Retinal Microchip in
Clinical Trials

With bioelectronics, the blind patient wears light-weight glasses equipped with a tiny camera in the lense. The glasses are connected by wire to a visual processing unit and battery which sits outside the patient's body (usually clipped to their belt).

An image is picked up by the camera in the glasses, sent to the processor, then wirelessly sent on to an electronic microchip implanted on the retina. The retinal microchip (or "receiver") stimulates the nerve cells in the retina which are then "jump started" and able to send an image back to the brain via the optic nerve.

All of this, of course, happens instantaneously so that the patient is able to see images in real time rather than delayed.

The microchip itself is not at all like the microchips you've seen for computers or cell phones. The chip is really more like a tiny, thin band aid which is placed as close to the retina as possible and made of a material more similar to seran wrap than plastic or metal.

The first big challenge the researchers had to overcome was power. How can you create a stable and efficient power source for such a small implant? They tried to create a solar-powered implant but found that in order to get the amount of power they needed into such a small space they would need the equivalent power of ten suns!

Well, that just wouldn't do. So the power for the chip is now located outside the body. This is much better because size is not as much a factor (it doesn't need to fit into the eye) and it's much safer (no more worries about a leaking power source in the body). Also, it's easy to recharge or replace.

Another issue was longevity. If you're going to get your eye cut open and a chip implanted you're going to want it to last! The new chips are expected to last a decade and are customized to each patient. Also, since the processing unit is located outside the body it's easy to replace or upgrade the system without having to endure more surgery.

Finally, this sort of device, at least at this point, really only works with certain types of retinal degenerative diseases, such as Retinitis Pigmentosa and Leber's Congenital Amaurosis.

Hearing that the chip is meant to "jump start" existing retinal nerve cells may make you wonder how it works in patients who are already completely blind. If the retina is so damaged that it isn't even picking up light, then is there anything there for the chip to jump start?

Dr. Humayun explained that even in end stage retinal dystrophy where the patient has no light perception at all research shows that at least 80% of bipolar cells and 30% of ganglion cells are still intact in the inner recesses of the retina. So there is something there to work with!

However, he also pointed out that as the retina degenerates, these nerve cells rearrange themselves and become rewired. The microchip targets the ganglion nerve cells because it seems that these cells maintain a more direct hardwire to the brain.

Although this is good news, it does still mean that the patient's optic nerve and visual cortex will need to be healthy and able to send and pick up visual signals. The microchip also does not work in patients with detached retinas.

The first microchips (called Argus I) were implanted in patients with bare to no light perception and who had been blind for multiple decades. The first device was equipped with sixteen electrodes and the visual acuity of the patients after implantation was measured at about 20/2400. That's not that great considering that legally blind acuity starts at a mere 20/200, but then again these patients were completely blind to begin with!

Visual acuity was measured by having patients look at a computer screen with long black stripes on a white background. The researchers would check how thick the stripes had to be before the patient could see them (the thicker the stripes, the worse the visual acuity) and then they would move the stripes about (placing them horizontally, vertically, or diagonally) and check if the patient could differentiate the direction of the lines.

The next step was to check that the number of electrodes was really making a difference in the measurement of visual acuity, so the team implanted microchips with only four electrodes and the visual acuity dropped to 20/8000.

So in 2007 the team developed the Argus II, a chip with sixty electrodes. This trial is still in progress so we don't have accurate visual acuity measurements for it, but one patient who has been blind for twenty-five years reports that she can now play basket ball with her grandson and see the basket ball hoop!

The images the patients see should translate into the brain as a series of dots (where the electrodes have fired and sent signals to the nerve cells) but researches think that the brain itself is filling in a lot of the missing information.

Within the next five to seven years the team plans to implant a device with 240 and then 1000 electrodes. They hope to see a measured visual acuity of 20/200!