Download - Bionic-eye Org PPT
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BIONIC EYE
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 PIGMENTOSA Caused by the breakdown in the function of
rods &cones
b.MACULAR DEGENERATION Retinal Pigment Epithelium gradually wears out
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 Processing
The CMOS Image Sensor
•Cost Effective for IC’s
•Low Power, less volume
•Easily mounted on a pair of glasses
Video Processing
• Implemented using SRAM Frame buffers, ADC & a FPGA/ CPLD
•Reconfigurable FPGA’s allow flexibility for various Image Processing Algorithms including Artificial Neural Networks
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ASK-PWM Encoding
Alternate Mark Inversion
•Each pulse encodes 1 bit of data
•0’s represented by 50% duty cycle pulses
•1’s represented by pulses with alternating larger or smaller duty cycles (75% & 25% respectively) symmetric around 50%
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Class-E Power Amplifier
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.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
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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
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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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Current Controller and Stimulator
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 gray-scale stimulus
Thus each of the 100 electrodes are exited by different currents which form the desired image pattern
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Typical Image Formation
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MARC-3 Chips
The Electrode Array Photograph of MARC-3 Chip
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Important Aspects
Field 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.
REVIEW
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The Resolution Challenge
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Artificial Silicon Retina: The Second Approach
The ASR is a silicon chip2 mm in diameter and 1/1000 inch in thickness.
It contains approximately3,500 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 eye
Eliminates use of power supplies
Epiretinal 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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Approaches Towards Retinal Prosthetic Implantation
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 Images
The 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.
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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