JAYAM COLLEGE OF ENGINEERING

AND TECHNOLOGY
NALLANUR, DHARMAPURI

ELECTRONIC-EYE: FOR THE BLIND

AND BEYOND
(USING VLSI)

Presented by,

V.JAGADESAN V.THAMOTHIRAN
shruthijagadesan@gmail.com vthamothiran1989@gmail.com

PRE –FINAL YEAR

ELECTRICAL & ELECTRONICS ENGINEERING
ABSTRACT:

Twenty five million people worldwide are blind because one layer of cells on their
retinas no longer works. By 2020, the figure is expected to double.

Using information technology, researchers are developing an artificial retina. Their

efforts have already started 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.

ARTIFICIAL RETINA: THE BASICS

An artificial silicon retina (ASR) microchip has been developed to treat vision
loss. It is a silicon chip 2 mm in diameter and 25 microns thick less than the thickness of
a human hair. It contains approximately 5000 microscopic solar cells, called ’micro
photodiodes’, each with its own stimulating electrode. these micro photodiodes convert
the light energy from images into electrochemical impulses that stimulate the remaining
functional cells of the retina in patients with age related macular degeneration and
retinitis pigmentosa types of conditions.

The ASR microchip 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’ it produces visual signals similar to those produced by
the photoreceptor layer. From their sub-retinal location, these artificial ‘photoelectric’
signals from the ASR microchip 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.
The artificial retina system comprises an array of artificial retinas, wherein each
artificial retina comprises a detector element, a fibre-optic element. For directing
incoming visible light of a particular intensity to said detector element, said detector
element emitting an output signal as a function of the intensity of the incoming visible
light, and a coupler to couple the output signal of said detector element to the retina.

The artificial retina system is preferably housed in a plastic enclosure made of a

material similar in composition to that of artificial lenses used in cataract lens
replacements.

Other advancement in the technique uses an integrated circuit (IC), which is coupled
to the photodiode of IR detector and the coupler. The IC amplifies the output signal of the
photodiode or IR detector and transmits the amplified output signal to the coupler.

A micro lens is placed in front of the fibre-optic element to focus incoming light
onto the fibre-optic element. Additionally, a color filter is placed in front of the micro
lens to pass light corresponding to particular color can be used, obviating the need to
place a color filter in front of the micro lens.
The coupler used is a scanning tunneling microscope (STM) tip. The STM tip
receives an electrical signal from the photodiode or IR detector and transmits an electrical
signal to the retinal nerves. STM tips are basically metal wires that are very finely
sharpened at one end. The tip is made of platinum. The unsharpened end of the tip is
coupled to the photodiode or IR detector while the sharpened end is directed towards the
retina for releasing current at a specific point on the retina.
Another technology uses a metal sheet instead of an STM tip. In this embodiment,
the metal sheet is disposed between the photodiode or IR detector and the retinal nerve.
The metal sheet receives the electrical signal output from the second photodiode or IR
detector and in response transmits and electrical signal to the retinal nerves. In a preferred
embodiment, the metal sheet is made of copper and has a curvature corresponding to the
curvature of the retina at the area near which the metal sheet is placed.
Visual 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 digitizes the visual
images intercepted by the camera the digital representations of the images are then
beamed via laser pulses onto 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 then carry a signal to the brain.

The first prototype implants contain 16 electrodes. The next prototype, with 50 to 100
electrodes, is in preclinical trials. The project’s ‘next generation’ device would have as
many as 100 electrodes, and researchers hope that it would allow the users to see images.

Electrical stimulation of the visual cortex causes blind subjects to perceive small
points of light, known as ‘phosphenes’. Researchers are running tests to determine the
map of the patient’s phosphenes. When electrical current zaps into the brain, lights don’t
appear only in one spot. They are spread out across space, in what artificial vision
researchers call the ‘starry-night effect.

The images that the patient sees are actually composed of a small number of white
dots that he views against his otherwise dark visual field. The arrangement of these dots
corresponds roughly to what is viewed by a small electronic pinhole camera affixed to an
eyeglass.

Organizations working on artificial retina include the blindness foundation group’s

research center at johns Hopkins University, Harvard medical school, Massachusetts
institute of technology and university of Utah, which is developing a silicon chip to be
implanted in the visual cortex of the brain.

RETINAL STIMULATION:

Two ways of stimulating the retina for artificial vision are currently well developed.
One is sub-retinal stimulation, in which a sheet containing a micro photodiode array is
inserted into the sub-retinal space to compensate for lost photoreceptor function and
stimulate the outer retinal network. The other is epi-retinal stimulation, in which retinal
ganglion cells and their axons are stimulated with a multi electrode array stimulated with
a multi electrode array attached to the vitreous side of the retina.

The researchers have built a prototype that contains 256 pixels, and are developing a
more complete silicon based system that can be used in autonomous robots and smart
sensors. They also aim at using the silicon retina in cameras for remote monitoring for
safety, identification and biometrics purposes.

SUB-RETINAL VS EPI-RETINAL STIMULATION:

1. Fixing the electrode array is easier with sub-retinal stimulation than epiretinal
stimulation.
2. Sub-retinal stimulation requires intact optics, whereas epiretinal stimulation does
not.
3. Sub-retinal stimulation needs a lot more electrical power the epiretinal
stimulation.
4. Sub-retinal stimulation can use retinal circuitry. Epiretinal stimulation requires
the processing for visual information into specific patterns for stimulation of
retinal ganglion cells.

One common drawback of both types of implants is that the implanted electrodes are
directly attached to the retina, so the risk of retinal damage at implantation is inevitable.
STILL A LONG WAY TO GO!
 The video cameras and complicated image processing software that are used to give
machines the ability to see are relatively bulky and expensive.

Since the device is not entirely implanted in the eye, it is likely to suffer the implant
must either continuously wear the eyeglasses with the camera disposed thereon or keep it
nearby for wearing when needed. It may be difficult or impractical to expect the laser
beam to reliably remain focused on the implant in the eye.

The silicon retina provides information about the edges of images rather than a whole
picture. Edge information is usually sufficient just for detecting and tracking objects.

It will take five years for the silicon retina to be available for use practically.
Applications using optical output will have to wait ten years or so until optical
interconnects are available for inter-chip communications.

When signals reach the visual cortex via the optic nerve, they influence not only the
surface of the brain but many layers of cells beneath it. The nerve again braches, the
branches branch, those branches branch and so on. In addition, every cell influences the
behavior of the cells around it, and in turn each cell is influenced by a combination of
inputs from many places.

To add to the complexity, the entire system changes many times each second.

SCOPE OF IMPROVEMENT:

The image processing approach requires the image to be captured by a sensor and
digitized. This image is then usually preprocessed to reduce noise. After these stages, an
information reduction approach can be used to provide essential environmental
information, and/or attempt to understand objects in the environment. Subjective
improvements include improved perception of brightness, contrast, color, movement,
shape, resolution and visual field size.

Scene understanding (high-level vision) is concerned with identifying features and

extracting information. The scene structure is still there to a degree, but it is idealized or
reduced. An example application might be to identify a bus stop, fire hydrant or traffic
light. It may also be useful to know the distance to the object (number of steps, or time at
current walking speed).

Due to the limited number of phosphenes that can be generated by the current
technology, it may be better to present a symbolic representation.

For example, a small part of the grid (perhaps 5x5) could be used for information on
obstacle locations in the current environment. Auditory information could also be
provided in natural language. A scene description mode could be useful.
VISUAL PROSTHESIS CONSTRAINTS:

NUMBER OF PHOSPHENES:

Current technology limits the number of phosphenes that can be provided to the
patient. Additionally, the size, shape and brightness of phosphenes are not predictable,
although recent work in a 4x4 retinal prosthesis shows promise in overcoming these
problems.

REAL-TIME PROCESSING:

A visual prosthesis system needs to perform in real time. However, this has been
problematic for other image-based mobility systems, particularly those which are stereo-
vision based. One way of providing real-time processing may be to restrict the field of
view of the camera, although this would restrict the amount of preview (or time to
anticipate problems) available to a blind traveler.

ANOTHER DIMENSION:

Obviously, the first users of artificial retina technology will be blind people. It will be
a wonderful boon that will restore eyesight for millions of 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.
 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 reconfigure (by straining eye
muscles in some trained pattern) the retinas to look at different parts of the light spectrum
as well. Imagine, for instance, soldiers or police shifting their eyesight into the infrared
when on a dangerous night time operation. Or imagine just any person wanting to up his
light sensitivity when outside at night or in a room with little available light.

CONCLUSION:

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 robots and
smart sensors. The silicon retina can also be used in cameras for remote monitoring for
safety, identification and biometrics purposes.

Sufficiently advanced technologies developed to treat diseases will inevitably morph

into technologies that will enhance function. Research on artificial implants for blindness
is laying the groundwork for the eventual development of vastly superior, artificially
enhanced eyesight.