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INTRODUCTION

A Bionic Eye is a device, which acts as an artificial eye. It is a broad term for the entire electronics system consisting of the image sensors, processors, radio transmitters & receivers, and the retinal chip. Based on the institute developed these devices are developed but with minor to major differences, of these the devices with functional capability and those which are clinically tested and results proved are discussed here.Here the designer’s objective is to go for a system that is technically perfect with no loop holes and that is harmless to the human body which receives the system and that is commercially viable both in terms of ease of manufacture, cost and the process of implanting.

Blindness means loss of vision. Rods and Cones, millions of them are in the back of every healthy human eye. They are biological solar cells in the retina that convert light to electrical impulses -- impulses that travel along the optic nerve to the brain where images are formed. Without them, eyes lose the capacity to see, and are declared blind. Degenerative retinal diseases result in death of photoreceptors--rod-shaped cells at the retina's periphery responsible for night vision and cone-shaped cells at its center responsible for color vision. Worldwide, 1.5 million people suffer from Retinitis Pigmentosa (RP), the leading cause of inherited blindness. In the Western world, Age Related Macular Degeneration (AMD) is the major cause of vision loss in people over age 65, and the issue is becoming more critical as the population ages. Each year, 700,000 people are diagnosed with AMD, with 10 percent becoming legally blind, defined by 20/400 vision. Many AMD patients retain some degree of peripheral vision.

Currently, there is no effective treatment for most patients with AMD and RP, the researchers say . However, if one could bypass the photoreceptors and directly stimulate the inner retina with visual signals, one might be able to restore some degree of sight.

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CAUSES OF BLINDNESSThere are two important types of retinal degenerative disease:

Retinitis pigmentosa (RP), and 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 retina’s 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.

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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 retina’s 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 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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BIONIC EYE: TWO APPROACHES

There are two approaches by which we can implant a bionic eye:

Artificial Silicon Retina – ASR Multi-unit Artificial Retina Chipset - MARC

aRTIFICIAL SILICON RETINA(ASR)

The ASR is a silicon chip 2 mm in diameter and 1/1000 inch in

thickness. It contains approximately 3,500 microscopic solar cells called

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"micro photodiodes," each having its own

stimulating electrode. These micro photodiodes are

designed to convert the light energy from images

into thousands of tiny electrical impulses to

stimulate the remaining functional cells of the retina in patients suffering

with AMD and RP types of conditions.

The ASR is powered solely by incident light and does not require the

use of external wires or batteries. When surgically implanted under the

retina, in a location known as the sub retinal space, the ASR is designed to

produce visual signals similar to those produced by the photoreceptor layer.

From their sub retinal location these artificial "photoelectric" signals from

the ASR are in a position to induce biological visual signals in the remaining

functional retinal cells which may be processed and sent via the optic nerve

to the brain.

MULTIPLE UNIT ARTIFICIAL RETINA CHIPSET (MARC)

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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.

The schematic of the components of the MARC to be implanted 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, an example of which is given in the figure below, 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 through the electrodes in a manner that corresponds to the image acquired by the CMOS Camera.

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WORKING

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 retina’s 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

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1000 electrodes on the retinal implant, which they believe could allow for reading, facial recognition capabilities etc.

1: Camera on glasses views image2: Signals are sent to hand-held device3: Processed information is sent back to glasses and wirelessly transmitted to receiver under surface of eye4: Receiver sends information to electrodes in retinal implant5: Electrodes stimulate retina to send information to brain.

The MARC system, pictured in the figures will operate in the following manner. An external camera will acquire an image, whereupon it will be

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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 patient’s retina.

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

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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 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.

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

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FACTS ABOUT BIONIC EYE

Scientists at the Space Vacuum Epitaxy Centre (SVEC) based at the

University of Houston, Texas, are using a new material, comprising tiny

ceramic photocells that could detect incoming light and repair

malfunctioning human eyes. Scientists at SVEC are conducting preliminary

tests on the biocompatibility of this ceramic detector. The artificial retinas

constructed at SVEC consist of 100,000 tiny ceramic detectors, each 1/20th

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the size of a human hair. The assemblage is so small that surgeons can’t

safely handle it. So, the arrays are attached to a polymer film one millimeter

in size. After insertion into an eyeball, the polymer film will simply dissolve

leaving only the array behind after a couple of weeks.

THE ANALOGY

There is a great degree of coherence between the ways our eyes

function to that of a change over time as the respective camera. Perhaps –

our eyes had been the technologies are further developed and inspiration

behind the camera’s invention.

From the structural point of view the eye may be compared with a

camera. The eyelids act as a shutter and there is an entrance – the cornea; a

diaphragm to regulate aperture and therefore the amount of light entering –

the iris; a lens to focus the image;

ADVANTAGES OF MARC SYSTEM

Compact Size – 6x6 mm Diagnostic Capability Reduction of stress upon retina

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Heat dissipation problems are kept to a minimum

Although the device will not be able to restore the eye sight of the

entire blind community, researchers are certain many people will benefit

from the technology. For instance, age-related macular generation is the

leading cause of blindness in the industrialized world, with about 2 million

Americans currently suffering from the condition. The new technology will

hopefully assist people suffering from this condition, and individuals

suffering from retinitis pigmentosa (a genetic condition), but will not help

glaucoma patients. The researchers note the device has some limitations,

and it will not restore perfect vision. However, they are sure it will give

people the advantage of having a general sense of their surroundings.

Hopefully, the technology may enable people to recognize faces and facial

expressions. "The thing is to significantly improve the quality of life for blind

patients," said Joseph Rizzo of the Massachusetts Eye and Ear Infirmary, who

has co-directed the project with MIT's John Wyatt since 1988.

CHALLENGES

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One of the greatest challenges seems to be ensuring that the implant can remain in the eye for decades or more without causing scarring, immune system responses, and general degradation from daily biological wear and

tear. Current retinal implants provide very low resolution-- just a few

hundred pixels.

There are many doubts as to how the brain will react to foreign signals generated by artificial light sensors. These artificial retinas are still years away from becoming widespread because they are too expensive, too clunky, and too fragile to withstand decades of normal wear and tear.

A Nano-sized irritant can create havoc in the eye. There are 120 million rods and 6 million cones in the retina of every

healthy human eye. Creating an artificial replacement for these is no easy task.

Si based photo detectors have been tried in earlier attempts. But Si is toxic to the human body and reacts unfavourably with fluids in the eye.

There are many doubts as to how the brain will react to foreign signals generated by artificial light sensors.

On going developments Argus – iii the artificial retina

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Fig. Argus III implant

Funded by the US Department of Energy and lead by Lawrence Livermore National Labs, Argus seeks to create epiretinal prosthesis, a device that will take the image from a camera and send it to your brain via your optic nerve. The first two phases of Argus (which we call Argus I and Argus II) have had extraordinary success with implants in more than 30 patients. Now, LLNL is getting ready to launch Argus III – the third phase that will expand the number of patients, the quality of vision provided, and ease in which the device is implanted.

There is other epiretinal prosthesis in development. The one at MIT is particularly promising. Yet Argus is at the forefront of the field.The Argus III will work by taking the image from a camera and wirelessly transmitting it to an electronics package. That package will stimulate undamaged retinal tissue using a thin film transistor electrode array. In Argus I, it took patients about 15 seconds to recognize objects using the retinal implant. In Argus II that was down to 2-3 seconds. Argus I had implants that provided 16 pixels of resolution. Argus II got up to 60, enough for the edges of doors, or the shape of a building. According to images from the LLNL site, the current implants prepared for Argus III will have 200+ pixels. The DOE eventually wants 1000 pixels; at that point you could reliably make out someone’s face.

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Fig. Transistor electrode array for the Argus III.

Improving the pixel count isn’t easy as it depends on the number of electrodes that get attached to the retina. The Argus device works by taking a thin-film electrode array and surgically implanting it onto the retinal tissue.

These electrodes communicate wirelessly with an external camera through a biocompatible electronics package that is attached to the array. The entire assembly is smaller than it sounds and fits within the ocular cavity. Increasing the resolution of Argus means placing more electrodes on that array, as well as developing the electronics package that can handle the signal and processing.

CONCLUSION

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Revolutionary piece of technology has the potential to change people's lives.

Artificial Eye is such a revolution in medical science field.

A bionic eye implant that could help restore the sight of millions of blind people could be available to patients within two years.

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 and implementation of artificial eye could help those people.

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

ReferenceS

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www.spectrum.ieee.org

www.stanford.edu

www.bionicvision.org.au

www.visionaustralia.org

www.2-sight.com

www.cosmosmagazine.com

www.ngm.nationalgeographic.com

www.sessionmagazine.com

www.health.howstuffworks.com

www.wikipedia.org