The future of vision: Bionic eyes and eye implants

What is a visual prosthesis?

A visual prosthesis is also called a "bionic eye.” It’s a surgically implanted electronic device. It can help people with vision loss caused by photoreceptor cell degeneration. These are individuals who have lost partial or full function of the eye’s light-sensing cells. 

This includes people with retinitis pigmentosa (RP) or macular degeneration. Bionic eye technology can mimic some of the eye’s natural processes, such as:

1. Capturing light.
2. Converting the light into electrical signals.
3. Sending the signals to the retina (the light-sensitive tissue at the back of the eye).

A bionic eye does not provide full vision restoration. However, it can create some functional sight.

How bionic eyes work

A bionic eye works with the healthy parts of the eye to help create functional vision. When light enters a healthy eye, it lands on the retina at the back of the eye. A cascade follows:

1. Specialized cells in the retina (called photoreceptors) capture this light.
2. The light is converted into electrical signals.
3. These signals travel through several layers of processing cells within the retina.
4. These processing cells refine and interpret the information.
5. Specialized cells called ganglion cells receive these refined signals.
6. They send the signals along the optic nerve (a bundle of connecting fibers) to the brain.
7. The image is understood and perceived.

Retinitis pigmentosa and macular degeneration are progressive eye diseases. They cause photoreceptors and processing cells to gradually die. Fortunately, the ganglion cells often remain healthy and functional for much longer. A visual prosthesis can bypass damaged retinal cells. It can communicate directly with surviving ganglion cells.

Components of a bionic eye

As technology advances, the components of bionic eyes will continue to evolve. The components of a bionic eye can include:

• A camera – Mounted on glasses and captures the user’s field of view.
• A processing unit – This component extracts important features from the visual scene. It then converts this information into specific electrical stimulation patterns.
• A wireless link – The processing unit wirelessly transmits power and data to the internal implanted system.
• An implanted system – This system includes a receiver/decoder and a multi-electrode array.
• A multi-electrode array – This array is implanted along the visual pathway. This includes the retina, optic nerve and visual cortex. It generates electrical stimulation waveforms that activate neurons. This allows the brain to interpret the resulting light patterns.

The science behind eye implants

Researchers have developed two main methods for restoring vision:

Camera-assisted systems (external processing)

In this system, a microelectrode array is placed inside the eye. It contains specialized electrodes and relies on external components. The individual then wears a pair of specialized glasses with a built-in camera: 

1. The camera captures images of its surroundings.
2. A wearable processor converts these images into electrical signals. 
3. It then sends them to the implant near the eye. 
4. This implant transmits signals to the microelectrode array, which stimulates retinal ganglion cells.
5. The ganglion cells send signals to the brain via the optic nerve.
6. The result is a black and white visual image. This can help restore some functional vision.

The ARGUS II bionic eye (no longer in production) was a well-known example of this system. It was designed to bypass the damaged parts of the retina. It communicated directly with surviving ganglion cells.

Light-sensitive systems (internal processing)

This newer system uses a special electrode array made of photodiodes. These tiny components capture light. They convert it into electrical signals without the need for an external camera. They can respond directly to light, eliminating the need for complex wiring inside the eye.

The photodiode method has several advantages:

• It uses a light-conversion process, often eliminating the need for implanted cables.
• The surgery is simpler and less invasive.
• It doesn’t require an external camera.
• Eye movements can align naturally with what is seen.
• The connection between eye movement and visual perception is better maintained.

Bionic eye technology

A bionic eye implant requires precise communication with the retinal nerve cells. This requires careful attention to the system's design and biological compatibility.

Microelectrodes and neural interfacing

The microelectrodes are the tiny components that deliver electrical signals. They must be highly localized. They must also be comparable in size to the target nerve cells. This precision ensures that the eye implant stimulates individual cells. When a broad area is activated, it could result in blur or distortion.

Bioelectronics and biocompatibility 

Carefully engineered implants can coexist safely within the eye. When an implant is placed inside the eye, the body's natural response is to view it as foreign. To minimize this reaction, eye implant materials must be selected for their biocompatibility. Biocompatibility means the materials integrate well with eye tissue. It must be unlikely to trigger rejection or inflammation. 

Long-term stability

The materials used for a bionic implant must be proven safe in clinical practice. The materials must also resist degradation over time. They need to maintain their structural integrity. This ensures the device functions reliably throughout the patient's life.

Types of bionic eye implants

Retinal prostheses are the most common type of bionic eye. They are designed to directly stimulate remaining retinal neurons. This can help users perceive light, detect motion and recognize large objects.

The PRIMA system

The photovoltaic retinal implant (PRIMA) system was developed by Stanford Medicine researchers. PRIMA is a completely wireless device. It uses photovoltaic pixels implanted under the retina. These convert pulsed near-infrared light from special glasses into electrical stimulation.

The system includes a camera in eyeglasses. It also has a projector to beam images using near-infrared light to the PRIMA microchip in the eye. The device is the first eye prosthesis to restore functional sight. It has allowed patients with incurable vision loss to recognize shapes, patterns and letters.

The Argus II system

The Argus II Retinal Prosthesis System was a landmark bionic eye device. Its manufacturer discontinued production in 2019 to focus on a next-generation cortical implant. This left more than 350 existing users without long-term support.

Benefits and challenges of bionic eyes

For eligible patients, bionic eyes offer several benefits:

• Functional vision capabilities – Devices like PRIMA have demonstrated the potential to restore functional vision. This includes the ability to read and recognize letters.
• Enhanced independence and mobility – Bionic eyes can improve spatial awareness. They can help users detect motion and locate high-contrast objects. This allows for increased independence.
• Improved quality of life – Regaining even partial vision can enhance a patient's quality of life. It can also help psychological well-being. It can allow them to perform basic tasks, such as walking through a door without assistance.

Despite its successes, bionic eye technology faces challenges:

• High cost and limited access – Developing visual prostheses is expensive. It requires extensive research and trials. This high cost restricts affordability and access.
• Long-term support and obsolescence risk – Manufacturers have faced financial difficulties, and some have discontinued previously approved devices. This raises concerns about long-term support and the risk of device failure in the future.
• Technical limitations – Current technology provides low-resolution, pixelized vision with a limited field of view. 
• High complexity – The procedures are complex. They require extensive rehabilitation and patient effort. The user must learn how to interpret the artificial electrical signals. 
• Surgical specialization – The complexity entailed confines procedures to relatively few specialized surgical centers.
• Variable outcomes and strict requirements – Outcomes vary between patients and candidacy requirements are rigorous.

Future prospects in bionic eye technology

Bionic eye technology is no longer just an idea. The PRIMA system has shown that patients with dry AMD can regain meaningful vision.

Advanced retinal implants

Next-generation retinal prostheses — such as the PRIMA subretinal system — are rapidly improving. Ongoing work on smaller pixels is expected to improve visual acuity. This will be paired with digital zoom and contrast enhancement in smart glasses. Some patients may one day achieve functional acuity approaching normal vision.​ 

Brain-based visual implants (cortical prostheses)

Cortical visual prostheses directly stimulate the visual cortex. They bypass the eyes and optic nerves entirely. This makes them promising for people who cannot benefit from retinal implants. This includes those with severe optic nerve damage and people with certain forms of congenital blindness. 

Early systems have explored patterned cortical stimulation. This can allow users to perceive simple shapes and high-contrast targets on a screen. 

Newer devices include Neuralink’s Blindsight system. These devices are designed to restore vision by directly activating the visual cortex. The Blindsight system has received FDA approval for clinical trials.

The path forward for bionic vision

Brain-based implants are giving hope to those with severe damage to the optic nerve. Currently, the artificial vision created by current implants differs from natural sight. Most patients describe seeing grainy, low-resolution images. Others report seeing flickering white lights, which researchers call phosphenes. 

This artificial vision is limited, but it still provides valuable information. It can help patients navigate their surroundings and understand their environment.

Researchers are working to combine implants with advanced artificial intelligence (AI) algorithms. The AI is trained to extract the most important visual features from the camera's images. It could then translate these key features into signals delivered to the brain. 

The field is advancing toward improvements in:

• Improved technology – Images will be clearer and the field of view will be wider. The devices will last longer without causing eye problems.
• Increased affordability and availability – Insurance companies may begin to cover a greater share of the cost. More hospitals worldwide will be trained to perform the surgery. Resources to help patients learn to use the devices will become more widely available.
• Long-term patient support – Companies will commit to long-term support of patients who use their devices.

If you’re interested in bionic eye technology, speak with your eye doctor. They can determine if you are a candidate. Your ophthalmology or optometry office can assist you with any questions.