Retinal Implants Are Ray of Hope for the Blind
July 30, 2006
Twenty years ago, Hans-Joachim Sturm was told that he had retinitis pigmentosa. He didn't know what to think at first, but would soon become well acquainted with this eye ailment.
Retinitis pigmentosa is an incurable, hereditary disease that slowly kills the light-sensitive cells on the retina until the patient is left in darkness. Sturm is one of 40,000 sufferers of the disease in Germany.
"After a year, you see even less…"
"It goes slowly, with spurts of digression from time to time. For a long period, things stay the same and you don't notice anything and then, suddenly, what you were just recently able to see isn't there anymore. After a year, you see even less, and it continues like that," said 64-year-old Sturm.
First signs of the eye disease are a loss of color and contrast in the vision or night blindness.
Though the light-sensitive retinal cells die off, the nerve cells behind them, which transfer information to the brain, remain up to 30 percent intact. This means that if visual stimuli could circumvent the damaged retina, the patient would be capable of seeing again.
With this point in mind, researchers at the RWTH Aachen University of Technology developed a special device for sufferers of retinitis pigmentosa. The prosthetic consists of two parts: a high-tech pair of glasses and an implant that is surgically placed in the eye.
A tiny video camera is built into the glasses, along with an encoder that converts images into signals the nerves understand. The signals are then sent wirelessly to a receiver that has been implanted into the ocular lens.
The signals are then transferred to a micro contact film via a miniscule cable. These lie directly on the retina and stimulate with electrodes the nerve cells that lead to the optic nerve.
In this way, a person blinded by retinitis pigmentosa can see what the camera sees -- almost.
Not exactly 20-20
"The picture that the patient sees is very dim at the beginning," said Peter Walter from the University Clinic in Aachen. "But it can help a blind patient to differentiate between day and night, perhaps to get out of the way of large objects, circumnavigate obstacles, and recognize doors and windows.
Unfortunately, the implants cannot restore the ability to read or recognize faces, said Walter.
The resolution of the picture transferred through the device is dependent on the number of electrodes on the retina, which is limited to 200 to 300. Conducting more energy to the eye heats it up, which could cause complete damage.
As of yet, no solution has been found to counter this limitation. However, interest in retina implant research is strong and several research teams around the world are at work.
Next to Germany, research is most advanced in the US, especially at universities in Boston and Baltimore.
Similar to the German model, scientists at John Hopkins University in Baltimore are experimenting with the stimulation of nerve cells via short electronic impulses so that the brain can perceive pictures once again.
Experts at Boston's Harvard Medical School have developed an approach together with the Massachusetts Institute of Technology that could protect the eye from overheating: they are working on a film structure with micro contacts that can be placed between the light-sensitive cells on the retina and the nerve cells.
Broad application makes implants interesting
The US National Institute of Health has supported the research with more than $12 million so far. Interest is so high in the retinal implant project because it can be useful to more than just the relatively small number of retinitis pigmentosa patients.
"I can imagine that we might be able to help patients suffering from macula degeneration," said Wilfried Mokwa from the Aachen Institute for Electro-technology, referring to an age-related form of blindness that is much more common than retinitis pigmentosa.
But research still has a long way to go. The retinal implants are currently being tested on animals in Aachen and, if everything goes well, will be used by humans for the first time at the end of the year. Experts expect it to take five to seven years before the implants reach the market.