If a digital camera is used for analogy, the cornea and lens of the human eye are equivalent to the lens, the retina behind the eyeball is the photosensitive device, the optic nerve is equivalent to the line connecting the photosensitive device and the memory card, and the visual cortex at the back of the brain is Memory card and post-processing software. Diseases such as retinitis pigmentosa or age-related macular degeneration can cause the retina to lose function, making this camera unable to perceive any images; and the Second Sight company in the United States is trying to replace the malfunctioning retina with electronic devices. Help these patients regain their basic vision.
This technology is the artificial retina technology. It is similar to the principle of a cochlear implant-using current to stimulate a still intact nerve, so that the brain can receive signals and think that the senses are still working properly. Over the past 20 years, hundreds of thousands of people have received hearing through cochlear implants, but the progress of artificial retinas has been somewhat stagnant.
This is because the vision system is much more complicated. About 80% of the information we obtain comes from vision. People have not been able to make cameras comparable in performance to the human eye, and the precise correspondence between photoreceptor cells and optic nerve remains a mystery. Considering the technical limitations-the size of the artificial retinal chip is generally only a few square millimeters, and the thickness is less than 100 microns-it is quite difficult to obtain a vision as accurate as the human eye.
Although as early as 1924, it was discovered that the use of electrical stimulation on the visual cortex will produce phantom vision, but it was not until 1967 that an artificial visual device implanted in the visual cortex was developed. However, the visual quality produced by this method is very poor, and research in this field has gradually begun to shift from visual cortical implantation to retinal implantation. In the past 30 years, many research institutions and manufacturers have invested in this field, and the research ideas have been divided into two categories: subretinal implantation and extraretinal implantation technology.
Subretinal implantation technology is to implant the chip in the area between the retinal nerve sensory epithelium and the pigment epithelium, instead of the light-sensing cells to feel the light, and directly use the encoding and decoding mechanism of the retina itself to convert the electrical signal into vision. It still uses the patient's own "lens", just like changing a photosensitive device for a digital camera. This technology requires an external power supply unit, which is difficult to operate and has a small range of use, but does not require an external camera. The main researchers of the subretinal implant technology are the research team of the University of Chicago Alan Chow and the Eberhart Zrenner team of the University of Tubingen, Germany. The University of Tübingen has developed a prototype of this device, which has 1500 electrodes and is powered by a wireless power supply behind the ear, and the team has conducted 10 implant trials.
The extra-retinal implant technology is to attach the electrode array to the outer surface of the retina and directly stimulate nerve cells with signals from outside the eye, which is equivalent to completely replacing the lens and the photosensitive device. The main researchers in this field include the University of Bonn, Germany, Hopkins University, Massachusetts Institute of Technology and Harvard University, and the Doheny Institute of Ophthalmology at the University of Southern California. Second Vision ’s artificial retina technology was developed on the basis of the Dohany Institute.
In 1998, Dr. Robert Greenberg and Sam Williams founded the Second Vision Company. Sam himself was a patient with retinitis pigmentosa and lost confidence in public research in this field, so he decided to develop his own artificial retinal device that could be put into commercialization. Sam died in 2009 and did not have time to wait until the day when his goal was achieved. But his legacy will benefit many people.
Argus is the name of the Hundred Eyed Giant in Greek mythology. The artificial retina system named after it consists of a small camera, a microcomputer and some wireless communication tools. In 2002, inspired by an invention at the University of Southern California's Dohany Eye Institute, Argus I was developed with 16 electrodes. Between 2002 and 2004, a total of 6 experimental implants were performed. These patients have a simple sense of light, can judge the movement of objects, and can distinguish objects from the background.
For this type of technology, the more electrodes you have, the more points you can see. The Argus II now has 60 electrodes. Since 2006, it has allowed 40 patients to regain basic vision, and some of them have been able to distinguish objects, shapes, and even read large prints. Although users need a certain level of training to understand what the light point in the field of vision means, it is better than fumbling in the dark world.
Argus II is not a treatment for blindness, but only a treatment for certain retinal diseases. According to the statistics of the World Health Organization, there are more than 45 million people with visual impairment in the world, and an average of 1 person deteriorates every 5 seconds. It is estimated that by 2020, the visually impaired population will increase to 76 million; Development, the number of patients with age-related macular degeneration will also increase. All Argus II can do is to help these patients achieve a better quality of life.
The artificial retinas will be first tested in hospitals in London, Manchester, Paris and Geneva, and will be sold in the United States once approved by the US Food and Drug Administration. Second Vision hopes to sell 100 implanted devices in the first year, each with a price tag of US $ 100,000. "Although this price seems a bit high," Dr. Greenberg said, "but this is actually the same as the price of the first cochlear implant." He hopes that Argus II will be included in the government's subsidy program so that the price will become easier accept.
Currently, the company has applied for 76 patents in the United States. Now they have prepared animal experiments for Argus III. The new generation of artificial retinas will have hundreds of electrodes.
Although the current Argus can only let people see some light spots, its future will be unlimited. The technology just launched to the market will not be the final version, these light spots have already shown hope.
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