BIONIC EYE TECHNOLOGY
More than 250 years later, blindness is still one of the most debilitating sensory impairments, affecting close to 40 million people worldwide. Many of these patients can be efficiently treated with surgery or medication, but some pathologies cannot be corrected with existing treatments.
In particular, when light-receiving photoreceptor cells degenerate, as is the case in retinitis pigmentosa, or when the optic nerve is damaged as a result of glaucoma or head trauma, no surgery or medicine can restore the lost vision.
In such cases, a visual prosthesis may be the only option. Similar to cochlear implants, which stimulate auditory nerve fibers downstream of damaged sensory hair cells to restore hearing, visual prostheses aim to provide patients with visual information by stimulating neurons in the retina, in the optic nerve, or in the brain’s visual areas.
| Bionic eye |
WORKING OF THE NORMAL EYE:
In a healthy retina, photoreceptor cells—the rods and cones—convert light into electrical and chemical signals that propagate through the network of retinal neurons down to the ganglion cells, whose axons form the optic nerve and transmit the visual signal to the brain.
Prosthetic devices work at different levels downstream from the initial reception and biochemical conversion of incoming light photons by the pigments of photoreceptor rods and cones at the back of the retina.
Implants can stimulate the bipolar cells directly downstream of the photoreceptors, for example, or the ganglion cells that form the optic nerve. Alternatively, for pathologies such as glaucoma or head trauma that compromise the optic nerve’s ability to link the retina to the visual centers of the brain, prostheses have been designed to stimulate the visual system at the level of the brain itself.
DEFINITION OF BIONIC EYE:
- The bionic eye system will consist of a small digital camera, external processor and a implant with a microchip and stimulating electrodes surgically placed in the back of the eye.
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| BIONIC EYE CONSTRUCTION |
- A bionic eye mimics the function of the retina to restore sight for those with severe vision loss. It uses a retinal implant connected to a video camera to convert images into electrical impulses that activate remaining retinal cells which then carry the signal back to the brain.
MAIN PARTS OF BIONIC EYE:
- A digital camera that's built into a pair of glasses. It captures images in real time and sends images to a microchip.
- A video-processing microchip that's built into a handheld unit. It processes images into electrical pulses representing patterns of light and dark and sends the pulses to a radio transmitter in the glasses.
- A radio transmitter that wirelessly transmits pulses to a receiver implanted above the ear or under the eye
- A radio receiver that sends pulses to the retinal implant by a hair-thin implanted wire
- A retinal implant with an array of 60 electrodes on a chip measuring 1 mm by 1 mm
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| Parts of bionic eye |
WORKING OF BIONIC EYE:
The entire system runs on a battery pack that's housed with the video processing unit. When the camera captures an image -- of, say, a house -- the image is in the form of light and dark pixels. It sends this image to the video processor, which converts the tree-shaped pattern of pixels into a series of electrical pulses that represent "light" and "dark." The processor sends these pulses to a radio transmitter on the glasses, which then transmits the pulses in radio form to a receiver implanted underneath the subject's skin. The receiver is directly connected via a wire to the electrode array implanted at the back of the eye, and it sends the pulses down the wire.
When the pulses reach the retinal implant, they excite the electrode array. The array acts as the artificial equivalent of the retina's photoreceptors. The electrodes are stimulated in accordance with the encoded pattern of light and dark that represents the tree, as the retina's photoreceptors would be if they were working (except that the pattern wouldn't be digitally encoded). The electrical signals generated by the stimulated electrodes then travel as neural signals to the visual center of the brain by way of the normal pathways used by healthy eyes -- the optic nerves. In macular degeneration and retinitis pigmentosa, the optical neural pathways aren't damaged. The brain, in turn, interprets these signals as a house and tells the subject, "You're seeing a house"
It takes some training for subjects to actually see a house. At first, they see mostly light and dark spots. But after a while, they learn to interpret what the brain is showing them, and they eventually perceive that pattern of light and dark as a house.
COST AND VALUE OF BIONIC EYE:
The first version of the system had 16 electrodes on the implant and is still in clinical trials at the University of California in Los Angeles. Doctors implanted the retinal chip in six subjects, all of whom regained some degree of sight. They are now able to perceive shapes (such as the shaded outline of a tree) and detect movement to varying degrees. The newest version of the system should offer greater image resolution because it has far more electrodes. If the upcoming clinical trials, in which doctors will implant the second-generation device into 75 subjects, are successful, the retinal prosthesis could be commercially available by 2010. The estimated cost is $30,000.
IMPLANTED ELECTRODES TO BYPASS THE FAILED PARTS OF EYE:
As both cameras and our understanding of the visual system improve, new techniques to restore sight to the blind are progressing too. Devices like the Argus II are able to bypass damaged eyes to restore some vision to those who have lost it. It’s not the same as fully restored vision, and it’s still early days – there are only six people in the US with the Argus II – but researchers hope that as they learn more about vision they can help those who’ve lost it get it back.
But for those who have been blind for years, simply seeing shapes again is pretty exciting. “I’m very much looking forward to being able to see my grandchildren,” Fulton says. “I won’t be able to see their faces, but I know they’ll have great fun standing in a room and say ‘grandma find me!’ and I’ll be able to tell the difference between the four-year-old and the seven-year-old.”
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