Hariharan Sivadasan.

Asan Memorial College of Engineering and Technology. Chengalpet.

BIONIC EYE VISUAL PROSTHESIS

BIONIC EYE ?

Bio-electronic eye Electronic device which replaces functionality of

a part or whole of the eye Used for replacing functionality (or) Adding functionality to the eye

The Eye

Human Eye is similar to a camera Macula provides the highest resolution of the image which we see. Macula is comprised of multiple layers of cells which process the initial “analog”light energy entering the eye into “digital” electrochemical impulses. Human eye has nearly 100 million photoreceptors.

Structure of the Eye

The Retina

The Eye with Retina

How does healthy vision work

The human eye captures information that is only perceived once processed by the brain.

The eye receives information via reflected light – it can only make sense of what is in a room if there is some light to illuminate its contents. If it is pitch black, there is nothing for the eye to work with.

Reflected light enters the eye and is focussed on its rear internal surface, known as the retina. Light receptors located on this surface process the light into electrical signals and transmit these signals to the brain along the optic nerve.

When the brain receives this electrical information from the optic nerve, it interprets it as an image.

How the eye does it?

Light enters the eye through the cornea, the clear bulge at the front of the eyeball. The cornea gathers the light into the pupil, a hole in the centre of the iris, which is the structure that gives the eye its colour. 

Depending on the amount of light available to the eye, the iris will contract or expand to accommodate the amount of light required, making the pupil smaller or larger. The more light that is available, the smaller the pupil becomes; restricting the amount of light entering the eye. The less light available, the larger the pupil becomes; allowing more light to enter the eye. 

Once the light passes through the pupil it goes through the crystalline lens, which sits behind the iris. Light then passes through the vitreous humour, the clear gel that fills the inside of the eye. Finally, light comes to focus on the retina.

The retina is a filmy tissue made up of a number of layers of different types of cells. One layer of the retina contains light receptors known as rods and cones. These light receptors allow the retina to convert light into electrical impulses, which are then transmitted along the optic nerve to the brain and decoded into vision.

The macula sits at the centre of the retina and processes fine detail into accurate vision. The fovea, inside the macula, processes even finer detail.

Measuring vision

Visual acuity is the measure of how well someone sees. This can be determined by testing how clearly they can see text at a standard distance. This is done with a Snellen chart, named after its inventor, Herman Snellen, a Dutch ophthalmologist who worked at the turn of the 19th century.

The Snellen Chart

The Snellan chart typically features eleven rows of letters, which are largest on the top row (which usually has one letter only) and smallest on the final row (which usually has nine letters). Each row indicates a specific level of acuity; one row represents what is accepted to be normal vision, a visual acuity of 20/20. 

Many people have visual acuity higher than 20/20 (such as 20/15) and many have a lower visual acuity (such as 20/40). The larger the second number, the lower the visual acuity.

Bionic Eye

Who will it help?

Technology is aimed at helping people with severe vision loss due to:

Retinitis pigmentosa, and Age-related macular degeneration. To benefit from this technology people will need: 

Some remaining retinal ganglion cells A healthy optic nerve and visual cortex Very low or no vision To have been able to see in the past, so that the

vision processing part of the brain has developed fully.

What Might I see?

A person using a retinal implant to see will not experience vision in the same way a person with healthy vision does. Vision will be quite basic to start with and people will need training to adapt to the implant. With time, training and patience, people will be able to use this visual information to be more independent and mobile. 

Phosphene vision and The Bionic Eye apps

The retinal implant bionic eye works by stimulating the perception of light in a patient. A phosphene is a perceived spot of light in the visual field. What our technology aims to do is stimulate many of these phosphenes across the visual field in a way that enables the patient to put together a picture of what they are looking at. The more electrodes an implant contains, the more phosphenes are capable of being generated and the more detail a patient may be able to see. 

An app to simulate the sort of vision a person with a bionic eye might experience. Although it is difficult to predict exactly what people with retinal implants will experience, the app will help you imagine what vision with phosphenes might be like. You can vary phosphene number and size to experience different effects, and also record images of what you are 'seeing' with your bionic vision.

  The bionic eye app is now available for Android and iOS.

How does it work?

The bionic vision system consists of a camera, attached to a pair of glasses, which transmits high-frequency radio signals to a microchip implanted in the eye. Electrodes on the implanted chip convert these signals into electrical impulses to stimulate cells in the retina that connect to the optic nerve. These impulses are then passed down along the optic nerve to the vision processing centres of the brain, where they are interpreted as an image.

To benefit from this technology, patients need to have a functional visual pathway from the retina to the brain along the optic nerve, as well as some intact retinal cells. As such, the two medical conditions that this technology aims to address are retinitis pigmentosa and age-related macular degeneration.

Why these Conditions?

Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are two major causes of blindness and low vision in Australia and worldwide. Both these conditions lead to damage of the photoreceptor cells in the retina that are crucial to vision, but leave the optic nerve and visual cortex healthy and intact.

Approach takes advantage of the healthy parts of the visual system to maximise the benefits for people with RP and AMD.

The BVA devices

Scientists are simultaneously developing different bionic eye devices. From 2012 until 2014 research was conducted with a 24-electrode early prototype that was implanted in three people.

• 44-electrode prototype• Wide-View device• High-Acuity device

44-electrode prototype

The 44-electrode prototype is designed to help researchers learn more about how the bionic eye can be optimised. The device will be fully implantable and include a patient-worn vision processor. Participants will be able to take the device out of the lab and into the real world. Feedback from patients will allow researchers to develop more sophisticated vision processing and stimulation techniques.

High-Acuity device

With the High-Acuity device, Scientists hope patients will be able to recognise faces and read large print. The first patients for the High-Acuity device will be people with retinitis pigmentosa, but scientists are developing the technology so it will be suitable for people with age-related macular degeneration.

Wide-View device The Wide-View device may be most suitable

for patients with retinitis pigmentosa. Researchers continue work on the device development and preclinical studies in preparation for patient tests with this device in due course.

The implanted chip has 98 electrodes to stimulate the retina and enable patients to perceive vision.

To provide patients the ability to move around large objects such as buildings, cars and park benches and to lead more independent lives.

Advantages

Very Early in the visual pathway No Batteries implanted within body No complicated surgical procedure Power Requirement – ¼ of milliwatt

Disadvantages

Axons b/w electrodes and ganglionic cells

Other axons get excited – unwanted perception of large blur

Extra circuitry required for downstream electrical input

Conclusion

Its been 40 years since Arne Larsson received the first fully implanted cardiac pacemaker at the Karolinska Institute in Stockholm.

Researchers throughout the world have looked for ways to improve people's lives with artificial, bionic devices.

Bionic devices are being developed to do more than replace defective parts.

Researchers are also using them to fight illnesses.

Providing power to run bionic implants and making connections to the brain's control system pose the two great challenges for biomedical engineering.

We are now looking at devices like bionic arms, tongues, noses etc.