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Prosthetic retina helps to restore sight in
mice
Scientists crack the code that tells the brain what the eye
has seen.
Two neuroscientists have created a prosthesis that can partially restore
the sight to blind mice. The device could eventually be developed for use in
humans.
More than 20 million people worldwide become blind owing to the
degeneration of their retina, the thin tissue at the back of the eye that
turns light into a neural signal. Only one prosthesis has been approved for
treatment of the condition — it consists of an array of surgically implanted
electrodes that directly stimulate the optic nerve and allow patients to
discern edges and letters. Patients cannot, however, recognize faces or
perform many everyday tasks.
Sheila Nirenberg, a physiologist at the Weill Medical College at Cornell
University in New York thinks that the problem is at least partially down to
coding. Even though the retina is as thin as tissue paper, it contains
several layers of nerves that seem to encode light into neural signals. "The
thing is, nobody knew the code," she says. Without it, Nirenberg believes
that visual prostheses will never be able to create images that the brain
can easily recognize.
Now, she and her student, Chethan Pandarinath, have come up with a
code and developed a device that uses it to restore some sight in blind
mice.
The duo began by injecting nerve cells in the retinas of their mice with a
genetically engineered virus. The virus had been designed to insert a gene
that causes the cells to produce a light-sensitive protein normally found in
algae. When a beam of light was then shown into the eye, the protein
triggered the nerve cells to send a signal to the brain, performing a similar
function to healthy rod and cone cells.
A prosthetic retina that can translate an image into
neural signals was tested using a picture of a baby's
face. A is the original image. B is the image after it
passes through the coding software. C is after it has
been processed by the retinal cells. D is the processed
image without coding.
Coded vision
Earlier efforts had managed to get this far, but Nirenberg and Pandarinath
went a step further. Rather than feeding visual signals directly into the
eye, they processed them using a code that the pair had developed by
watching how a healthy retina responds to stimuli. After receiving the
encoded input, the mice were able to track moving stripes1, something
that they hadn't been able to do before. The pair then looked at the neural
signals that the mice were producing and used a different, 'untranslate',
code to figure out what the brain would have been seeing. The encoded
image was clearer and more recognizable than the non-encoded one (see
image).
The importance of encoding has been debated among scientists working on
visual prostheses, says James Weiland, an ophthalmologist at the University
of Southern California in Los Angeles. Some think that it will be crucial, but
others think the brain can adapt to an unprocessed signal. Nirenberg and
Pandarinath have shown that encoding provides an advantage, he says,
but how effective it is won't be known until the technique is tried out in
people. "You can't say for sure until you have the patient telling you 'yes I
see it. It's better when you do that'," he says.
Nirenberg hopes to test the system in human trials soon. The encoding is
simple enough to be done by a microchip, which, together with a small
video camera could fit onto a pair of glasses. The camera would record a
signal and the encoder would then flash it directly onto the genetically
treated nerve cells in the eye. If it works, the technique is simple enough
that it could be done in a doctor's office. "We would like to [try it] in
patients in the next one or two years," she says.
http://www.nature.com/news/prostheti...n-mice-1.11164
mice
Scientists crack the code that tells the brain what the eye
has seen.
Two neuroscientists have created a prosthesis that can partially restore
the sight to blind mice. The device could eventually be developed for use in
humans.
More than 20 million people worldwide become blind owing to the
degeneration of their retina, the thin tissue at the back of the eye that
turns light into a neural signal. Only one prosthesis has been approved for
treatment of the condition — it consists of an array of surgically implanted
electrodes that directly stimulate the optic nerve and allow patients to
discern edges and letters. Patients cannot, however, recognize faces or
perform many everyday tasks.
Sheila Nirenberg, a physiologist at the Weill Medical College at Cornell
University in New York thinks that the problem is at least partially down to
coding. Even though the retina is as thin as tissue paper, it contains
several layers of nerves that seem to encode light into neural signals. "The
thing is, nobody knew the code," she says. Without it, Nirenberg believes
that visual prostheses will never be able to create images that the brain
can easily recognize.
Now, she and her student, Chethan Pandarinath, have come up with a
code and developed a device that uses it to restore some sight in blind
mice.
The duo began by injecting nerve cells in the retinas of their mice with a
genetically engineered virus. The virus had been designed to insert a gene
that causes the cells to produce a light-sensitive protein normally found in
algae. When a beam of light was then shown into the eye, the protein
triggered the nerve cells to send a signal to the brain, performing a similar
function to healthy rod and cone cells.
A prosthetic retina that can translate an image into
neural signals was tested using a picture of a baby's
face. A is the original image. B is the image after it
passes through the coding software. C is after it has
been processed by the retinal cells. D is the processed
image without coding.
Coded vision
Earlier efforts had managed to get this far, but Nirenberg and Pandarinath
went a step further. Rather than feeding visual signals directly into the
eye, they processed them using a code that the pair had developed by
watching how a healthy retina responds to stimuli. After receiving the
encoded input, the mice were able to track moving stripes1, something
that they hadn't been able to do before. The pair then looked at the neural
signals that the mice were producing and used a different, 'untranslate',
code to figure out what the brain would have been seeing. The encoded
image was clearer and more recognizable than the non-encoded one (see
image).
The importance of encoding has been debated among scientists working on
visual prostheses, says James Weiland, an ophthalmologist at the University
of Southern California in Los Angeles. Some think that it will be crucial, but
others think the brain can adapt to an unprocessed signal. Nirenberg and
Pandarinath have shown that encoding provides an advantage, he says,
but how effective it is won't be known until the technique is tried out in
people. "You can't say for sure until you have the patient telling you 'yes I
see it. It's better when you do that'," he says.
Nirenberg hopes to test the system in human trials soon. The encoding is
simple enough to be done by a microchip, which, together with a small
video camera could fit onto a pair of glasses. The camera would record a
signal and the encoder would then flash it directly onto the genetically
treated nerve cells in the eye. If it works, the technique is simple enough
that it could be done in a doctor's office. "We would like to [try it] in
patients in the next one or two years," she says.
http://www.nature.com/news/prostheti...n-mice-1.11164
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