Medical technology: The first commercial retinal implant is about to go on sale. It may be crude, but so were the first cochlear implants, 26 years ago

THAT it is possible to have a phone conversation with someone who is deaf shows just how far cochlear implants have come. Today's devices, which are routinely implanted, can stimulate the auditory nerve across a broad range of frequencies. This allows users to hear and understand speech in noisy environments, without needing to lip-read, and even to hear and appreciate music in many cases. But the earliest cochlear implants could do none of this; instead they merely provided some basic sounds to assist with lip-reading. Nevertheless, when they first received clinical approval, 26 years ago, they were hailed as a medical miracle. Now retinal implants are at a similar point, as the first such device is about to be granted clinical approval in Europe and will then go on sale.

The device, called the Argus II, is by no means a cure for blindness, says Robert Greenberg, the chief executive and co-founder of Second Sight, the company in Sylmar, California, that developed it. It is intended for use by people who have lost their sight as a result of retina-wasting diseases such as retinitis pigmentosa, and like the earliest cochlear implants it is designed to provide only some basic sensory assistance. But despite its limitations all 30 of the people who have received the Argus II as part of clinical trials can, at the very least, now see changes in light levels and detect objects. This means that they can navigate around obstacles, find doorways, see parked or moving cars and look at someone's head when talking to them. A handful of them can even read large print.

For the researchers who have spent many years developing these devices, and for the hundreds of thousands of blind people who stand to gain from them, the approval of the Argus II will mark an important turning-point. “The blind community have been waiting for this for decades,” says Lyndon da Cruz, a consultant retinal surgeon at Moorfields Eye Hospital in London, who has already implanted seven of the devices as part of the trials. “It's almost unbelievable that it's coming to market,” he says. “Very few people would have expected that there could be an artificial retinal device on the market by 2011.”

To get this approval Second Sight had to show that the benefits of the device outweighed the potential risks, says Dr Greenberg. The principles behind retinal implants are well established, he says. But it is one thing to build a prototype to demonstrate these principles and quite another creating a device that can be implanted for long-term use.

There are several different ways to build a retinal implant, but all of them use the same underlying mechanism. By electrically stimulating remaining healthy nerve cells in the retina using an electrode, sensations of light can be elicited in the person's visual field, thus mimicking the action of light-sensitive photoreceptors that were damaged by disease. The more electrodes you have, the more dots the person sees (the Argus II has 60). And so if you place enough of them in a rectangular array, and zap them according to signals fed wirelessly from a camera mounted in a pair of spectacles worn by the subject, blocky images start to take shape.

A number of research groups have demonstrated this over the past couple of decades, but until now none has managed to develop a retinal-array interface that could be left safely in the body, says Mr da Cruz. The problem is not simply that the interface might pose a risk to the patient—the device must also be robust enough to survive within the harsh environment of the body. Dr Greenberg likens it to designing a television set that can be thrown into the sea and will not only continue to work but will do so for decades to come.

Second Sight has succeeded by building on several decades of research into implantable devices and other neural interfaces, such as pacemakers and cochlear implants. The Argus I, Second Sight's first experimental prototype, actually used a signal processor originally designed for cochlear implants. (It had just 16 electrodes, was implanted in six patients and was never intended for market.) The company was founded in 1998 by Dr Greenberg and Sam Williams, an American philanthropist and engineer who suffered from retinitis pigmentosa and was frustrated by the slow pace of public research efforts. Sadly Dr Greenberg's co-founder died in 2009, just a year short of realising his goal of creating a commercial retinal implant.

But he leaves behind a legacy that will benefit thousands of people. The Argus II will initially be made available via hospitals in London, Manchester, Paris and Geneva, and—once it receives approval from the Food and Drug Administration—in America. Second Sight expects about 100 devices to be implanted in its first year on sale; with a price tag of $100,000 only a limited number of people will be able to afford it. This may seem steep, says Dr Greenberg, but it's similar to what the first cochlear implants cost. As government reimbursement schemes kick in, the device should become more affordable and widely available, he says.

And as more people receive the device, the technology should improve, says Mr da Cruz. The trials so far have shown that, for reasons that remain unclear, some patients appear to benefit more than others from the device. As it becomes more widespread, the reasons for this should become clear.

Looking further ahead, Second Sight is already conducting animal trials on the Argus III, which is expected to have several hundred electrodes. Other researchers are also working on similar technologies, including Eberhardt Zrenner, director of the Institute for Ophthalmic Research at the University of Tübingen in Germany. Dr Zrenner's company, Retina Implant, is developing a device which contains the camera within the eye and has more than 1,500 electrodes.

Natural vision is extraordinarily powerful, so it is unlikely that implants will ever be able to offer anything quite as rich, says Mr da Cruz. But as cochlear implants have shown, the technology that first reaches the market is very different from what is available 20 years later. As the number of electrodes increases and signal-processing software improves, it is not unthinkable to imagine a blind person in 2037 reading an article marvelling at how far the technology has come.