27-07-2011, 09:43 AM
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BIONIC EYE
A Look into Current Research and Future Prospects
Blindness
Inability to see
Causes of Blindness
Damage to:
Clear Structures in the eye, that allow the light to pass through
The nerves within the eye
Optic Nerve
Brain
Bradley’s Research
Breakthrough in 1960
First electrical stimulation of Visual Cortex
Bright spots called phosphenes produced
Why we should be optimistic?
The Success of :
Cardiac pacemakers as neural prosthesis
Cochlear implants to restore hearing to the deaf
Rapid developments in :
VLSI design
Micro- fabrication technology
Overview
Biology of the Eye
MIT – Harvard Device
ASR – Artificial Silicon Retina
MARC – Multiple Unit Artificial Retina Chip Set System
BIONIC EYE ?
Bio-electronic eye
Electronic device which replaces functionality of a part or whole of the eye
Used for replacing functionality (or)
Adding functionality to the eye
Structure of the Eye
The Retina
The Eye with Retina
Diseases of the Eye
Retinitis Pigmentosa
Macular Degeneration
Retinitis Pigmentosa
Hereditary Genetic Disease
Peripheral Rods degenerate
Gradually progresses towards center of eye
Spares the foveal region
Tunnel vision results
Macular Degeration
Genetically Related
Cones in Macula region degenrate
Loss or damage of central vision
Peripheral Retina spared
Common among old people
Retinitis Pigmentosa ( Opthalmoscope View )
Macular Degeneration (Opthalmoscope View)
Regions of Implantation
Retina
Optic Nerve
Lateral geniculate body
Visual Cortex
MIT-Harvard device
Features
Epi-Retinal Approach
Microelectrode array replaces damaged photoreceptors
Power source – Laser(820nm wavelength)
Image Acquisition - Using CCD Camera
Patient spectacle holds the camera and power source
Site of Implant
Implant Structure
Layers
1- Photodiode Array
2- Polyimide strip
3- Stimulator chip
Electrodes on other end of Polyimide strip
Working of the System - 1
CCD camera input – External light intensity
CCD output amplitude-modulates laser source
This hits photodiode array of implant
This in turn powers stimulator chip (SC)
Working of the System - 2
SC drives current to electrodes facing retina
This excites the ganglionic cells > axons > optic nerve > visual cortex in occipital lobe of brain
Brain helps in perceiving an image
The Whole Picture
Advantages
Very Early in the visual pathway
No Batteries implanted within body
No complicated surgical procedure
Power Requirement – ¼ of milliwatt
Disadvantages
Axons b/w electrodes and ganglionic cells
Other axons get excited – unwanted perception of large blur
Extra circuitry required for downstream electrical input
Artificial Retina Prosthesis using ASR (Artificial Silicon Retina)
The Eye
Human Eye is similar to a camera
Macula provides the highest
resolution of the image which
we see.
Macula is comprised of multiple
layers of cells which process
the initial “analog”light energy
entering the eye into “digital”
electrochemical impulses.
Human eye has nearly
100 million photoreceptors
Need for ASR
Retinitis Pigmentosa(RP) and Age related Macular degeneration (ARMD)
are Progressive blinding disorders of the outer retina which involve degeneration of the neurons.
There are no proven effective therapeutic remedy for these disorders .
Some of Methods employed to slow or halt the disease time course are
Use of Intravitreal injection of certain growth factors.
Identification of specific gene mutations has led to the development of the gene therapy approaches.
Transplantation can be effective in rescuing the photoreceptors
from degeneration.
Need for ASR
The first two methods are promising for treating patients early in the course of the degenerative process, they are of relatively modest value for the patients in whom the photoreceptors have already degenerated.
Besides the Genetic and the Anatomic approach , there is an need to find an alternative approach.
Fundamental idea behind ASR
ASR is a solid state biocompatible chip which contains an array of photo receptors ,and is implanted to replace the functionality of the defective photoreceptors .
Current generated by the device in response to light stimulation will alter the membrane potential of the overlying neurons and thereby activate the visual system.
Visual sensations or “phosphenes” can be evoked by electrical stimulation of the different levels of the visual pathway.
Phosphenes are evoked by the stimulation of the eyeball or the visual cortex.
Artificial vision created by the controlled electric stimulation of the retina has color.
Approaches Towards Retinal Prosthetic Implantation
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.
Enhancement of the image quality using the ASR
Limitations Of ASR’s
ASR is designed to interface and function with the retina that has partial outer retinal degeneration.
ASR can be applied only when the photoreceptor cellular layer of the retina is damaged but the remaining cellular layers are still functional.
ASR can be effectively applied to RP and AMD.
Conditions amenable to treatment with ASR’s include some forms of long-term retinal detachment,Usher’s syndrome, Cone- Rod Dystrophy.
Sub-Retinal Approach
The basic idea-”Alter the membrane potential”
IMPLANT DESIGN
Primitive devices
Single photosensitive pixel(3mm in diameter)
Neo devices
The current micro photodiode array (MPA) is comprised of a regular array of individual photodiode subunits, each approximately 20×20-µm square and separated by 10-µm channel stops (37). The resulting micro photodiode density is approximately 1,100/m2.
IMPLANT features
The size has decreased from 250um to 50um
No external power supply
500nm to 1100nm wavelength response
MANUFACTURING PROCESS
Implants are comprised of a doped and ion-implanted silicon substrate disk to produce a PiN (positive-intrinsic-negative) junction. Fabrication begins with a 7.6-cm diameter semiconductor grade N-type silicon wafer.
For the MPA device, a photomask is used to ion-implant shallow P+ doped wells into the front surface of the wafer, separated by channel stops in a pattern of individual micro photodiodes. An intrinsic layer automatically forms at the boundary between the P+-doped wells and the N-type substrate of the wafer.
Micro photodiodes
PROCESS (Contd.)
The back of the wafer is then ion-implanted to produce a N+ surface. Thereafter, an insulating layer of silicon nitrate is deposited on the front of the wafer, covering the entire surface except for the well openings.
A thin adhesion layer, of chromium or titanium, is then deposited over the P+ and N+ layers. A transparent electrode layer of gold, iridium/iridium oxide, or platinum, is deposited on the front well side, and on the back ground side.
In its simplest form, the photodiode and electrode layers are the same size. However, the current density available at each individual micro photodiode subunit can be increased by increasing the photodiode collector to electrode area ratio.
Post Implant function and Inference
Measurement procedure
IR stimulation at 940nm on the ASR chip
Recorded at the corneal surface using contact lens electrode
Comparison of responses of gold, platinum and iridium electrodes
Iridium based device has a longer persistence
Stability of these electrodes
ASR implanted into the eye
BIO-COMPATIBILTY results
The good news
There is no progressive change in retinal appearance that may be associated with retinal toxicity.
How do we know? ----”ERG and Ganzfeld stimulus has an answer”
The Bad news
Loss of photoreceptive layer over the region of implant which is expected due to deprival of oxygen and nutrients to those cells underlying the chip.
Conclusion
Its been 40 years since Arne Larsson received the first fully implanted cardiac pacemaker at the Karolinska Institute in Stockholm.
Researchers throughout the world have looked for ways to improve people's lives with artificial, bionic devices.
Bionic devices are being developed to do more than replace defective parts.
Researchers are also using them to fight illnesses.
Providing power to run bionic implants and making connections to the brain's control system pose the two great challenges for biomedical engineering.
We are now looking at devices like bionic arms, tongues, noses etc.
BIONIC EYE
A Look into Current Research and Future Prospects
Blindness
Inability to see
Causes of Blindness
Damage to:
Clear Structures in the eye, that allow the light to pass through
The nerves within the eye
Optic Nerve
Brain
Bradley’s Research
Breakthrough in 1960
First electrical stimulation of Visual Cortex
Bright spots called phosphenes produced
Why we should be optimistic?
The Success of :
Cardiac pacemakers as neural prosthesis
Cochlear implants to restore hearing to the deaf
Rapid developments in :
VLSI design
Micro- fabrication technology
Overview
Biology of the Eye
MIT – Harvard Device
ASR – Artificial Silicon Retina
MARC – Multiple Unit Artificial Retina Chip Set System
BIONIC EYE ?
Bio-electronic eye
Electronic device which replaces functionality of a part or whole of the eye
Used for replacing functionality (or)
Adding functionality to the eye
Structure of the Eye
The Retina
The Eye with Retina
Diseases of the Eye
Retinitis Pigmentosa
Macular Degeneration
Retinitis Pigmentosa
Hereditary Genetic Disease
Peripheral Rods degenerate
Gradually progresses towards center of eye
Spares the foveal region
Tunnel vision results
Macular Degeration
Genetically Related
Cones in Macula region degenrate
Loss or damage of central vision
Peripheral Retina spared
Common among old people
Retinitis Pigmentosa ( Opthalmoscope View )
Macular Degeneration (Opthalmoscope View)
Regions of Implantation
Retina
Optic Nerve
Lateral geniculate body
Visual Cortex
MIT-Harvard device
Features
Epi-Retinal Approach
Microelectrode array replaces damaged photoreceptors
Power source – Laser(820nm wavelength)
Image Acquisition - Using CCD Camera
Patient spectacle holds the camera and power source
Site of Implant
Implant Structure
Layers
1- Photodiode Array
2- Polyimide strip
3- Stimulator chip
Electrodes on other end of Polyimide strip
Working of the System - 1
CCD camera input – External light intensity
CCD output amplitude-modulates laser source
This hits photodiode array of implant
This in turn powers stimulator chip (SC)
Working of the System - 2
SC drives current to electrodes facing retina
This excites the ganglionic cells > axons > optic nerve > visual cortex in occipital lobe of brain
Brain helps in perceiving an image
The Whole Picture
Advantages
Very Early in the visual pathway
No Batteries implanted within body
No complicated surgical procedure
Power Requirement – ¼ of milliwatt
Disadvantages
Axons b/w electrodes and ganglionic cells
Other axons get excited – unwanted perception of large blur
Extra circuitry required for downstream electrical input
Artificial Retina Prosthesis using ASR (Artificial Silicon Retina)
The Eye
Human Eye is similar to a camera
Macula provides the highest
resolution of the image which
we see.
Macula is comprised of multiple
layers of cells which process
the initial “analog”light energy
entering the eye into “digital”
electrochemical impulses.
Human eye has nearly
100 million photoreceptors
Need for ASR
Retinitis Pigmentosa(RP) and Age related Macular degeneration (ARMD)
are Progressive blinding disorders of the outer retina which involve degeneration of the neurons.
There are no proven effective therapeutic remedy for these disorders .
Some of Methods employed to slow or halt the disease time course are
Use of Intravitreal injection of certain growth factors.
Identification of specific gene mutations has led to the development of the gene therapy approaches.
Transplantation can be effective in rescuing the photoreceptors
from degeneration.
Need for ASR
The first two methods are promising for treating patients early in the course of the degenerative process, they are of relatively modest value for the patients in whom the photoreceptors have already degenerated.
Besides the Genetic and the Anatomic approach , there is an need to find an alternative approach.
Fundamental idea behind ASR
ASR is a solid state biocompatible chip which contains an array of photo receptors ,and is implanted to replace the functionality of the defective photoreceptors .
Current generated by the device in response to light stimulation will alter the membrane potential of the overlying neurons and thereby activate the visual system.
Visual sensations or “phosphenes” can be evoked by electrical stimulation of the different levels of the visual pathway.
Phosphenes are evoked by the stimulation of the eyeball or the visual cortex.
Artificial vision created by the controlled electric stimulation of the retina has color.
Approaches Towards Retinal Prosthetic Implantation
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.
Enhancement of the image quality using the ASR
Limitations Of ASR’s
ASR is designed to interface and function with the retina that has partial outer retinal degeneration.
ASR can be applied only when the photoreceptor cellular layer of the retina is damaged but the remaining cellular layers are still functional.
ASR can be effectively applied to RP and AMD.
Conditions amenable to treatment with ASR’s include some forms of long-term retinal detachment,Usher’s syndrome, Cone- Rod Dystrophy.
Sub-Retinal Approach
The basic idea-”Alter the membrane potential”
IMPLANT DESIGN
Primitive devices
Single photosensitive pixel(3mm in diameter)
Neo devices
The current micro photodiode array (MPA) is comprised of a regular array of individual photodiode subunits, each approximately 20×20-µm square and separated by 10-µm channel stops (37). The resulting micro photodiode density is approximately 1,100/m2.
IMPLANT features
The size has decreased from 250um to 50um
No external power supply
500nm to 1100nm wavelength response
MANUFACTURING PROCESS
Implants are comprised of a doped and ion-implanted silicon substrate disk to produce a PiN (positive-intrinsic-negative) junction. Fabrication begins with a 7.6-cm diameter semiconductor grade N-type silicon wafer.
For the MPA device, a photomask is used to ion-implant shallow P+ doped wells into the front surface of the wafer, separated by channel stops in a pattern of individual micro photodiodes. An intrinsic layer automatically forms at the boundary between the P+-doped wells and the N-type substrate of the wafer.
Micro photodiodes
PROCESS (Contd.)
The back of the wafer is then ion-implanted to produce a N+ surface. Thereafter, an insulating layer of silicon nitrate is deposited on the front of the wafer, covering the entire surface except for the well openings.
A thin adhesion layer, of chromium or titanium, is then deposited over the P+ and N+ layers. A transparent electrode layer of gold, iridium/iridium oxide, or platinum, is deposited on the front well side, and on the back ground side.
In its simplest form, the photodiode and electrode layers are the same size. However, the current density available at each individual micro photodiode subunit can be increased by increasing the photodiode collector to electrode area ratio.
Post Implant function and Inference
Measurement procedure
IR stimulation at 940nm on the ASR chip
Recorded at the corneal surface using contact lens electrode
Comparison of responses of gold, platinum and iridium electrodes
Iridium based device has a longer persistence
Stability of these electrodes
ASR implanted into the eye
BIO-COMPATIBILTY results
The good news
There is no progressive change in retinal appearance that may be associated with retinal toxicity.
How do we know? ----”ERG and Ganzfeld stimulus has an answer”
The Bad news
Loss of photoreceptive layer over the region of implant which is expected due to deprival of oxygen and nutrients to those cells underlying the chip.
Conclusion
Its been 40 years since Arne Larsson received the first fully implanted cardiac pacemaker at the Karolinska Institute in Stockholm.
Researchers throughout the world have looked for ways to improve people's lives with artificial, bionic devices.
Bionic devices are being developed to do more than replace defective parts.
Researchers are also using them to fight illnesses.
Providing power to run bionic implants and making connections to the brain's control system pose the two great challenges for biomedical engineering.
We are now looking at devices like bionic arms, tongues, noses etc.
