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Bionic Eye: A Look into Current Research and Future Prospects

Dept. of IT, GSSSIETW, Mysore 1

Chapter 1

INTRODUCTION

Technology has done wonders for the mankind. We have seen prosthetics that

helped overcome handicaps. Bio medical engineers play a vital role in shaping the course

of these prosthetics. Now it is the turn of Artificial Vision through Bionic Eyes.

Chips are designed specifically to imitate the characteristics of the damaged

retina, and the cones and rods of the organ of sight are implanted with a microsurgery.

Whether it be Bio medical, Computer, Electrical, or Mechanical Engineers all of them

have a role to play in the personification of Bionic Eyes. There is hope for the blind in the

form of Bionic Eyes. This technology can add life to their vision less eyes!

Sooner or later, this shall create a revolution in the field of medicine. It is

important to know few facts about the organ of sight i.e. the Eye before we proceed

towards the technicalities involved.

1.1 The Eye

Our ability to see is the result of a process similar to that of a camera. This isshown in fig 1.1. In a camera, light passes through a series of lenses that focus images

onto film or an imaging chip. The eye performs a similar function in that light passes

Fig 1.1: Eye-camera similarity.


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through the cornea and crystalline lens, which together focus images onto the retinathe

layer of light sensing cells that lines the back of the eye. The retina represents the film in

our camera. It captures the image and sends it to the brain to be developed.

Once stimulated by light, the cells within the retina process the images by

converting their analog light signals into digital electro-chemical pulses that are sent via

the optic nerve to the brain. A disruption or malfunction of any of these processes can

result in loss of vision.

1.2 How are We Able to See?

For vision to occur, 2 conditions need to be met:

a) An image must be formed on the retina to stimulate its receptors (rods and cones).

b) Resulting nerve impulses must be conducted to the visual areas of the cerebral cortex

for interpretation.

Fig 1.2: The Eye

Four processes focus light rays, so that they form a clear image on the retina:

1. Refraction of light rays

2. Accommodation of the lens

3. Constriction of the pupil

4. Convergence of the eyes


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1.3 Retina

The retina is the innermost layer of the wall of the eyeball. Fig 1.3 shows the

structure of Retina and fig 1.4 shows the Eye with Retina. Millions of light sensitive cells

there absorb light rays and convert them to electrical signals. Light first enters the optic

(or nerve) fiber layer and the ganglion cell layer, under which most of the nourishing

blood vessels of the retina are located. This is where the nerves begin, picking up the

impulses from the retina and transmitting them to the brain.

The light is received by photoreceptor cells called rods (responsible for peripheral

and dim light vision) and cones (providing central, bright light, fine detail, and colour

vision). The photoreceptors convert light into nerve impulses, which are then processed

by the retina and sent through nerve fibers to the brain. The nerve fibers exit the eyeball at

the optic disk and reach the brain through the optic nerve. Directly beneath the

photoreceptor cells is a single layer of retinal pigment epithelium (RPE) cells, which

nourish the photoreceptors. These cells are fed by the blood vessels in the choroids.

LIGHT

Fig 1.3: Retina


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Fig 1.4: The retinal layers

1.4 Retinal Disease

There are two important types of retinal degenerative disease:

a) Retinitis pigmentosa (RP), and

b) Age-related macular degeneration (AMD)

They are detailed below.

Retinitis Pigmentosa (RP) is a general term for a number of diseases that

predominately affect the photoreceptor layer or light sensing cells of the retina. These

diseases are usually hereditary and affect individuals earlier in life. Injury to the

photoreceptor cell layer, in particular, reduces the retinas ability to sense an initial light

signal. Despite this damage, however, the remainder of the retinal processing cells in

other layers usually continues to function. RP affects the mid-peripheral vision first and

sometimes progresses to affect the far-periphery and the central areas of vision. The

narrowing of the field of vision into tunnel vision can sometimes result in complete

blindness.

Age-related Macular Degeneration (AMD) refers to a degenerative condition

that occurs most frequently in the elderly. AMD is a disease that progressively decreases

the function of specific cellular layers of the retinas macula. The affected areas within

the macula are the outer retina and inner retina photoreceptor layer. As for macular

degeneration, it is also genetically related, it degenerates cones in macula region, causing

damage to central vision but spares peripheral retina, which affects their ability to read


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and perform visually demanding tasks. Although macular degeneration is associated with

aging, the exact cause is still unknown.

Together, AMD and RP affect at least 30 million people in the world. They are the

most common causes of untreatable blindness in developed countries and, currently, there

is no effective means of restoring vision.


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the brain, which is able to perceive patterns of light and dark spots corresponding to

which electrodes have been stimulated. The device receives signals from a pair of glasses

worn by the patient, which are fitted with a camera.

The camera feeds the visual information into a separate image-processing unit,

which makes 'sense' of the image by extracting certain features. The unit then breaks

down the image into pixels and sends the information, one pixel at a time, to the silicon

chip, which then reconstructs the image. Data is broadcasted into the body using radio

waves. It's like a radio station that only has a range of 25 millimeters.

Currently the technology is only able to transmit a 10 x 10 pixel. Participants must

be profoundly blind to be eligible those with even partial vision are excluded due to

the potential risk of visual damage.

The most recent version of the implant features an array of 60 pixels, allowing

users to distinguish between light and dark, and see certain distinct objects. The ultimate

goal, according to the research team, is to allow for reading and face recognition by

increasing the number of pixels to 1,000.

2.2 The Bionic Eye System

Visual prosthetics can be broken into three major groups. First, there are the

devices that use either ultrasonic sound or a camera to sample the environment ahead of

an individual and render the results into either a series of sounds or a tactile display. From

this the person is supposed to be able to discern the shape and proximity of objects in

their path.

The second major form is retina enhancers. These machines supplement functions

of the retina by stimulating the retina with electrical signals which in turn causes the

retina to send the results through the optic nerve to the brain.

The third major category of visual prosthetic is a digital camera that samples an

image and stimulates the brain with electrical signals--either by penetrating into or

placing electrodes on the surface of the visual cortex.


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2.3 Retinal Implant Systems

Now, a company called Second Sight has received FDA approval to begin U.S.

trials of a retinal implant system that gives blind people a limited degree of vision.

Second Sights first generation Argus 16 implant consists of a 16 electrode array and a

relatively large implanted receiver implanted behind the ear. The second generation

Argus II is designed with a 60 electrode array and a much smaller receiver that is

implanted around the eye.

It (Argus II) is an array of electrodes that is surgically implanted onto the retina

the layer of specialized cells that normally respond to light found at the back of the eye.

This array of electrodes is able to send signals to the brain that the persons biological

retina is unable to send. Of course, the electrode array is not very useful unless it is

receiving visual data to send to the brain. To solve this problem the patient is fitted with a

pair of glasses that contain a tiny video camera that continuously records footage of what

is in front of the patient. This video signal is sent wirelessly to a wearable computer that

first filters and processes the video signal and then feeds this formatted data to the

electrode array. A picture of the entire setup can be shown in fig 2.1.

Fig 2.1: Argus II


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The Argus II Retinal Prosthesis System can provide sight -- the detection of

light -- to people who have gone blind from degenerative eye diseases like macular

degeneration and retinitis pigmentosa. Both diseases damage the eyes' photoreceptors,

the cells at the back of the retina that perceive light patterns and pass them on to the brain

in the form of nerve impulses, where the impulse patterns are then interpreted as images.

The Argus II system takes the place of these photoreceptors.

The second incarnation of Second Sight's retinal prosthesis consists of five main

parts:

a) A digital camera that's built into a pair of glasses. It captures images in real time and

sends images to a microchip.

b) A video-processing microchip that's built into a handheld unit. It processes images

into electrical pulses representing patterns of light and dark and sends the pulses to a

radio transmitter in the glasses.

c) A radio transmitter that wirelessly transmits pulses to a receiver implanted above the

ear or under the eye.

d) A radio receiver that sends pulses to the retinal implant by a hair-thin implanted wire.

e) A retinal implant with an array of 60 electrodes on a chip measuring 1 mm by 1 mm.

The entire system runs on a battery pack that is housed with the video processing

unit. When the camera captures an image -- of, say, a tree the image is in the form of

light and dark pixels. It sends this image to the video processor, which converts the tree-

shaped pattern of pixels into a series of electrical pulses that represent "light" and "dark".

The processor sends these pulses to a radio transmitter on the glasses, which then

transmits the pulses in radio form to a receiver implanted underneath the subject's skin.

The receiver is directly connected via a wire to the electrode array implanted at the backof the eye, and it sends the pulses down the wire. When the pulses reach the retinal

implant, they excite the electrode array. The array acts as the artificial equivalent of the

retina's photoreceptors. The electrodes are stimulated in accordance with the encoded

pattern of light and dark that represents the tree, as the retina's photoreceptors would be if

they were working (except that the pattern wouldn't be digitally encoded).

The electrical signals generated by the stimulated electrodes then travel as neural

signals to the visual center of the brain by way of the normal pathways used by healthy


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eyes -- the optic nerves. In macular degeneration and retinitis pigmentosa, the optical

neural pathways aren't damaged. The brain, in turn, interprets these signals as a tree and

tells the subject, "You're seeing a tree."

2.4Working

The working of Retinal implant system is shown in fig 2.2. Normal vision begins

when light enters and moves through the eye to strike specialized photoreceptor (light-

receiving) cells in the retina called rods and cones. These cells convert light signals to

electric impulses that are sent to the optic nerve and the brain. Retinal diseases like age-

related macular degeneration and retinitis pigmentosa destroy vision by annihilating these

cells.

With the artificial retina device, a miniature camera mounted in eyeglasses

captures images and wirelessly sends the information to a microprocessor (worn on a

belt) that converts the data to an electronic signal and transmits it to a receiver on the eye.

The receiver sends the signals through a tiny, thin cable to the microelectrode array,

stimulating it to emit pulses. The artificial retina device thus bypasses defunct

photoreceptor cells and transmits electrical signals directly to the retinas remaining

viable cells. The pulses travel to the optic nerve and, ultimately, to the brain, which

perceives patterns of light and dark spots corresponding to the electrodes stimulated.

Patients learn to interpret these visual patterns. It takes some training for subjects

to actually see a tree. At first, they see mostly light and dark spots. But after a while, they

learn to interpret what the brain is showing them, and they eventually perceive that

pattern of light and dark as a tree.

Researchers are already planning a third version that has a1000 electrodes on the

retinal implant, which they believe could allow for reading, facial recognition capabilities

etc.

1: Camera on glasses views image

2: Signals are sent to hand-held device

3: Processed information is sent back to glasses and wirelessly transmitted to receiver

under surface of eye

4: Receiver sends information to electrodes in retinal implant


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5: Electrodes stimulate retina to send information to brain.

Fig 2.2: Working of Retinal Implant System


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Chapter 3

OCULAR IMPLANT

Ocular implants are those which are placed inside the retina. It aims at the

electrical excitation of two dimensional layers of neurons within partly degenerated

retinas for restoring vision in blind people. The implantation can be done using standard

techniques from ophthalmic surgery. Neural signals farther down the pathway are

processed and modified in ways not really understood therefore, the earlier the electronic

input is fed into the nerves the better. There are two types of ocular implants: Epi-retinal

implants and Subretinal implants. The ocular implantation is shown in Fig 2.3.

Fig 3.1: Section of the eye showing the retina and its layers. In conditions such as retinitis

pigmentosa and macular degeneration, the light sensing rod and cone cells

("photoreceptors") no longer function. A retinal prosthesis can be placed either on

the retinal surface ("epi-retinal") or below the retina in the area of damaged

photoreceptors ("sub-retinal") to try to stimulate the remaining cells

.


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3.1 Epi-Retinal Implants

The Epiretinal approach involves a semiconductor-based device placed above

the retina, close to or in contact with the nerve fiber layer retinal ganglion cells. The

information in this approach must be captured by a camera system before transmitting

data and energy to the implant.

In the EPI-RET approach scientists had developed a micro contact array which is

mounted onto the retinal surface to stimulate retinal ganglion cells. A tiny video camera is

mounted on eyeglasses and it sends images via radio waves to the chip. The actual visual

world is captured by a highly miniaturized CMOS camera embedded into regular

spectacles. The camera signal is analyzed and processed using receptive field algorithms

to calculate electric pulse trains which are necessary to adequately stimulate ganglion

cells in the retina.

This signal together with the energy supply is transmitted wireless into a device

which is implanted into the eye of the blind subject. The implant consists of a receiver for

data and energy, a decoder and array microelectrodes placed on the inner surface of the

retina. This micro chip will stimulate viable retinal cells. Electrodes on microchip will

then create a pixel of light on the retina, which can be sent to the brain for processing.

The main advantage of this is that it consists of only a simple spectacle frame with

camera and external electronics which communicates wirelessly with microchip

implanted on retina programmed with stimulation pattern.

Fig 3.2: Block diagram of the EPI-RET System


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The issues involved in the design of the retinal encoder are:

a) Chip Development

b) Biocompatibility

c) RF Telemetry and Power Systems

a) Chip Development:

Encoder Epi Retinal

The design of an epiretinal encoder is more complicated than the sub retinal

encoder, because it has to feed the ganglion cells. Here, a retina encoder (RE) outside the

eye replaces the information processing of the retina. A retina stimulator (RS), implanted

adjacent to the retinal ganglion cell layer at the retinal 'output', contacts a sufficient

number of retinal ganglion cells/fibers for electrical stimulation. A wireless (Radio

Frequency) signal and energy transmission system provides the communication between

RE and RS. The RE, then, maps visual patterns onto impulse sequences for a number of

contacted ganglion cells by means of adaptive dynamic spatial filters. This is done by a

digital signal processor, which, handles the incoming light stimuli with the master

processor, implements various adaptive, antagonistic, receptive field filters with the other

four parallel processors, and generates asynchronous pulse trains for each simulated

ganglion cell output individually. These spatial filters as biology-inspired neural networks

can be 'tuned' to various spatial and temporal receptive field properties of ganglion cells

in the primate retina.

b) Biocompatibility:

The material used for the chips and stimulating electrodes should satisfy a variety

of criterias. They must be corrosion-proof, i.e. bio stable.

The electrodes must establish a good contact to the nerve cells within fluids, sothat the stimulating electric current can pass from the photo elements into the

tissue.

It must be possible to manufacture these materials with micro technical methods. They must be biologically compatible with the nervous system.


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c) RF Telemetry:

In case of the epiretinal encoder, a wireless RF telemetry system acts as a channel

between the Retinal Encoder and the retinal stimulator. Standard semiconductor

technology is used to fabricate a power and signum receiving chip, which drives current

through an electrode array and stimulate the retinal neurons. The intraocular transceiver

processing unit is separated from the stimulator in order to take into account the heat

dissipation of the rectification and power transfer processes. Care is taken to avoid direct

contact of heat dissipating devices with the retina.

3.2 Sub Retinal Implants

Fig 3.3: Sub retinal Implant

The Sub retinal approach involves the electrical stimulation of the inner retina

from the sub retinal space by implantation of a semiconductor-based micro photodiode

array (MPA) into this location. The concept of the sub retinal approach is that electrical

charge generated by the MPA in response to a light stimulus may be used to artificially

alter the membrane potential of neurons in the outer retina or remnants of this structure

and thereby activate the visual system. Because the implant is designed to stimulate the

retina at an early stage of the visual system, this approach would theoretically allow the

normal processing networks of the retina to transmit this signal centrally.

In Retinitis pigmentosa disease, the retinal pigment epithelial cells (RPE) begin to

die out and the person starts loosing the vision gradually. Since the function of the retinato transduce light into biological signal is weakened, it causes blindness. Subretinal


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implant is used to substitute the lost RPE cells with the ones of artificial basis to restore

the vision. In this implant, a microphotodiode array (MPD), a silicon micromanufactured

device, or semiconductor microphotodiode array (SMA) is used. This piece of equipment

is placed behind the retina between the sclera and the bipolar cells. The incident light is

transformed into electrical potentials that excite the bipolar cells to form an image

sensation.

The arrays can be manufactured by various silicon manufacturing procedures.

MPD arrays are manufactured consistently with measurements of each stimulating unit as

20 m X 20 m, and adjacent units separated as 10 m. The elements are produced to be

responsive to light corresponding to the visible spectrum (400-700 nm). Several

thousands of the devices can be placed on a single structure of diameter of 3 mm,

thickness of 100 m and with a density same as the replacing RPE cells. These devices

have demonstrated the same electrophysiological behaviours as the healthy RPE cells.

The MPDA has to be very thin and flexible enough in order to be able to fit to the

curvature of the eye ball. Figure below shows an example of such an ultra thin MPDA

having a thickness of 1.5 micron, together with titanium substrate and silicon nitride

passivation.

Fig 3.4: Ultra thin microphotodiode array


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In Subretinal implant, the light-sensitive microphotodiodes with microelectrodes

of gold and titanium nitride set in arrays is implanted in the subretinal space. The visible

light coming from different directions is transformed into small currents by the

microphotodiodes at each of hundreds of microelectrodes. These currents are then passed

to the retinal network by neurons. The middle and inner retina captures current and then

processes the part of vision. There are many benefits of using the subretinal prostheses.

Such as, the MPD directly replaces the lost or degenerated RPE cells; the re tinas

remaining network is still capable of processing electrical signals; ease of fixing the high

density MPDA in the subretinal position; no need of any external camera or external

image processing equipment; and eye movement to locate the objects is not restricted.

There are some of the limitations to the subretinal implants as well. The single

MPD is not enough to stimulate enough current. So a subretinal implant is supported by

an external energy source, such as transpupillary infrared illumination of receivers close

to the chip or electromagnetic transfer, is currently under progress. Some of the additional

developments in this process are movement to flexible substrates to hold the subtle nature

of the retina and to decrease the light intensity.

Fig 3.5: Shows the major difference between epi-retinal &sub retinal approach


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Now, a German firm dubbed Retina Implant has scored a big win for the sub

retinal solution with a three-millimeter, 1,500 pixel microchip that gives patients a 12

degree field of view.

In general,

Epiretinal Approach involves a semiconductor based device positioned on thesurface of the retina to try to simulate the remaining overlying cells.

Subretinal Approach involves implanting the ASR chip behind the retina tosimulate the remaining viable cells.


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Chapter 4

MULTIPLE UNIT ARTIFICIAL RETINA CHIPSET

(MARC)

The other revolutionary bio electronic eye is the MARC; this uses a CCD camera

input and a laser beam or RF to transmit the image into the chip present in the retina.

Using this, a resolution of 100 pixels is achieved by using a 10x10 array. It consists of a

platinum or rubber silicon electrode array placed inside the eye to stimulate the cells.

Fig 4.1: The MARC System

The schematic of the components of the MARC shown in fig 4.1, consists of a

secondary receiving coil mounted in close proximity to the cornea, a power and signal

transceiver and processing chip, a stimulation-current driver, and a proposed electrode

array fabricated on a material such as silicone rubber thin silicon or polyimide with

ribbon cables connecting the devices.

The stimulating electrode array is mounted on the retina while the power and

signal transceiver is mounted in close proximity to the cornea. An external miniature low-

power CMOS camera worn in an eyeglass frame will capture an image and transfer the

visual information and power to the intraocular components via RF telemetry. The

intraocular prosthesis will decode the signal and electrically stimulate the retinal neurons


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through the electrodes in a manner that corresponds to the image acquired by the CMOS

Camera.

Fig 4.2: A 5x5 platinum electrode array for retinal stimulation fabricated on silicone

rubber and used by doctors at JHU

4.1 Working

The MARC system, pictured in the fig 4.3 will operate in the following manner.

An external camera will acquire an image, whereupon it will be encoded into data stream

which will be transmitted via RF telemetry to an intraocular transceiver. A data signal

will be transmitted by modulating the amplitude of a higher frequency carrier signal. The

signal will be rectified and filtered, and the MARC will be capable of extracting power,

data, and a clock signal. The subsequently derived image will then be stimulated upon the

patients retina.

4.1 (a) MARC System Block Diagram

Outside Eye:

The video input to the marc system block is given through a CCD camera. This

image is further processed using a PDA sized image processor & to transmit it, we do

pulse width modulation in first stage and then ASK modulation is done. This signal is

further amplified using a class E power amplifier and transmitted using RF telemetry

coils.

Inside Eye:

The signal received from the RF telemetry coils is power recovered and then these

signal is ASK demodulated and the data and clock is recovered from this signals and


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these signal are sent to the configuration and control block of the chip which from its

input decode what information has to be sent to each of the electrodes and sends them this

data. And the electrodes in turn stimulate the cells in the eye so as to send this stimulation

to the brain through optic nerve and help brain in visualizing the image and while this

process is going on the status of each electrode is sent to the marc diagnostics chip

outside the eye.

Fig 4.3: Block Diagram of MARC System

4.1 (b) Block Diagram of Image Acquisition System

The image acquisition system consists of a CMOS digital camera which acquires

images and sends it to the Analog to Digital Converter. It converts this analog input to

Fig 4.4: Block Diagram of Image Acquisition System


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digital data. This data is first sent into a video buffer where it is processed, the images are

color mapped and these processed images are sent through RS232 interface. This serial

data is then sent to the electrodes or testing monitor through a RF circuit or laser beam.

4.2Advantages of the MARC System Compact Size6x6 mm Diagnostic Capability Reduction of stress upon retina Heat dissipation problems are kept to a minimum


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Chapter 5

APPLICATIONS PROPOSED

Adding displays directly onto the lenses, visible to the wearers but no oneelse, could project critical information like routes, weather, vehicle status onto

windshields for drivers or pilots or superimpose computer images onto real-world

objects for training exercises.

Besides visual enhancement, noninvasive monitoring of the wearers biomarkersand health indicators could be extremely useful. Several simple sensors that can

detect the concentration of a molecule, such as glucose have been built onto

lenses. These would let diabetic wearers keep tabs on blood-sugar levels without

needing to prick a finger.

Lenses remain in contact, through fluids, with the interior of the body and anappropriately configured contact lens could monitor cholesterol, sodium, and

potassium levels, to name a few potential targets. Coupled with a wireless data

transmitter, the lens could relay information to medics or nurses instantly, without

needles or laboratory chemistry.

Bionic lenses could aid people with impaired hearing. Future versions, the scientists believe, they could serve as a flexible plastic

platform for applications such as surfing the Internet on a virtual screen,

immersing gamers in virtual worlds.


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Chapter 7

CONCLUSION

This is a revolutionary piece of technology and really has the potential to change

people's lives. Artificial Eye is such a revolution in medical science field. Its good news

for patients who suffer from retinal diseases. A bionic eye implant that could help restore

the sight of millions of blind people could be available to patients within two years.

Retinal implants are able to partially restore the vision of people with particular

forms of blindness caused by diseases such as macular degeneration or retinitis

pigmentosa. About 1.5 million people worldwide have retinitis pigmentosa, and one in 10

people over the age of 55 have age related macular degeneration. The invention andimplementation of artificial eye could help those people.

But whatever be the pro and cons of this system, if this system is fully developed

it will change the lives of millions of people around the world. We may not restore the

vision fully, but we can help them to least be able to find their way, recognize faces, read

books, above all lead an independent life.


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REFERENCES

[1] Bionic Eye: What does the future hold by Jack Kerouac.

[2] A Bionic Eye comes to market by Kurzweil Al.

WEB REFERENCES

[1]www.spectrum.ieee.org

[2]www.stanford.edu

[3]www.bionicvision.org.au

[4]www.visionaustralia.org

[5] www.wikipedia.org
http://www.spectrum.ieee.org/http://www.spectrum.ieee.org/http://www.spectrum.ieee.org/http://www.stanford.edu/http://www.stanford.edu/http://www.stanford.edu/http://www.bionicvision.org.au/http://www.bionicvision.org.au/http://www.bionicvision.org.au/http://www.visionaustralia.org/http://www.visionaustralia.org/http://www.visionaustralia.org/http://www.visionaustralia.org/http://www.bionicvision.org.au/http://www.stanford.edu/http://www.spectrum.ieee.org/

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