Thursday, July 24, 2008
Retinal Prosthesis
There are two major categories of retinal prosthesis’ known as subretinal and epiretinal prosthesis, and they differ in the location of their light receptors. As their names imply, subretinal means the artificial photoreceptors are located underneath the retina, and epiretinal means they are on top of the retina. Based on these characteristics alone, the subretinal would seem to be the wisest choice for a patient wanting to restore their vision; having eyes outside of your head is unnatural and makes them more prone to damage. Neither can you move them like you can your eyes. However, there are differences in their safety and ultimate effectiveness that go beyond the simple location of the light receptors.
Namely, these differences have to do with the way in which the device is connected to the brain. The major ways in which you can connect prosthesis with the brain are: 1 Implanting a MEMS (Micro Electrical Mechanical System) in the retina 2 Implanting a MEMS in the optic nerve 3 Implanting a MEMS into the skull 4 Implanting a hybrid retinal device. Out of all these methods, the most sophisticated and promising seems to be the hybrid retinal device for the following reasons.
Normal retinal and optic nerve implants cannot work if ganglion cells and the optic nerve are damaged, and would not be able to assist a majority of patients who suffer blindness. However, the solution for this problem, placing a MEMS in the skull, is a complex and dangerous procedure due mainly for increased chance of cell proliferation, whereas retinal and optic nerve implants can be installed/fixed with common and relatively safe procedures. Though there are others problems with all these implants, including power supply, difficulty in signal transmission, blurred images, and wear of artificial material, a hybrid retinal device succeeds where the other three do not; it is a relatively safe procedure and it does not require the optic nerve and/or retina to be intact. Like a cortical implant, it is epiretinal (a small put down, but in comparison to its advantages, insignificant), but unlike a cortical implant it uses neural grafts to build a connection through the damaged retina. The surgery required to implant it would be similar to retinal and optic nerve MEMS’, making it safer, and, when compared to other methods of connecting visual prosthesis, the obvious choice for the job.
Namely, these differences have to do with the way in which the device is connected to the brain. The major ways in which you can connect prosthesis with the brain are: 1 Implanting a MEMS (Micro Electrical Mechanical System) in the retina 2 Implanting a MEMS in the optic nerve 3 Implanting a MEMS into the skull 4 Implanting a hybrid retinal device. Out of all these methods, the most sophisticated and promising seems to be the hybrid retinal device for the following reasons.
Normal retinal and optic nerve implants cannot work if ganglion cells and the optic nerve are damaged, and would not be able to assist a majority of patients who suffer blindness. However, the solution for this problem, placing a MEMS in the skull, is a complex and dangerous procedure due mainly for increased chance of cell proliferation, whereas retinal and optic nerve implants can be installed/fixed with common and relatively safe procedures. Though there are others problems with all these implants, including power supply, difficulty in signal transmission, blurred images, and wear of artificial material, a hybrid retinal device succeeds where the other three do not; it is a relatively safe procedure and it does not require the optic nerve and/or retina to be intact. Like a cortical implant, it is epiretinal (a small put down, but in comparison to its advantages, insignificant), but unlike a cortical implant it uses neural grafts to build a connection through the damaged retina. The surgery required to implant it would be similar to retinal and optic nerve MEMS’, making it safer, and, when compared to other methods of connecting visual prosthesis, the obvious choice for the job.
Epiretinal and Subretinal implants
I believe that the epiretinal implant will work the best in patients. It does not require any intact optics, which would prove more useful in patients who have little to no vision at all. The ganglia are directly stimulated with an epiretinal implant, while the subretinal implant uses the remaining neurons of the old retinal network. The epiretinal implant is much harder to fix in place, but it provides better “connections” to the brain. It is simply a readout chip that receives signals from an external camera, which is simpler than the subretinal device which actually contains light sensors. Both devices have shown the ability to be biocompatible with cats, proving that one day they might be suitable for human use.
Sources
"Retinal implant." Wikipedia, The Free Encyclopedia. 25 Feb 2008, 21:29 UTC. Wikimedia Foundation, Inc. 24 Jul 2008.
Will Retinal Implants Restore Vision?
Eberhart Zrenner (8 February 2002)
Science 295 (5557), 1022. [DOI: 10.1126/science.1067996]
Sources
"Retinal implant." Wikipedia, The Free Encyclopedia. 25 Feb 2008, 21:29 UTC. Wikimedia Foundation, Inc. 24 Jul 2008
Will Retinal Implants Restore Vision?
Eberhart Zrenner (8 February 2002)
Science 295 (5557), 1022. [DOI: 10.1126/science.1067996]
Epiretinal Implant
I think that epiretinal implants will work the best in the future. Epiretinal prosthesis chronically implanted in blind patients allows them to perceive discrete phosphenes and perform visual spatial tasks. According to a presentation at the Cannes Retina Festival 24th Annual Meeting of the American Society of Retina Specialists (ASRS) & 6th Annual Meeting of the European Vitreoretinal Society (EVRS), held in Cannes, France, five patients implanted with the device (Second Sight Medical Products, Sylmar, Calif) continue to use it daily. “These patients are using the prosthesis to perform tasks such as finding doorways, following the action in sporting events, navigating, following individuals, locating objects across the room and eating,” said Robert J. Greenberg, MD, PhD, president and CEO of Second Sight..
Epiretinal Prosthesis Shows Promise for Blind Patients
BY CONNI BERGMANN KOURY, EDITOR-IN-CHIEF
Epiretinal Prosthesis Shows Promise for Blind Patients
BY CONNI BERGMANN KOURY, EDITOR-IN-CHIEF
Subretinal Implants
After examining the various types of retinal implants, the subretinal implant appears to be the best choice. Unlike the epiretinal and hybrid implants, the subretinal does not have any external devices. The majority of patients tend to feel more comfortable about having operations if they will appear the same afterwards; it feels more normal for patients to have only internal devices. The subretinal implant appears more normal and functions closer to how a healthy retina actually functions.
In a subretinal implant light is taken from the environment directly, similar to how a healthy retina does. The light received is then converted into electrical signals which stimulate the cell layers that are still capable. Unlike the subretinal, the epiretinal implant uses a sensor to encode information as electrical impulses; thus making the epiretinal implant more complex than is necessary. Not only is the epiretinal implant more complex in its information processing, but it is much more difficult to fix. Although the hybrid retinal implant appears to be an idea that could function well as it combines some of the better aspects of other retinal implants, there is not sufficient experimental data for me to support the implant. The implant that is most similar to an actual retina is the subretinal implant; therefore it is more likely to have better results because it uses the biological functions available.
References:
http://www.opticsreport.com/content/article.php?article_id=1007
http://www.sciencemag.org/cgi/content/full/295/5557/1022
http://ieeexplore.ieee.org/iel5/6569/17543/00812432.pdf?arnumber=812432
In a subretinal implant light is taken from the environment directly, similar to how a healthy retina does. The light received is then converted into electrical signals which stimulate the cell layers that are still capable. Unlike the subretinal, the epiretinal implant uses a sensor to encode information as electrical impulses; thus making the epiretinal implant more complex than is necessary. Not only is the epiretinal implant more complex in its information processing, but it is much more difficult to fix. Although the hybrid retinal implant appears to be an idea that could function well as it combines some of the better aspects of other retinal implants, there is not sufficient experimental data for me to support the implant. The implant that is most similar to an actual retina is the subretinal implant; therefore it is more likely to have better results because it uses the biological functions available.
References:
http://www.opticsreport.com/content/article.php?article_id=1007
http://www.sciencemag.org/cgi/content/full/295/5557/1022
http://ieeexplore.ieee.org/iel5/6569/17543/00812432.pdf?arnumber=812432
Subretinal Implants
Subretinal implants is a device which is implanted between the pigment epithelial layer and the outer layer of the retina. Many microelectrodes are placed onto a very thin plate which is then inserted under the retina. Light which falls on the retina activates a current resulting in a stimulation of sensory neurons from the retina. The information is sent directly then to the optic nerve exactly like a normal eye. This subretinal implant directly mimics the natural function of the retina, thus making this procedure better than the epiretinal implant. With the subretinal implant, the eye can function normally without any wires hanging around.
Subretinal implants have a promising future because they can fix the problem with the most efficency and ease.
http://www.opticsreport.com/content/article.php?article_id=1007
Subretinal implants have a promising future because they can fix the problem with the most efficency and ease.
http://www.opticsreport.com/content/article.php?article_id=1007
Subretinal Implants
Eric Shine
Engineering Biomedical Systems
July 24, 2008
Subretinal Implants
The subretinal implant strategy will likely work the best in the future. Subretinal devices contain hundreds to thousands of light sensitive microphotodiodes that get stimulated by light. The stimulation passes from the photodiodes to microelectrodes that send the electrical signal to the optic nerve; from the there the signal goes to the visual cortex of the brain. Subretinal prostheses have a number of advantages over epiretinal devices. One is that the microphotodiodes placed directly over the damaged photoreceptor cells. Also since these devices do not rely on wireless interfacing with an external camera the signals between the devices the chances of a disturbance is less likely to happen. Another advantage with subretinal prosthesis is because the person with the device can still focus on objects with there eyes.Also there are aesthetic advantages has well, people do not have to where glasses with camera which could be unpleasing, as well, people who have epiretinal implants have to maintain, and keep up with the camera / glasses. One major downside to having either subretinal / epiretinal impants, the networking between the retina and the brain via the optic nerve must not be damaged.
Currently subretinal devices under testing that use the light received through the eye as a power source, like a solar panel; even though it is not the most powerful devices on the market, compared to an epiretinal and subretinal devices that have an external powersource, this type of device shows the most promise. This type of subretinal device would only have to consist of one chip that would contain a power source, mircoelectrodes and microphotodiodes. Since this type of device would only require one chip methods for implanting this device could be improved to make surgery less complicated and less time consuming. I believe this type of retinal device is the better of the two because it is less noticeable, it has a simple design, and the imaging capability is comparable to an epiretinal device.
References:
www.sciencemag.org/cgi/content/full/295/5557/1022
ieeexplore.ieee.org/iel5/2220/35447/01683653.pdf
Engineering Biomedical Systems
July 24, 2008
Subretinal Implants
The subretinal implant strategy will likely work the best in the future. Subretinal devices contain hundreds to thousands of light sensitive microphotodiodes that get stimulated by light. The stimulation passes from the photodiodes to microelectrodes that send the electrical signal to the optic nerve; from the there the signal goes to the visual cortex of the brain. Subretinal prostheses have a number of advantages over epiretinal devices. One is that the microphotodiodes placed directly over the damaged photoreceptor cells. Also since these devices do not rely on wireless interfacing with an external camera the signals between the devices the chances of a disturbance is less likely to happen. Another advantage with subretinal prosthesis is because the person with the device can still focus on objects with there eyes.Also there are aesthetic advantages has well, people do not have to where glasses with camera which could be unpleasing, as well, people who have epiretinal implants have to maintain, and keep up with the camera / glasses. One major downside to having either subretinal / epiretinal impants, the networking between the retina and the brain via the optic nerve must not be damaged.
Currently subretinal devices under testing that use the light received through the eye as a power source, like a solar panel; even though it is not the most powerful devices on the market, compared to an epiretinal and subretinal devices that have an external powersource, this type of device shows the most promise. This type of subretinal device would only have to consist of one chip that would contain a power source, mircoelectrodes and microphotodiodes. Since this type of device would only require one chip methods for implanting this device could be improved to make surgery less complicated and less time consuming. I believe this type of retinal device is the better of the two because it is less noticeable, it has a simple design, and the imaging capability is comparable to an epiretinal device.
References:
www.sciencemag.org/cgi/content/full/295/5557/1022
ieeexplore.ieee.org/iel5/2220/35447/01683653.pdf
The Best kinds of Retinal Implants
The most prevalent forms of retinal implants in this day of increasing research in the area are the epiretinal and subretinal implants. In reality, neither is perfect, and both have their positives and negatives, just as you would expect from a growing field of research. But in my opinion, the aspects of one clearly outweigh the other. I believe that overall positive aspects of the epiretinal implant make it the retinal implant of choice in these situations of medical blindness.
The epiretinal implant is one that is placed in the inner retinal membrane. It requires no photoreceptors and relies upon an external camera of sorts to send it information that it can later relay to the ganglions in the eye by way of electrodes. The obvious limitations to this lie in its reliance on external sources of infomation, rather than the neurons of the optic nerve itself, as does the subretinal implant, which is placed between the pigment epithelial layer and the outer layer of the retina. But I also believe that therein lies the appeal to the epiretinal implant. The fact that it wouldn't need to rely on possibly diseased or dying cells makes it at least seem more efficient.
Among the detractors to the epiretinal implants is the fact that because they rely on an external source, the device itself must do the extraordinarily difficult task of interpreting the visual information into electrical signals and commands. Despite this enormous task, the epiretinal seems to me to be the better option considering that it mustn't rely on damaged cells. The use of external cameras and their images (if interpreted properly) also "optimizes the signal received by the implants" (Optics Report).
Of course, assumptions should be made lightly concerning these implants, especially during their experimental phases. The best information and determination will come later from human testing (when approved), seeing as the implants have seen most of their testing in blind and healthy rats, cats, and dogs.\
The epiretinal implant is one that is placed in the inner retinal membrane. It requires no photoreceptors and relies upon an external camera of sorts to send it information that it can later relay to the ganglions in the eye by way of electrodes. The obvious limitations to this lie in its reliance on external sources of infomation, rather than the neurons of the optic nerve itself, as does the subretinal implant, which is placed between the pigment epithelial layer and the outer layer of the retina. But I also believe that therein lies the appeal to the epiretinal implant. The fact that it wouldn't need to rely on possibly diseased or dying cells makes it at least seem more efficient.
Among the detractors to the epiretinal implants is the fact that because they rely on an external source, the device itself must do the extraordinarily difficult task of interpreting the visual information into electrical signals and commands. Despite this enormous task, the epiretinal seems to me to be the better option considering that it mustn't rely on damaged cells. The use of external cameras and their images (if interpreted properly) also "optimizes the signal received by the implants" (Optics Report).
Of course, assumptions should be made lightly concerning these implants, especially during their experimental phases. The best information and determination will come later from human testing (when approved), seeing as the implants have seen most of their testing in blind and healthy rats, cats, and dogs.\
- "Will retinal implants restore vision?". Zrenner, Eberhart. Science 2002.
. - "Optoelectronic implants to treat visual diseases." Optics report. June 14, 2003.
Subretinal VS Epiretinal
Subretinal
-All replacements are made within the eye, no external device needed
-Replaces the rods and cones with silicon plate containing light sensitive microphotodiodes attached to an electrode
-light stimulates the microphotodiodes which then sends a message from the electrode to the remaining neural cells
Epiretinal
-Uses an external camera to receive electrical signals
-Electrodes from the implant then stimulate directly stimulate the axons that form on the optic nerve
I think that Epiretinal Implants would work the best, but Subretinal Implants are ideal. I believe Epiretinal implants would work better simply for the reason that less can go wrong and it is easier to repair if something does in fact go wrong. If a subretinal implant malfunctions, to repair it a doctor must go into the eye every time, unlike if a Epiretinal Implant malfunctions. However, for the patient, Subretinal Implants would be the best option, simply on account of appearance and convenience. Personally, I would not wan't to walk around with a camera on my head and wires running from the camera to my eye. So, at the moment, I feel that Epiretinal implant are more plausible, but in the future Subretinal Implants will be most desired.
-All replacements are made within the eye, no external device needed
-Replaces the rods and cones with silicon plate containing light sensitive microphotodiodes attached to an electrode
-light stimulates the microphotodiodes which then sends a message from the electrode to the remaining neural cells
Epiretinal
-Uses an external camera to receive electrical signals
-Electrodes from the implant then stimulate directly stimulate the axons that form on the optic nerve
I think that Epiretinal Implants would work the best, but Subretinal Implants are ideal. I believe Epiretinal implants would work better simply for the reason that less can go wrong and it is easier to repair if something does in fact go wrong. If a subretinal implant malfunctions, to repair it a doctor must go into the eye every time, unlike if a Epiretinal Implant malfunctions. However, for the patient, Subretinal Implants would be the best option, simply on account of appearance and convenience. Personally, I would not wan't to walk around with a camera on my head and wires running from the camera to my eye. So, at the moment, I feel that Epiretinal implant are more plausible, but in the future Subretinal Implants will be most desired.
Retinal Implants
Retinal Implants
Over the course of time the subretinal devices will surpass the effectiveness of epiretnal and cortical ones. A rule of biomedical engineering is to try and make the device as simple as possible. This way less things can possibly go wrong because the more things you try to mimic the more room there is for error. The cortical implants replace more organs than the subretinal and epiretnal ones. The optic nerve is used to convert collected light into electrical signals. In cortical devices the programmers have to do this on their own. There is a much better chance that the already present optic nerve would create a better mental image than a programmer trying to understand the body’s encoding system. Also in epiretnal devices a similar process goes on in which a “smart” computer chip has to convert stimuli from an external camera into electrical impulses that the brain can understand. Another problem with the other two devices is that they are not utilizing something very complicated and effective that is already there, the other part of the retina that is not damaged. Using the actual retina instead of an external camera would help the patient have a better sense of real eyesight. With cameras on glasses the patient would only get a forward view and would not get the advantages of peripheral vision. Subretinal devices would allow the person to “look around” by actually moving their eyes without having to move their head. It is this advantage of utilizing the already present organs and reducing the complexity of the device that will make the subretinal devices superior to the others.
Over the course of time the subretinal devices will surpass the effectiveness of epiretnal and cortical ones. A rule of biomedical engineering is to try and make the device as simple as possible. This way less things can possibly go wrong because the more things you try to mimic the more room there is for error. The cortical implants replace more organs than the subretinal and epiretnal ones. The optic nerve is used to convert collected light into electrical signals. In cortical devices the programmers have to do this on their own. There is a much better chance that the already present optic nerve would create a better mental image than a programmer trying to understand the body’s encoding system. Also in epiretnal devices a similar process goes on in which a “smart” computer chip has to convert stimuli from an external camera into electrical impulses that the brain can understand. Another problem with the other two devices is that they are not utilizing something very complicated and effective that is already there, the other part of the retina that is not damaged. Using the actual retina instead of an external camera would help the patient have a better sense of real eyesight. With cameras on glasses the patient would only get a forward view and would not get the advantages of peripheral vision. Subretinal devices would allow the person to “look around” by actually moving their eyes without having to move their head. It is this advantage of utilizing the already present organs and reducing the complexity of the device that will make the subretinal devices superior to the others.
Retinal Impants
Retinal implants are a new technological advance that is used to help patients see that lost their sight due to degenerative eye conditions. People with degenerative eye conditions loose there site due to the retinal cells losing their ability to sense light. The retinal implants help take over for the job of sensing the light. The next generation of retinal implants that has just received approval from the FDA, is a tiny chip with tiny hair-like electrodes. When the chip is implanted in the retina, it sends messages to the neural cells in the brain that send the information to the brain.
The result of the new generation of retinal implants seems very promising. The new generation of retinal implants almost quadrupled the number of electrodes from 16 to 60. Having a device with 60 electrodes is does not give the patient very clear vision better than having nothing. I believe the retinal implants have a very promising future. It may take many years to have an advancement that would let people see very clearly, but I think with the retinal implants it can be possible.
http://www.technologyreview.com/Biotech/18193/page2/
http://en.wikipedia.org/wiki/Retinal_implant
Subretinal Implants
Subretinal Implants
Dennis Xuan
Subretinal Implants are placed behind the retina and act as closely as possible to normal, healthy retinas. The subretinal implants mimic a normal retina’s ability to take in light and converts the information into electrical signals that are sent to the rest of the eye for processing. After that the information is sent down the optic nerve and acts in exactly the same way as a normal eye from then on.
The subretinal approach is also more preferable than Epiretinal since it has more direct approach to the problem physically. Instead of stimulating the nerve cells dealing with vision the subretinal approach just mimics the function of a damaged retina. Structurally it is also preferable since it is fully implanted and there are no dangly wires around.
So since the Subretinal approach is the most simple structurally and fixes the problem in the simplest way I believe that it will probably be the most promising eye implant for the future.
Optic Nerve Implant
The optic nerve implant is an entirely different and new approach from the subretinal or epiretinal implants. Instead of working with the retina, a spiral cuff nerve electrode is implanted and attached to the optic nerve. This cuff is implanted intercranially with a cable passing through the skull and skin to the outer surface. Then it also passes through the neck and comes out below the clavicle. Fortunately there are no acute or chronic symptoms for this electrode. The implantation of the cuff has been proven to be a very safe and reliable medical procedure. The equipment used is biocompatible and efficient for electrical stimulation.
The cuff works by stimulating the nerve fibers electronically. This produces phosphene sensitivity over a large portion of the visual field. This image is then captured by a camera and then transferred to the electrode array which stimulates the optic nerve. Over a certain period of time, patients with optic nerve implants will be able to recognize patterns in color, motion, and spatial localization.
Optic nerve implant research has been positively received since it does not require large processing equipment or power such as the other implants. I believe that as the future approaches, more and more research will follow the optic nerve since it seems to be more cost efficient and the equipment has been proven to be safe and reliable.
http://www.escrs.org/eurotimes/September2003/3.asp
http://www.pages.drexel.edu/~dh329/bmes212/opticnerve.html
(I realize my memo was supposed to be on retinal implants but I thought it would be interesting to see the other forms of implants)
The cuff works by stimulating the nerve fibers electronically. This produces phosphene sensitivity over a large portion of the visual field. This image is then captured by a camera and then transferred to the electrode array which stimulates the optic nerve. Over a certain period of time, patients with optic nerve implants will be able to recognize patterns in color, motion, and spatial localization.
Optic nerve implant research has been positively received since it does not require large processing equipment or power such as the other implants. I believe that as the future approaches, more and more research will follow the optic nerve since it seems to be more cost efficient and the equipment has been proven to be safe and reliable.
http://www.escrs.org/eurotimes/September2003/3.asp
http://www.pages.drexel.edu/~dh329/bmes212/opticnerve.html
(I realize my memo was supposed to be on retinal implants but I thought it would be interesting to see the other forms of implants)
What retinal implant should you be eyeing?
In the realm of retinal implants, there exists three types, epiretinal, subretinal, and cortical. All three show promise to restoring vision in some manner, though each have their associated benefits and risks.
Epiretinal implants, are applied to the outermost layer of the retina, this receieves signals from a peripheral camera and then transmits these electrical impulses of the image to the intact retina and optic nerve. The benefits of an epiretinal implant is that the camera could and conversion process could be tuned and more honed while implanted, and makes replacement/upgrading of the camera an easier process should it be neccessary. Negatives about this system are obviously the fact that it's asthetics aren't the most pleasing, epiretinal implants also can't be used on damaged retinas. The next form of implants, subretinal implants, is put on the photoreceptor level of the retina. This chip does all the ligth detection and conversion work there, without a camera. This system is good because it can be used in persons who have suffered from retinal degeneration. The negatives to this procedure is that it's slightly more invasive, and that the image could be worse than that of epiretinal. The final form of retinal implants involves a cortical implant. This implant is used in patients who have deteriorated optical nerves. This method involves direct interaction with the brain via the visual cortex. The visual cortex is hooked up to a camera setup which converts the images into electrical impulses that travel to the brain. The problem with this system is: cost, dangers of direct brain implantation ie. menengitis and scar tissue formation, not that great of a resolution, and asthetic problems. The good about it is that it works for patients who have optical nerve degeneration.
The best of these systems is subretinal implants, this is because they are less noticeable, require less maitenence, is pretty safe, and does pretty much just as well image wise as epiretinal implants.
http://www.seeingwithsound.com/etumble.htm
http://www.opticsreport.com/content/article.php?article_id=1007
Epiretinal implants, are applied to the outermost layer of the retina, this receieves signals from a peripheral camera and then transmits these electrical impulses of the image to the intact retina and optic nerve. The benefits of an epiretinal implant is that the camera could and conversion process could be tuned and more honed while implanted, and makes replacement/upgrading of the camera an easier process should it be neccessary. Negatives about this system are obviously the fact that it's asthetics aren't the most pleasing, epiretinal implants also can't be used on damaged retinas. The next form of implants, subretinal implants, is put on the photoreceptor level of the retina. This chip does all the ligth detection and conversion work there, without a camera. This system is good because it can be used in persons who have suffered from retinal degeneration. The negatives to this procedure is that it's slightly more invasive, and that the image could be worse than that of epiretinal. The final form of retinal implants involves a cortical implant. This implant is used in patients who have deteriorated optical nerves. This method involves direct interaction with the brain via the visual cortex. The visual cortex is hooked up to a camera setup which converts the images into electrical impulses that travel to the brain. The problem with this system is: cost, dangers of direct brain implantation ie. menengitis and scar tissue formation, not that great of a resolution, and asthetic problems. The good about it is that it works for patients who have optical nerve degeneration.
The best of these systems is subretinal implants, this is because they are less noticeable, require less maitenence, is pretty safe, and does pretty much just as well image wise as epiretinal implants.
http://www.seeingwithsound.com/etumble.htm
http://www.opticsreport.com/content/article.php?article_id=1007
Visual Prosthetics: Cortical and Sub-retinal
Ultimately, I believe that Cortical will eventually be the most effective type of vision-replacement. Once the technology goes wireless, the images from the camera source will go directly to the brain; the subject's natural eye-system could deteriorate completely, but the patient could still see. That technology, however, is far from being safe and efficient enough to be used mainstream right now. In my opinion, the next step down is a sub-retinal implant. While a more complicated surgery is required and a few more complication are possible, I believe "pound-for-pound", so to speak, it offers more results than implants on the retina do. It still uses the retina, making it so the patient does not have any external gear with the possibility of being lost or damaged by everyday activities.
Subretinal Implants
The subretinal implant strategy will likely work the best in the future. The subretinal implant avoids any form of wireless data complications, such as interference from other wireless devices and signals, or hacking, which has seemed to be a concern in class lately, because it does not use an external camera. Instead, it directly detect images and stimulates the photoreceptors in the retina so the images can be sent to the brain. Also, because all of the parts are within the body, there would be less parts of it to potentially lose (unlike the presumably expensive camera-containing glasses of the eprietinal device).
There are currently subretinal devices under testing that use the light received through the eye as a power source; though this currently is not the most powerful device by far compared to the exernally-powered epiretinal and subretinal devices, this particular subretinal device shows a lot of promise in that it would need to consist of one chip only, making for a simpler implanaion procedure and for an altogether less invasive device. Once technology improves enough, I believe that this subretinal implant will come out on top.
There are currently subretinal devices under testing that use the light received through the eye as a power source; though this currently is not the most powerful device by far compared to the exernally-powered epiretinal and subretinal devices, this particular subretinal device shows a lot of promise in that it would need to consist of one chip only, making for a simpler implanaion procedure and for an altogether less invasive device. Once technology improves enough, I believe that this subretinal implant will come out on top.
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