The Prosthetic Eye

Theo – Year 12 Student

Editor’s Note: Year 12 student Theo writes about prosthetic eyes for the GSAL Science Magazine, exploring this developing marvel of modern medicine and how it restores some sight to patients with retinal damage. This is Theo’s second publication in The GSAL Journal; you can read more from Theo here. CPD

[Featured image: A box of glass eyes – predecessors to bionic eyes. (Wellcome Images: Creative Commons)]

Also referred to as a bionic eye, this piece of electrical equipment is implanted into an existing human eye in order to replace the retina and, as such, bionic eyes can only be given to those who have lost their sight as a result of retina damage. This damage may result from retinitis pigmentosa, which is a hereditary condition that results in the degradation of cells required for sight in the retina (the rod and cones cells to be precise). The retina is the tissue at the back of the eye that turns the light entering the eye into a signal that the brain can interpret and results in the ability to see; this is why the prosthetic eye can only give sight to those who have lost their sight due to a problem with the retina as the prosthetic eye performs this exact function only.

The prosthetic eye is made up of two key components. The first of which is the camera. This is attached to a pair of special glasses that the person wears; these emit radio waves that hit the environment in front of the person and are reflected back to the glasses – this in turn feeds the information it has collected from the radio waves to the stimulator microchip. Although this may sound complicated, it is just like how the flash on a camera works: flashing light rays onto the things in front of it and collecting the data of light that bounces off those objects in order to form an image.

The stimulator microchip is the second component of the prosthetic eye and it is responsible for giving the brain the information collected by the camera. In order to do this, it needs access to the optic nerve (which is the nerve responsible for sending the information our eyes collect to our brain); therefore, this stimulator microchip needs to be implanted into an existing eye where it can touch the optic nerve. The stimulator microchip needs access to the optic nerve as it sends the information collected by the camera through electrodes. Electrodes are used in many modern prosthetics as they can hijack nerves and send their own electrical message along them allowing digital information to be turned into something the body can understand. This means the electrodes on the stimulator microchip can turn the digital information that makes up the image in the microchip into an electrical pulse that moves along the optic nerve to the brain. The brain can then turn these electrical impulses into an image, thus allowing the user of a bionic eye to see.

What it is like to see with a bionic eye?

However, the sight provided by the prosthetic eye is nowhere near the level of sight provided by a human eye so it will be a while before we will even consider replacing human eyes with prosthetic ones. The sight provided suffers from several drawbacks:

  • The field of view is only 30o (which is about the size of an outstretched hand) as opposed to a single human eye which has a field of view of nearly 180o, meaning the bionic eye user has a severely restricted view of what is in front of them;
  • The frame rate of the bionic eye is low so the bionic eye users have described the sight as a series of flashes of the world in front of them as opposed to a stream of images the normal human eye sees;
  • A lack of colour as the segment of the electromagnetic spectrum used to form the image is radio waves not visible light, so the bionic eye user is colour blind;
  • A resolution of 54 pixels which is a result of the technique used to gather the information to produce the image, as opposed to the human eye which has a resolution of 576 megapixels, meaning the bionic eye user sees a really blurred image.

All these drawbacks lead to an image like the one on the left becoming like the image on the right:

[Images courtesy of https://medicalxpress.com/news/2017-08-artificial-vision-people-bionic-eyes.html]

This means a user of the bionic eye sees the world as a series of flashing blurry shapes that allows them to make out the approximate size of things in front of them as well as the rough location of them.

Who benefits?

So, as you can imagine, getting a bionic eye does not provide good vision at all and it requires rehabilitation to use it effectively, but it makes a world of difference to people who see nothing. It can turn their life around, which can be appreciated in the interviews conducted by the BBC following the trial of the Argus II Bionic Eye made by the company Second Sight. One man, Keith Hayman, seemed to be very happy with his bionic eye as he said, “Having spent half my life in darkness, I can now tell when my grandchildren run towards me and make out lights twinkling on Christmas trees.” He went on to suggest that it’s not only the emotional benefits, like he had just described, but also practical benefits when he said, “I would be talking to a friend, who might have walked off and I couldn’t tell and kept talking to myself; this doesn’t happen anymore, because I can tell when they have gone.”

Having spent half my life in darkness, I can now tell when my grandchildren run towards me and make out lights twinkling on Christmas trees.

Keith Hayman

Bionic eyes are not a common thing to see on a blind person at the moment as it can only work under specific conditions, such as needing a working optic nerve and an intact eye, so they can only be given those who have lost the function of their retina only. Clinical trials began in 2017 where they were given to 10 people who were then monitored for a year; further clinical trials are still taking place under the funding of the NHS at Moorfields Eye Hospital.

Theo 949019

Bibliography

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