There is no replacement for human sight. It is simply incomparable because of its capacity to see. Our life is full of pictures we daily see. Life without sight is dark. And blind people lead dark lives. As capable human beings, we need to do something more than just helping a blind person cross the road.
Belonging to the community of engineers – there is no frontier that we cannot conquer. If scientists give birth to ideas, then it is we engineers who put life into those ideas. Today, we have every tool in our hand. The ball is in our court! It is our turn now, to return what mankind has given us. What about bestowing sight for the blind? There is no magic wand to do this in a jiffy. But yes! We certainly know the magic route to reach our goal: Science and Technology.
Today, we talk of artificial intelligence that has created waves of interest in the field of robotics. When this has been possible, why not artificial vision? It is with this dream that I present this paper on Bionic Eyes. Sooner or later, this shall create a revolution in the field of medicine.
It is important to know few facts about the organ of sight i.e, the Eye before we proceed towards the technicalities involved.
How are we able to see?
Having seen the anatomical part of human eye, lets try to know as to how we are able to see – how is an image being formed?
For vision to occur, 2 conditions need to be met:
1.An image must be formed on the retina to stimulate its receptors (rods and cones).
2.Resulting nerve impulses must be conducted to the visual areas of the cerebral cortex for interpretation.
Four processes focus light rays, so that they form a clear image on the retina
1.refraction of light rays
2.accommodation of the lens
3.constriction of the pupil
4.convergence of the eyes
How is vision impaired?
Damage or degeneration of the optic nerve, the brain, or any part of the visual pathway between them, can impair vision. For example, the pressure associated with glaucoma can also damage the optic nerve. Diabetes, already cited as a cause of retina damage, can also cause degeneration of the optic nerve.
Damage to the visual pathway does not always result in total loss of sight. Depending on where the damage occurs, only a part of the visual field may be affected. For example, a certain form of neuritis (nerve inflammation), often associated with multiple sclerosis, can cause loss of only the center of the visual field – a condition called scotoma.
A stroke can cause vision impairment when the resulting tissue damage occurs in one of the regions of the brain that process visual information. For example, damage to an area that process information about colors may result in a rare condition called acquired cortical color blindness. This condition is characterized by difficulty in distinguishing any color – not just one or two colors as in the more common inherited forms of color blindness.
A more common treatment for curing blindness has been corneal transplantation. More about it:
Corneal Transplants:
Surgical removal of opaque or deteriorating corneas and replacement with donor transplants is a common medical practice. Corneal tissue is avascular; that is, the cornea is free of blood vessels. Therefore corneal tissue is seldom rejected by the body’s immune system. Antibodies carried in the blood have no way to reach the transplanted tissue, and therefore long-term success following implant surgery is excellent.
What are Bionic Eyes?
An artificial eye provokes visual sensations in the brain by directly stimulating different parts of the optic nerve.
There are also other experimental implants that can stimulate the ganglia cells on the retina or the visual cortex of the brain itself. There is more concentration given to the production of artificial retinas.
Here is the description of a Bionic Eye:
Many types of artificial eyes have been designed and research is still going on . There is no standard model in this case. Researchers are working out different types of concepts. Here are a few examples:
The prototype devices are 2 millimeters across and contain some 3,500 micro photodiodes. Placed behind the retina, this collection of miniature solar cells is designed to convert natural light to electrical signals, which are then transmitted to the brain by the remaining healthy parts of the retina.
A Belgian device has a coil that wraps around the optic nerve, with only four points of electrical contact. By shifting the phase and varying the strength of the signals, the coil can stimulate different parts of the optic nerve, rather like the way the electron guns in TVs are aimed at different parts of the screen. The video signals come from an external camera and are transmitted to the implant via a radio antenna and microchip beneath the skin just behind the ear.
Implants of a microchip, smaller than the head of a pin and about half the thickness of a sheet of paper were used to remove blindness.
Engineering details of the Bionic Eye:
First, for visually impaired people to derive the greatest benefit from an enhanced-vision system, the image must be adapted to their particular blind areas and areas of poor acuity or contrast sensitivity. Then the information arriving instantaneously at the eye must be shifted around those areas. The thrust of all prosthetic vision devices is to use an electrode array to give the user perceptions of points of light (phosphenes) that are correlated with the outside world. Thus, to achieve the expected shift of the image across the stimulating electrode array, the camera capturing the image must follow the wearer's eye or pupil movements by monitoring the front of the eye under infrared (IR) illumination. The eye-position monitor controls the image camera's orientation. If the main image-acquisition camera is not mounted on the head, compensation for head movement will be needed, as well.
Finally, if a retinal prosthesis is to receive power and signal input from outside the eye via an IR beam entering the pupil, the transmitter must be aligned with the intraocular chip. The beam has two roles: it sends power, and it is pulse- or amplitude-modulated to transmit image data. Under the control of eye movement, the main imaging camera for each eye can swivel in any direction. Each of these cameras--located just outside the users' field of view to avoid blocking whatever peripheral vision they might have--captures the image of the outside world and transmits the information through an optical fiber to a signal-processing computer worn on the body.
The surgery!
This concept of Artificial Vision is also interesting to engineers, because there are a number of technicalities involved in this surgery apart from the anatomical part.
The microsurgery starts with three incisions smaller than the diameter of a needle in the white part of the eye. Through the incisions, surgeons introduce a vacuuming device that removes the gel in the middle of the eye and replaces it with saline solution. Surgeons then make a pinpoint opening in the retina to inject fluid in order to lift a portion of the retina from the back of the eye, creating a pocket to accommodate the chip. The retina is resealed over the chip, and doctors inject air into the middle of the eye to force the retina back over the device and close the incisions.
During the entire surgery, a biomedical engineer takes part actively to ensure that there is no problem with the chip to be implanted.
Some facts about Bionic Eyes:
Scientists at the Space Vaccum Epitaxy Centre (SVEC) based at the University of Houston, Texas, are using a new material, comprising tiny ceramic photocells that could detect incoming light and repair malfunctioning human eyes. Scientists at SVEC are conducting preliminary tests on the biocompatibility of this ceramic detector.
The artificial retinas constructed at SVEC consist of 100,000 tiny ceramic detectors, each 1/20th the size of a human hair. The assemblage is so small that surgeons can’t safely handle it. So, the arrays are attached to a polymer film one millimeter in size. After insertion into an eyeball, the polymer film will simply dissolve leaving only the array behind after a couple of weeks.
The Analogy:
There is a great degree of coherence between the way our eyes function to that of a camera. Perhaps – our eyes had been the inspiration behind the camera’s invention. Here’s more about it:
From the structural point of view the eye may be compared with a camera. The eyelids act as a shutter and there is an entrance window for light – the cornea; a diaphragm to regulate the aperture and therefore the amount of light entering – the iris; a lens to focus the image; a darkened interior formed by the choroid, and a light –sensitive plate which receives the image – the retina.
Brain Implants:
There is one more concept similar to Bionic Eyes that is also making waves in the medical field and that is the use of Brain Implants to remove blindness.
In recent years, progress is being made towards sensory substitution devices for the blind. In the long run, there could be the possibility of brain implants. A brain implant or cortical implant provides visual input from a camera directly to the brain via electrodes in contact with the visual cortex at the backside of the head.
If we try to do a fair and objective comparison between auditory display technology and brain implant technology it should first be stressed that result of any comparisons can of course change over time as the respective technologies are further developed and refined.
The Challenges:
There are many very many obstacles to be overcome before Bionic Eyes become a success story.
Our eyes are perhaps the most sensitive of all organs in the human body. A nano-sized irritant
can create havoc in the eye.
- There are 120 million rods and 6 million cones in the retina of every
healthy human eye. Creating an artificial replacement for these is no
easy task.
- Si based photo detectors have been tried in earlier attempts. But Si
is toxic to the human body and reacts unfavorably with fluids in the eye.
- There are many doubts as to how the brain will react to foreign signals
generated by artificial light sensors.
- Infection and negative reaction are the always-feared factors. It is
imperative that all precautionary measures need to be ascertained.
Conclusion:
Restoration of sight for the blind is no more a dream today. Bionic Eyes have made this true.
Though there are a number of challenges to be faced before this technology reaches the
common man, the path has been laid. This paper has tried to present the concept of
Artificial Vision through a engineers viewpoint. Engineers play a major role in the design
stage of Bionic Eyes.
It is just a matter of 4-5 years, that the blind will be able to see through these Bionic Eyes;
thanks to Science and Technology.
References:
- Neural Implants – First Bionic Eyes by Victor Chase.
- Hitting the Nerve (from the New Scientist).
- Doctors Test Chips in Eyeballs to Restore Sight from azcentral.com
- www.dobelle.com
- Anthony’s textbook of Anatomy and Physiology - Gary A Thibodeau, Kevin T Patton
- Science Reporter (December 2004)
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