Prosthetic retinas help blind mice see

Trials of prosthetic retinas in mice have given hope that people with vision loss due to retinal degeneration or damage could regain their sight.  Previous attempts at prosthetic retinas have only managed to relay simple pixilated shapes and patterns to the brain from the photoreceptors at the back of the eye.  The current research by Sheila Nirenberg and colleagues at Weill Cornell Medical College in New York has produced a visual information sent to the brain similar to that of healthy eyes.

When light enters a healthy retina it activates light-sensitive photoreceptors which process and send information to ganglion cells.  These cells transmit a pattern of electrical activity to the brain, which interprets the image.  Previous attempts at prosthetic retinas stimulate the ganglion cells directly.  However they don't use the patterns or "codes" that the cells use to send messages to the brain so only simple messages can be transmitted.

Nirenberg's team compared the signals going into healthy mice retinas with the output from ganglion cells, and produced an algorithm to recreate this "code".  Then using gene therapy they transfered the protein channelrhodopsin into the ganglion cells of blind mice, in order to make them responsive to light.  A computer processor, using Nirenberg's algorithm, encodes images from a tiny video campera imbedded into a pair of glasses rapid light pulses shone into the eye.

The ganglion cells treated with channelrhodopsin send signals to the brain in the normal way.  As the image is already "encoded" the brain sees a much more detailed image than images sent directly to the ganglion cells.  By analysing the  ganglion cell output from blind mice with prosthetic retinas compared to this of normally sighted mice it was shown that the output resembled each other, suggesting the technique presented a clearer image than old prostheics.

As people with retinal degeneration's retinas no longer send visual information to the brain, these prosethetics could be a way of restoring the sight of people with damaged retinas.  Though human trials have yet to be carried out, the research is an exciting prospect for many people suffering loss of vision due to retinal degerneration.

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