolescence. Over time, the visual field narrows until many patients reach legal or functional blindness.
RP has been linked to more than 100 different gene mutations (NEI, 2024). These mutations are inherited from one or both parents or arise spontaneously. Because the condition is genetic, there is currently no way to prevent it.
While RP has been the primary focus, researchers are studying whether retinal prostheses could help people with other forms of severe vision loss. Age-related macular degeneration (AMD) and diabetic retinopathy are among the conditions being explored. These conditions damage different parts of the retina. The implant design and placement may need to be adapted for each disease.
Not everyone with vision loss is a candidate. The approved devices were designed for adults with advanced RP who have very little remaining vision. This is generally limited to bare light perception or less. Candidates must have enough healthy retinal cells remaining to respond to electrical stimulation (CMS Technology Assessment, 2014).
A retina specialist evaluates each patient individually. The health of the optic nerve is also an important factor in determining candidacy.
Signs and Symptoms of Conditions Treated
The earliest and most common symptom of RP is poor night vision, also called night blindness. People with RP may notice that it takes much longer than normal for their eyes to adjust in a dark room. They may also have difficulty navigating in low-light environments.
Some patients notice flickering lights or brief flashes in their side vision. These visual disturbances may come and go. They are often among the first signs that something is affecting the retina.
As RP advances, patients experience a slow, steady narrowing of their visual field. This is sometimes described as tunnel vision. The side (peripheral) vision gradually disappears while central vision may be preserved for a longer time. Eventually, central vision is also affected.
The rate of progression varies depending on the specific genetic mutation. Some people retain useful vision into their 50s or 60s. Others reach severe vision loss much earlier. When photoreceptor loss becomes extensive enough that a person can perceive only light or no light, a retinal prosthesis may be considered.
Diagnosis and Testing
A retina specialist diagnoses RP through a comprehensive eye examination. A dilated eye exam allows the specialist to look at the retina directly. The specialist checks for characteristic changes such as dark pigment deposits sometimes called bone spicule pigmentation.
Additional tests typically include the following:
- Electroretinography (ERG), which measures the electrical activity of the retina in response to light.
- Visual field testing, which maps the extent of peripheral vision loss.
- Optical coherence tomography (OCT), which produces cross-sectional images of the retina to assess its structure.
- Genetic testing, which can identify the specific gene mutation responsible.
If a patient has advanced RP with very little remaining vision, a retina specialist may discuss whether a retinal prosthesis could be appropriate. The evaluation assesses residual retinal function and whether the optic nerve can still transmit signals. Imaging tests and electrophysiological studies help determine this.
The patient's overall health, ability to undergo surgery, and willingness to commit to rehabilitation training are also considered.
Treatment Options and Available Devices
The Argus II Retinal Prosthesis System, developed by Second Sight Medical Products, was a landmark device. On February 14, 2013, the FDA approved it as the first implanted device to treat adults with advanced RP. It also received regulatory approval in Europe. More than 350 patients worldwide received an Argus II implant (AAO EyeNet).
The Argus II was an epiretinal device placed on the inner surface of the retina. It used a 60-electrode array to stimulate retinal ganglion cells. Patients reported detecting light, perceiving movement, and in some cases identifying outlines of objects and people. Second Sight Medical Products lost funding and closed during the COVID-19 pandemic. The Argus II is no longer manufactured or supported.
Several other retinal prosthesis systems received regulatory approval, though all have since been discontinued. These include the Alpha IMS and Alpha AMS, developed by Retina Implant AG and approved in Europe. These were subretinal devices using a microchip placed beneath the retina. The IRIS II system also received a CE mark in Europe but was discontinued.
The discontinuation of these devices highlights challenges of bringing this technology to market. The devices are complex and expensive to manufacture. They serve a relatively small patient population. The knowledge gained from these systems continues to inform future devices.
The Photovoltaic Retinal Implant (PRIMA) bionic vision system represents a newer approach. Unlike earlier devices, the PRIMA system is completely wireless. It uses tiny photovoltaic (light-powered) pixels implanted beneath the retina. A small projector built into glasses sends pulses of near-infrared light to these pixels. The pixels convert the light into electrical current to stimulate retinal cells.
In a study involving 38 participants with geographic atrophy (an advanced form of dry AMD), the PRIMA system provided central vision improvement from baseline to 12 months (Pixium Vision clinical data). This is notable because it extends potential use beyond RP to include AMD.
Researchers are exploring new strategies that could complement or eventually replace traditional implanted devices. One promising area involves nanoparticles, tiny particles injected directly into the retina. In animal studies, nanoparticles successfully stimulated the visual system in mice with retinal disorders.
Other experimental approaches include the following:
- Optogenetics, a technique that uses genetic engineering to make surviving retinal cells sensitive to light.
- Cell-based therapies that aim to replace lost photoreceptors with healthy cells grown from stem cells.
- Gene therapies such as Luxturna (voretigene neparvovec), which is FDA-approved for inherited retinal dystrophy caused by RPE65 gene mutations.
What to Expect
Implanting a retinal prosthesis requires surgery performed by a retina specialist (vitreoretinal surgeon). The surgery is done under general anesthesia and typically takes several hours. The surgeon performs a vitrectomy (a surgery to remove the gel inside the eye). The electrode array is then carefully positioned on or near the retina.
As with any eye surgery, there are risks. These may include infection, bleeding, retinal detachment, and inflammation. The retina specialist discusses all potential risks and benefits before surgery.
Receiving a retinal prosthesis is not like flipping a switch. After the implant heals, patients must go through extensive rehabilitation to learn how to interpret phosphene patterns. This training is provided by a specialized team. It may take weeks to months.
Patients learn to associate patterns of light with real-world objects and movements. Head scanning, in which the patient moves their head to direct the camera, is a key skill. Over time, many patients improve their ability to navigate rooms and detect doorways. The visual experience is very different from natural sight. Expectations must be realistic.
Retinal prostheses do not provide natural sight. The resolution of current devices is far lower than what the healthy eye produces. Patients typically gain the ability to perceive light, detect motion, and recognize high-contrast shapes. For someone living in near-total or total darkness, even this limited visual information can be meaningful.
Results vary from patient to patient. Outcomes depend on factors such as remaining retinal cell health, optic nerve strength, and effort invested in rehabilitation training.
Living With a Retinal Prosthesis
Patients who receive a retinal prosthesis continue to rely on other senses and assistive tools. The prosthesis supplements existing orientation and mobility skills. Many users find it most helpful in specific situations, such as detecting whether lights are on, finding doorways, and sensing movement.
The external components, including camera glasses and processing unit, must be worn whenever the patient uses the device. The equipment needs regular charging and maintenance. Follow-up appointments with a retina specialist are needed to monitor the implant.
Receiving a retinal prosthesis can be emotional. For many patients, perceiving light again after years of blindness is profoundly meaningful. At the same time, the gap between expectations and reality can be challenging. The device does not provide detailed, colorful vision. Open conversations with the retina specialist and rehabilitation team before surgery help patients set realistic goals.
Support from family, friends, and vision loss support groups can help patients adjust. Many organizations dedicated to RP and blindness offer resources and peer connections.
One difficult reality is the discontinuation of devices by manufacturers. When Second Sight closed, Argus II patients lost access to technical support, replacement parts, and software updates. This raised important ethical and practical questions about long-term responsibility for implanted medical devices.
Patients considering any implanted technology should discuss the long-term outlook with their retina specialist. This includes what happens if the manufacturer stops supporting the device. Advocacy groups continue to push for better protections.
When to See a Retina Specialist
Anyone who notices difficulty seeing at night, a narrowing field of vision, or unexplained flickering lights should see a retina specialist. These can be early signs of RP or other retinal diseases. Early diagnosis allows for better monitoring and planning.
Family members of people diagnosed with RP should also consider evaluation and genetic testing. The condition is inherited and may be present before symptoms appear.
Patients with advanced RP who have lost most or all functional vision may want to ask about retinal prosthesis options. While current device availability is limited, new systems like PRIMA and experimental technologies are in development. Staying informed and maintaining a relationship with a retina specialist ensures access to new options as they become available.
If a patient experiences any sudden change in vision, such as a sudden increase in floaters, flashes of light, a shadow or curtain over part of the visual field, or sudden vision loss in one eye, they should see a retina specialist or go to the emergency room immediately. These symptoms may indicate a serious condition like retinal detachment.
Questions and Answers
No. Current retinal prostheses provide a basic form of vision consisting of light patterns and shapes. The resolution is much lower than natural sight. Patients can typically detect light, perceive motion, and identify high-contrast outlines. They cannot read standard print, recognize faces in detail, or see in color with current devices. The technology supplements other senses and mobility skills.
Availability is currently limited. The Argus II, the most widely implanted device, is no longer manufactured after the company closed. The PRIMA bionic vision system is in clinical trials and has shown promising results for patients with geographic atrophy due to AMD. Several other devices are in various stages of research. Patients should speak with a retina specialist about what may be available through clinical trials.
Retinal prostheses were originally developed for advanced RP. The FDA approved the Argus II specifically for adults with severe RP. Newer systems like PRIMA are being studied for geographic atrophy, an advanced form of dry AMD. Researchers are also exploring potential applications for other conditions that cause extensive photoreceptor loss, though these are still in early stages.
Rehabilitation generally takes several weeks to several months of regular training sessions. Patients work with a specialized team to learn how to interpret phosphene patterns. Skills like head scanning and pattern recognition improve gradually with practice. Some patients continue to improve over a year or more as they gain experience.
This is a real concern that has affected Argus II patients. When Second Sight closed, patients lost access to technical support, software updates, and replacement parts. The implant remains in the eye but may lose functionality over time without support. This issue has prompted discussion about long-term support plans for patients with implanted devices. Patients considering a retinal prosthesis should discuss this with their retina specialist before surgery.