WELCOME

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OUTLINEINTRODUCTIONNATURAL EYE Basic structure Working ARTIFICIAL EYE ASR chip Implantation of ASR chip Components of artificial eye Video camera in eye glasses Fibre optic element Detector element CouplerWORKING OF ARTIFICIAL EYE RETINAL STIMULATIONADVANTAGES AND DISADVANTAGESCONCLUSIONREFERENCES 3

INTRODUCTIONTwenty five million people worldwide are

blind because one layer of cells on their retinas no longer works. By 2020,this figure is expected to double. Using information technology , researches are developing an artificial retina. Their efforts yielding results. For example, with the help of an experimental artificial retina, a man who has been blind for 50 years is now able to see.

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NATURAL EYEAn eye is an organ of vision that detects light.Main parts are Cornea, Iris, Retina, Lens,

Pupil.The conjunctiva is a clear membrane

covering the white of eye.The lens helps to focus light on retina.The optic nerve conducts visual impulses to

the brain from the retina.

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Natural eye

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WORKING OF NATURAL EYEThe light rays enter the eye through the

cornea.Then move through pupil, crystalline lens,

vitreous humour and finally fall on the retina.Retina processes and converts incident light

to neuron signals using special pigments in rod and cone cells.

These neuron signals are transmitted through the optic nerve.

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WORKING….The neuron signals move through the visual

pathway: Optic nerve-optic chiasm-optic tract-optic radiations-Cortex.

The neuron signals reach the visual cortex and its radiations for the brain`s processing.

The visual cortex interprets the signals as images and along with other parts of brain , interpret the images to extract form, meaning, memory and context of the images

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ASR CHIPASR chip is made of silicon and is enclosed in

plastic material known as PMMA.The ASR microchip is powered by incident

light and does not require the use of external wires or batteries.

The microsurgical procedure consists of a standard ophthalmic operation called a vitrectomy and retinotomy, plus the implantation of the chip, itself.

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IMPLANTATION OF ASR CHIPThe surgeon starts by making three tiny

incisions in the white part of the subject’s eyeThrough these incisions ,the surgeon

replaces the vitreous gel in the middle of the eye with saline.

Makes an opening in the retina through which fluid is injected: the fluid lifts up a portion of the retina from the back of the eye.

Create a small pocket in the subretinal space just wide enough to accommodate the ASR microchip

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The surgeon then slides the implant into the subretinal space

Then he introduces air into the middle of the eye to gently push the retina back down over the implant

Over a period of one or two weeks ,the air bubble is reabsorbed and replaced by fluids created within the eye

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ASR chip in sub retinal space14

COMPONENTS OF ARTIFICIAL EYEVideo camera in eye glassesFiber-optic elementDetector elementCoupler

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VIDEO CAMERA IN EYE GLASSESVisual signals are captured by a small video

camera in the eye glasses of the blind person using a charge coupled (CCD) sensor

The CCD sensor digitises the visual image intercepted by the camera

The digital representations of the images are then beamed via laser pulses into a microchip and processed through a microcomputer worn on a belt

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CHARGE COUPLED DEVICE(CCD)CCD is an image sensor, consisting of an

integrated circuit containing an array of linked, or coupled , capacitors sensitive to light

Under the control of an external circuit , each capacitor can transfer its charge to one or other neighbors

The photoactive region of the CCD is, an epitaxial layer of silicon

It has a doping of p+ (Boron) and is grown upon the substrate material , often p++

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FIBRE-OPTIC ELEMENTFor directing incoming visible light of a

particular intensity to detector elementA micro lens is placed in front of the fibre-

optic element to focus incoming light into the fibre-optic element

A coloured filter is placed in front of the micro lens to pass light corresponding to a particular colour to the micro lens

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Consist of a glass core,sourrounded by a glass “optical cladding” giving an outside dia about 120micrometers

The cladding keeps the value of critical angle constant throughout the whole length of the fibre

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DETECTOR ELEMENTThe detector used is a micro photodiode.Light of sufficient photon energy strikes the

diode , it excites an electron and a positively charged electron hole

The micro photodiodes convert the light energy from images into electro chemical impulses that stimulate the remaining functional cells of the retina in patients

The detector element is a photodiode which emits an output signal as a function of intensity of incoming signal

The output of detector is fed to the coupler20

COUPLERThe coupler is used to couple the output of

detector to the optic nerveIt used a scanning tunnelling microscope

(STM) tipThe STM tip receives an electrical signal

from the photodiode and transmits an electrical signal to the retinal nerves

STM tips are basically metal wires that are finely sharpened at one end

This end is coupled to the photodiode , while the sharpened end is directed towards the retina for releasing current at specific point on the retina 21

WORKING OF ARTIFICIAL EYEVisual signals are captured by a small video

camera in the eyeglasses of the blind person using a charge coupled device(CCD) sensor

The CCD sensor digitises the visual images intercepted by the camera

The digital representations of the images are then beamed via laser pulses into a microchip implanted in the eye and processed through a microcomputer worn on a belt

The signals are transmitted to the electrode array in the eye

The array stimulates optical nerves, which the carry a signal to the brain

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RETINAL STIMULATIONTo ways of retinal stimulationThey are sub-retinal stimulation and epi-

retinal stimulationSub retinal approach involves the electrical

stimulation of inner retina from the sub retinal space by implantation of a semiconductor based micro photodiode array(MPA) into this location.

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.

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SUB-RETINAL VS EPI-RETINAL STIMULATIONFixing a electrode array is easier with sub-

retinal stimulation than epiretinal stimulation.

Sub retinal stimulation intact optics whereas epiretinal stimulation does not.

Sub retinal stimulation is a lot of more electrical power that epiretinal stimulation

Sub retinal stimulation can used retinals circuitry. epiretinal stimulation requires the processing of visual information into specific patterns for stimulation of retinal ganglion cells.

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ADVANTAGESASR microchip can restore eye sight for

millions of blind people.If the future artificial retinas can be made

from thin films that can shift their molecular configurations on-the-fly, it may be possible to even configure the retinas to look at different parts of the light specific as well.

The silicon retina can also be used in cameras for remote monitoring for safety, identification purpose.

The researchers have built a prototype that contains 256 pixels, and are working to make a more complete silicon-based system that can be used in autonomous robot and smart sensors.

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DISADVANTAGESThere is risk of retinal damage at

implantation.The video cameras and complicated image

processing software that are used to give machines the ability to see are relatively bulky and expensive.

The silicon retina provides information about the edges of image rather than a whole picture.

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CONCLUSIONArtificial eye will be a wonderful boon that

will restore eyesight for millions of blind people. Obviously, the first users of artificial retina technology will be blind people. Once the resolution of an artificial retina exceeds that of the human eye and it becomes possible to combine it with zoom capability, artificial eye implants will also become attractive for people with perfectly healthy eyes.

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REFERENCES“Towards artificial eye” a paper presented by

Dagnelie G. Massof ,Johns Hopkins Univ.Sch.of med., Baltimore, MD appeared in IEEE Spectrum,May 1996,volume 33,issue 5.

“E-eye: For the blind and beyond” Electronics for you magazine, September 2006.

Reni Jogi, (2004),”Basic Opthalmology”by, Jaypee Publications, Edition 3,New Delhi.

“The Artificial Silicon Retina(ASR) microchip for the treatment of retinitis Pigmentosa”by Alan Y. Chow, MD; Vincent Y.Chow,BS, April 2004. 28