- 2777 - EYE - a prosthetic eye for artificial vision? - In 2005 a medical team invented a prosthetic eye, artificial vision, for the blind. Many people are blind due to a medical condition where the eye has deteriorated photo sensors in the back of the retina. In 2020 bionic eye technology is in its infancy but it will do more than prosthetic eyes. Bionic eye implants work inside the existing eye structures or in the brain. They are designed to achieve functional vision.
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-------------------------- 2777 - EYE - a prosthetic eye for artificial vision?
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- This Review covers the development of artificial vision for the blind that will someday be artificial eyesight for robots. From 2005 to 2020 we are fast approaching the vision where robots have vision much like humans. What next?
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- In 2005 a prosthetic eye, artificial vision, was deigned tp bring vision to the blind. In 2005, 30 million people were blind with a medical condition where the eye has deteriorated photo sensors in the back of the retina. The cones and rods are dead, even though the neuron cells are working fine and can send signals to the brain, the photo detectors are gone, so no signal gets started. There is no cure for this disease.
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- In 2005 we have an ear implant that provides hearing for the deaf. There have been over 50,000 implants by 2005. A wire of electrodes is inserted into the ear’s spiral cochlear canal. The wire and a wireless radio are implanted under the skin behind the ear.
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- A radio receiver is mounted on the outside of the skin behind the ear. The microphone picks up the sounds, amplifies them and sends them into the electrodes implanted in the ear. The person’s brain learns how to make sense out of what she hears. Its amazing.
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- The Stanford medical team thinks they can do the same thing for the blind with their prosthetic eye. There are 1,100,000 blind people in the United States.
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- Stanford has installed the device in rats and pigs. The process implants electrodes on the retina at the back of the eye. It uses the neurons in the eye and the optic nerve to send signals to the brain.
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- A German team, the Dobelle Group, had a different approach. They implant the electrodes directly on the back of the brain, the visual cortex. They implant inside the skull.
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- Another approach is being tried where there is a bed of nails approach. They pound these spikes of electrodes through the back of the skull. But in 2005, 19 people already had his operation. One person had been seeing with it for 12 years.
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- One of their patients was driving a car with this device. The patient has a camera mounted in on eye goggles. He has a fanny pack of computer and power supply. He has a cable going to the back of his head that connects to 64 electrodes on a 3 x 3 centimeter plate implanted on the surface of his brain’s cortex. And, he can see. It’s amazing.
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- What does he actually see? The image processing detects edges, so he can see the frame of a door. But cannot see smooth images. He had to feel for the door handle on the car, for example. He sees all shades of gray, no color. He judges distance by the relative size of things since there is not parallax. Yet, the brain can figure these senses out and the blind person can see.
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- A healthy retina is 150 microns, or 150 micro meters, or 150*10^-6 meters, .0000015 centimeters thick. It’s rods and cones photo detectors are equivalent to a 100 mega pixel digital camera. The rods detect light gray to dark gray, the cones detect red, green, and blue light. The retina has 6% cones and 94% rods. The 100,000,000 pixels image down to 1,000,000 axons that transmit the signals through the optic nerve to the visual cortex of the brain.
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- The electrodes are photo-diodes that are implanted by the eye surgeon on the back of the eye. The electrodes can not have much voltage or current or they will damage the eye. So the electrodes must be very close to the neuron cells.
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- To accomplish this the electrodes are mounted on pillars and chambers that are 10 microns diameter and 70 microns tall, remember the retina wall is 150 microns thick. The cells migrate around the pillars and into the chambers just like a wound would heal. This puts the electrodes at the proper depth in the retina wall to stimulate the proper cells.
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- The damage threshold for the electrodes is 150 millivolts. The stimulation threshold is 15 millivolts. 150 to 15 mv will give a dynamic range of 10 to 1, or 10 different shades of gray to the vision. A 1 millisecond voltage pulse is used so as to not heat up the eye. Every 7 milliwatts of electric energy will raise the temperature of the eve 1 degree centigrade.
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- The electrode array of 18,000 pixels will give a 10 degree window of 20/80 vision acuity. 20/400 is legal blindness for driving in California. 20/20 is perfect vision. The array has 2,500 pixels per square millimeter. Each pixel is 20 microns diameter. Each electrode is 10 microns in diameter.
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- Once the photo detection is complete by this artificial means there is still a lot of image processing to be done. The eye is constantly moving so it is scanning across different photo sensors all the time.
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- The visual goggles used have infrared scanners that cause movement across the photodiodes to simulate the eye movement. A photovoltaic power supply is mounted around the lens of the eye because the photodiodes need 1000 times more power to work than do the eyes healthy photo sensors.
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- A bright day produces 1 microwatt per square millimeter on the eye. The photo diodes need 1,000 microwatt to operate. Remember 7,000 microwatts will raise the temperature of the eye 1 degree Centigrade. So, the power to the photodiodes is kept at 1/10 that amount of power.
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- The image processing is a long chain of interpretations starting at the retina, the neuron axons, the optic nerve and finally the brain itself. A great deal of this product is the software that simulates the brains interpretation as naturally as possible.
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- Stanford hopes to have human patients with this prosthetic eye in 2006.
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- In 2020 there were nearly 40 million people suffering from blindness worldwide and another 124 million affected by low vision.
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- Bionic eye scientists have one common goal to develop technology that's as effective for visual disabilities as cochlear implants have become for auditory ones. In 2020 bionic eye technology is still in its infancy compared with cochlear implants for hearing loss.
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- Several bionic eye implants are in development with one is available in the United States that is suitable only for blindness caused by specific eye diseases.
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- Bionic eyes do more than prosthetic eyes. Bionic eye implants work inside the existing eye structures or in the brain. They are designed to achieve functional vision goals.
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- The Argus II Retinal Prosthesis System consists of a tiny eyeglasses-mounted camera and a transmitter that wirelessly sends signals to an electrode array that is implanted onto the damaged retina of a blind person.
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- Just as there is no single cause for blindness, there's likewise no one cure. To determine whether a bionic eye could help you see, it's important to know the reason for your vision loss.
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- The process of sight begins when light enters the eye. The cornea and lens focus light onto the retina at the back of the eyeball. Light-sensitive cells in the retina then convert the focused light into electrical energy, which is transported to the brain via the optic nerve.
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- In blind people, part of this process doesn't work. In some cases, the cornea or lens are damaged or diseased, or the retina can't perceive light. In others, the signal is lost somewhere along the visual pathway in the brain.
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- Different bionic eye models take aim at different target areas in the visual pathway. Currently, retinal implants are the only approved and commercially available bionic eyes, though cornea transplants and cataract surgery can replace the cornea and lens if these structures are clouded or are incapable of focusing light for other reasons.
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- The FDA has approved just one commercially available bionic eye system. The device, called the Argus II Retinal Prosthesis System, was developed by a California-based company called Second Sight.
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- The Argus II has been used to restore some level of visual perception to hundreds of individuals with severe retinitis pigmentosa, a disease that affects one in 5,000 people. The Argus II also is being tested for people with a much more common condition, age-related macular degeneration.
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- It is a two-part system that includes a small camera that is mounted on a pair of eyeglasses and a tiny array of electrodes that is implanted in the back of the eye, on the retina.
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- Whatever the camera sees is converted into signals that are transmitted wirelessly to the retinal implant. In response, the chip's electrodes stimulate the retinal cells, causing them to send the incoming information to the optic nerve so it can be processed by the brain.
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- Although this system enables people to discern light, movement and shapes, it does not yet restore sight to the extent some might hope. This limitation is largely due to the fact that the current implant has only 60 electrodes. To see naturally, you'd need about a million electrodes.
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- However, users can function well enough to read large-print books and cross the street on their own. And the company plans to add more electrodes in future models.
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- Another limitation is that it doesn't enable users to perceive colors. Future iterations will likely feature advanced implants with higher numbers of electrodes that are capable of producing sharper, more functional vision for people who are blind from retinitis pigmentosa and other retinal diseases, including macular degeneration. It's possible future implants may also be able to produce some degree of color vision.
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- Researchers in 2020 are testing devices with even more electrodes, as well as devices that bypass the retina and stimulate the brain directly. Teaching the blind to see. Robots will soon be next to be able to operate on their own with vision feedback just like us. Let’s hope they don’t learn to overpower us.
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- July 20, 2020 566 2777
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--------------------- Tuesday, July 21, 2020 -------------------------
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