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Health

Bionic Eye Lets Blind See

NeuroskepticBy NeuroskepticNovember 5, 2010 5:45 PM

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No, really. Read all about it in a remarkable (if awkwardly named) new paper from German team Zrenner et al, Subretinal electronic chips allow blind patients to read letters and combine them to words.

The device acts as an artificial retina. It's a tiny 3 x 3.1 mm panel (about ? that size) containing an array of 1,500 individual light-sensitive microphotodiodes (38 x 40).

Each sensor converts incoming light into an electrical current - the brighter, the stronger - and outputs it through a tiny electrode. These currents stimulate nerve cells in the retina, in the same way that the eye's own photoreceptor cells normally do.

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Of course, for this to be useful, you need to have a retina with functioning nerve cells, an intact optic nerve to convey the information to the brain, and working visual brain areas. This means that the technology is only useful for certain kinds of blindness caused by damage to photoreceptor cells. However, such blindness is quite common; retinitis pigmentosa, a genetic disorder, is one such.

Did it work? Yes. The chip was implanted in three patients, all of whom had been born sighted but had become almost completely blind due to retinal degeneration. In all three patients, the chip restored some degree of vision.

However, the benefits were most dramatic in Patient 2. He gained the ability to recognise everyday objects like spoons, bananas, and apples; he could read a clock to tell the time; and he could read letters (albeit special, extremely large letters about 8 cm high). "YouTube or it didn't happen?" Here you go...

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The subretinal implant is not the only bionic eye idea in town, however. There have been various attempts to provide the blind with surrogate vision, like the camera attached to the tongue. Other researchers have been working on using - effectively - an external ("epiretinal") camera, which then interfaces with the optic nerve to transmit information to the brain.

However, Zrenner et al say that their method is better. Well, they would, but they make a good case. With an epiretinal device, you need to process the information into a form which the brain can recognise, but even after doing so, it takes some "getting used to".

Patients in this study were immediately able to make sense of what they saw, because the implant works much like a healthy retina. Also, epiretinal approaches have so far only provided up to 60 pixels.

Still, the chip has limitations. The image is greyscale, much less detailed than normal vision (38x40 pixels - an iPhone has 960x640), and being tiny, it only covers a small fraction of the normal visual field - although given that all detailed vision takes place in a tiny part of the retina called the fovea, this is not as much of a limitation as it first appears so long as you implant the chip where the fovea used to be; notably, this is what they did for Patient 2.

The chip also requires an external power supply, meaning that patients need to carry a battery pack around, and of course, they have a fairly hefty wire coming out of the side of their head. But really, that's not that important because this is a frickin' bionic eye, and it actually works.

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Eberhart Zrenner, et al. (2010). Subretinal electronic chips allow blind patients to read letters and combine them to words Proc. R. Soc. B : 10.1098/rspb.2010.1747

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