BIONIC EYE

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Overview

Human eye Eye defects History Bonic eye-2 approaches MARC MARC System Functionality ASR Retinal Implants Advantages & Disadvantages Future Scopes

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Human Eye

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Eye Defects .a.RETINIS PIGMENTOSACaused by the breakdown in the function of rods &cones

b.MACULAR DEGENERATIONRetinal Pigment Epithelium gradually wears out

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HISTORY

Why bionic eye?.No proven effective remedy for these disorders . In 1988 ,Dr.Humayun proved that the nerves behind the retina still function even when the retina degenerated .1990-ArgusII ,bionic eye was developed by U.S company Second Sight

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Bionic Eye:Two Approaches

MARC-Multiple Unit Artificial Retina Chipset ASR-Artificial Silicon Retina

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Multiple Unit Artificial Retina Chipset (MARC) The Concept

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MARC System Functionality

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Extra-Ocular CMOS Camera & Video ProcessingThe CMOS Image Sensor Cost Effective for ICs Low Power, less volume Easily mounted on a pair of glasses

Video Processing Implemented using SRAM Frame buffers, ADC & a FPGA/ CPLD Reconfigurable FPGAs allow flexibility for various Image Processing Algorithms including Artificial Neural Networks

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Back

ASK-PWM EncodingAlternate Mark Inversion Each pulse encodes 1 bit of data 0s represented by 50% duty cycle pulses 1s represented by pulses with alternating larger or smaller duty cycles (75% & 25% respectively) symmetric around 50%Back

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Class-E Power Amplifier.The class E amplifier is a highly efficient switching power amplifier, typically used at such high frequencies that the switching time becomes comparable to the duty time .The whole circuit performs a damped oscillation. .With load, frequency, and duty cycle (0.5) as given parameters the four parameters (L,L0,C,C0) are determined. Back 11

RF Telemetry

An Inductive Link consists of 2 resonant circuits Mutual Inductance M plays a vital role, Maximizing it is very important As the MARC transmits information via AM/ASK, fluctuations in the coupling constant could potentially be perceived as information by the processing chips Primary coil is driven with 0.5-10MHz signal for Power accompanied by a 10KHz ASK signal which provides data It is suitably recovered at the receiving end

Back

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Data, Clock & Power Recovery

Data & Clock Recovery The low frequency data signal is obtained by a Low Pass filtering The first RF signal conveys the configuration data which sets the pulse width, height and period Then the actual Image is transmitted ASK demodulator obtains the PWM scheme. Delay Locked Loop (DLL) deciphers the PWM wave to obtain the Data transmitted Clock is defined as the rising edge of the pulse & no explicit clock recovery circuits are required

Power Recovery The high frequency RF carrier envelope is obtained by filtering the output of receiver coil The sinusoidal signal is then amplified to suitable levels and then rectified Rectification provides the required DC voltage power

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Back

Current Controller and Stimulator

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20 controlled variable current (CVCS) sources are designed for retinal simulation Each receive clocking & data info from deciphered PWM wave Each CVCS is connected to 5 electrodes through a DEMUX Each current source provides sixteen level (4 bit) linear grayscale stimulus Thus each of the 100 electrodes are exited by different currents which form the desired image pattern Back

Typical Image Formation

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MARC-3 Chips

The Electrode Array

Photograph of MARC-3 Chip

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Important AspectsField of View More the number of Ganglion cells stimulated, more is the field of view Thus large electrodes and the area becomes a trade-off Changing Scene and Real-time vision The whole process must happen extremely fast so that patients see in real time This is important as any noticeable lag could stimulate the "vestibular-ocular reflex", making people feel dizzy and sick.

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REVIEW

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The Resolution Challenge

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Artificial Silicon Retina: The Second Approach

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 "microphotodiodes, each having its own stimulating electrode. These microphotodiodes are designed to convert the light energy from images into thousands of tiny electrical impulses

Adv: Receives power from light entering the eyeEliminates use of power supplies

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Approaches Towards Retinal Prosthetic ImplantationEpiretinal Approach involves a semiconductor based device positioned on the surface of the retina to try to simulate the remaining overlying cells of the retina.

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

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Subretinal Implant

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Artifical Retina Component Chip(ARCC)

.02mm thick very small device Placed b/w layers of retina. A secondary device attached to a pair of eyeglasses directs a laser at the chip's solar cells to provide power. The laser would have to be powered by a small battery pack. According to researchers, the ARCC will give blind patients the ability to see 10 by 10 pixel images.

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The ImagesThe top image shows the raw output of the retina chip.

The middle one a picture processed from it.

The third shows how a moving face would appear.

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Advantages

Assit people suffering from RP&AMD

Quite durable last for atleast 10yrs inside eye. Easy surgical methods involved Small component size Reduction of stress upon the retina

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Disadvantages

Donot restore perfect vision but gives sense of surroundings Only effective for people who once had sight Optic nerves should be functional atleast partiallly Cost around $30,000

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Future scopes

Face recognition use of 1000 electrodes Bionic eye to work beyond capability of human eye. Detect X-ray,infrared,night vsion. Reduced cost Run software algorithms

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References

E.D. Juan, Jr. M. S. Humayun, H. D. Phillips; Retinal Microstimulation, M. Humayun, Is Surface Electrical Stimulation of the Retina a Feasible Approach Towards The Development of a Visual Prosthesis? Phillips, Visual Perception Elicited by Electrical Stimulation of Retina in Blind Humans by Electrical Stimulation of Retina in Blind Humans, Arch. Ophthalmol, pp. 40-46, vol. 114, Jan. 1996. W. Liu, E. McGucken, K. Vichiechom, M. Clements, E. De Juan, and M. Humayun, Dual Unit Retinal Prosthesis, IEEE EMBS97. Mueller, M. Humayun, E. de Juan, An Implantable Neuro-stimulator Device for a Retinal Prosthesis, E. McGucken, Multiple Unit Artificial Retina Chipset to Benefit The Visually Impaired and Enhanced CMOS Phototransistors,

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