The Bionic Eye

A bionic eye, also called a visual prosthesis, is an electrical implant that is surgically inserted into the eye. It improves light sensitivity and creates a sense of vision for people who have advanced vision loss. Most of the devices being developed are for individuals who have retinal degeneration caused by diseases like retinitis pigmentosa (RP) and age-related macular degeneration (AMD). There are other devices being studied that bypass the optic nerve and may be useful for people who have other types of vision loss.

What is a retinal prosthesis?

The retina is the part of the eye that senses and sends light signals. It is made of many different cell types which all play a unique role in vision. Photoreceptor cells sense light and start an electrical signal. The signal is passed through a middle layer of retinal cells, the optic nerve and finally to the brain, where an image is formed. Damage or loss of photoreceptor cells causes vision loss in many types of retinal degeneration including inherited retinal diseases like RP, choroideremia and Leber congenital amaurosis and AMD.

A retinal prosthesis acts as artificial retina. It works to replace the function of photoreceptors that have been lost during retinal degeneration. Using components like cameras, computers and electrodes, the prothesis captures light and converts it into an electric signal. This signal goes to the brain and creates a new simulation of vision. This is different than an implanted lens or a low-vision device, which tries to maximize a person’s existing vision.

Who could use it

Retinal prostheses are for people who are blind or have only minimal light perception but who once had sight. All of the prostheses currently being studied require a developed visual cortex, the part of the brain that processes light signals to form images. This means that users need to have been able to see previously for these devices to work.

Retinal prostheses also require a healthy optic nerve to work. These devices have been tested on individuals with advanced stage inherited retinal disease (IRD), mainly RP. If successful, the devices may be a treatment option for many types of IRD or other types of retinal degeneration like AMD.

Will a prosthesis restore my vision?

The prostheses that have been tested so far do not fully restore sight but can produce some visual sensation. Users may be able to distinguish between light and dark and recognize shapes. For example, people have been able to recognize a doorway or the shape of a person, or in some cases can tell the difference between a fork and a spoon. Retinal prostheses provide a “simulation of sight.” This means users have to re-learn how to see and train their brains to interpret this new kind of information. The results can vary widely from person to person.

How do retinal prostheses work?

Just as there are different kinds of smartphones, there are different types of retinal prostheses.

Retinal protheses include both internal and external components. External components may include glasses, tiny computers and power supplies. Internal components can include electrodes or microchips. The internal part of the retinal prosthesis can be placed in different parts of the retina. Most are surgically placed on the retina surface (epiretinal) or just outside the retina (subretinal).

An epiretinal prosthesis simulates the retina’s remaining cells, allowing for signals to be sent to the brain to create the sensation of vision. This type of prosthesis is easier to implant than a subretinal prosthesis. Epiretinal prostheses require an external camera to capture visual information, requiring users to scan an area or item with their head rather than as we normally would with our eyes.

The Argus II is an example of an epiretinal prosthesis. It is composed of a tiny microchip implanted on the front of the retina, and a mini camera embedded in glasses. The camera captures images and converts them to electrical impulses sent wirelessly to the electrodes. The impulses stimulate the retina’s remaining cells which send messages to the brain. The brain then interprets these messages as an image. Over time, patients can regain some functional vision.

A subretinal prosthesis stimulates the middle layer of retinal cells, which then pass the signal to the optic nerve. Researchers believe that using existing cell layers to help process the light signal should result in more accurate vision. However, these devices will only work if this middle layer of cells has not been damaged.

The Alpha IMS and Alpha AMS are examples of subretinal prostheses. They are currently approved in Europe but not in Canada or the United States. In these devices, a silicon chip is implanted behind the retina. It is connected to a tiny computer located behind the ear and to an external battery pack which amplifies the light signal. This power supply can be worn around the neck. These devices do not use external glasses making them less bulky, but they also have less processing power.

A third type of retinal prosthesis is a suprachoroidal implant placed between the choroid and the sclera in the eye. No suprachoroidal prostheses have been approved as a treatment yet.

What is a cortical prosthesis?

Some visual prostheses are not placed near the retina at all. These include devices that are implanted on the optic nerve or parts of the brain such as the thalamus or the visual cortex. For example, devices like the Gennaris by Monash Vision Group or the Orion by Second Sight are implanted on the surface of the brain’s visual cortex. They are paired with a mini camera in glasses that wirelessly sends visual information to the brain. The potential benefits of implanting a device on the brain is that it bypasses the diseased eye and can treat several causes of blindness. These devices might be treatment options for individuals with different types of eye disease such as glaucoma, optic nerve damage, IRDs and AMD.

retinal prostheses that are approved in Canada

The Argus II was the only retinal prosthesis approved for use in Canada. Fighting Blindness Canada played a key role in bringing the Argus II (sometimes called the Bionic Eye) to Canada by helping to fund an observational clinical trial of the device at the Toronto Western Hospital led by Dr. Robert Devenyi. However, in the last few years Second Sight has stopped supporting this device, meaning that it is no longer being sold and individuals who have the device may not receive support or repairs in the future.

The Argus II was also the only retinal prosthesis approved in the United States. Currently, there are four approved prostheses in Europe, the Argus II, Alpha IMS, Alpha AMS, and IRIS II bionic vision system. Other types of retinal prostheses are being studied in clinical trials around the world.

New and ongoing research

Many types of prostheses are being developed or studied, including the IRIS II, EPI-RET3, Boston Retinal Implant Project (BRIP), Photovoltaic Retinal Implant (PRIMA) bionic vision system, Bionic Eye System by Bionic Vision Technologies, Phoenix 99, and the suprachoroidal–transretinal stimulation (STS) system. Research is being done to create new devices as well as improving outcomes with existing devices. Prostheses are being refined to make the lifespan of devices longer, improve quality of life with more powerful and smaller devices, expand the field of vision, increase the number of electrodes, and improve clarity and sharpness of vision.

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