Using light-sensitive microchips implanted in the inner surface of the eye, scientists are continuing to restore some vision to blind patients — for instance, helping them recognize facial expressions such as smiles.
The visual sharpness of the new devices surpasses the highest resolution of any other visual implant so far, researchers added.
"One guy was able to see his fiancée in the face — it may have been a ghostly picture, but he was very, very happy. It was a special moment for him," researcher Eberhart Zrenner, a neuro-ophthalmologist at the University of Tuebingen in Germany, told LiveScience.
The implant, named the Alpha-IMS, is only about 3 millimeters long by 3 millimeters wide, and less than 100 microns thick, making it thinner than the average diameter of a human hair. Despite its tiny size, the microchip is loaded with 1,500 light detectors, which transmit electrical impulses through a patient's nerves to generate a colorless 1,500-pixel image. In contrast, other visual implants provide images with significantly less than 100 pixels. [ See Images of the Eye Implant ]
The implant is placed under the retina, the inner lining of the eye. The device essentially replaces degenerated light-sensitive rod and cone cells of patients suffering from diseases such as retinitis pigmentosa, a group of inherited diseases that afflict 1 in 4,000 people across the world.
A wire trails from inside the eye to its edge and then under the skin to a point behind the ear, where patients can place a control box to wirelessly supply power. Patients can also use the control box to adjust the brightness and contrast of images.
"The fact that the chip is in the eye means that vision moves with the eye," Zrenner added. "Cosmetically, you also cannot see the implant from the outside." Other electronic approaches to restoring vision typically involve bulky glasses containing cameras, and the field of vision depends on where the cameras are pointed, not where the eyes look.
In the first study with the implant, detailed in 2010, the device could help patients read the hands of a clock, discern seven shades of gray, find tableware, identify apples and bananas, and combine the letters of the alphabet to form words. However, most of the 11 patients given the implant did not achieve these results, partly because researchers were still refining where best to implant the device and learning which patients might benefit most.
In the latest human clinical trial with these chips, nine German patients were tested in the laboratory as well as outdoors and at home during a three-to-nine-month period. The device restored functional vision for most of the patients — for instance, eight could perceive light, seven could tell where light was coming from and five could detect motion. The success of this latest clinical trial is largely due to the researchers now knowing to place the implant under the fovea, a spot near the center of the retina that is responsible for the center of the field of vision.
"The results of our first human clinical trial exceeded our expectations, and we are further encouraged by the results from the second human trial," Zrenner said.
Moreover, visual sharpness for two of the patients surpassed acuity seen in the first clinical trial. Three were able to read letters spontaneously. In addition, in and outside the laboratory, five patients reported the ability to recognize facial characteristics such as the presence or absence of eyeglasses, as well as distinguish objects such as telephones, read signs and find doorknobs, see where plates and cutlery were on tables and tell red wine from white wine. Patients described blurry, flickering images of the world in gray tones, reminiscent of unfocused images from an older black-and-white television set. [ Eye Tricks: Gallery of Visual Illusions ]
"This may not help much, but this produces a big difference for a blind person," Zrenner said.
Zrenner cautioned that not allblind patients would benefit from this device. For example, it will not help in cases where the optic nerve or brain damage is involved, or where the retina is ruined or has insufficient blood flow.
The researchers would now like to improve the durability of the implant against the corrosion it can experience. "It's a challenge working with something that thin, to protect it against water and ions in the eye," Zrenner said. "We're in a situation like that of the first airplanes, which were made of wood and paper, more or less. We now have to work on materials science a lot, since the body is a hostile place for electronics."
Future research may also expand the visual field of patients. "We can put two or three chips next to each other — we may get wide-screen vision," Zrenner said.
Zrenner helped found Retina Implant AG in Germany, which manufactures the implants.
"As a leading relevant patient organization in the United Kingdom, we have been watching Retina Implant AG's research with great interest," David Head, CEO of RP Fighting Blindness, said in a statement. "The results published today show definite promise to one day restore functional vision to patients with advanced-stage retinitis pigmentosa."
Clinical studies of the implant are also taking place in England and Hong Kong. The researchers are currently attempting to get regulatory approval to begin clinical trials in the United States and Europe as well.
The scientists detailed their findings online Feb. 20 in the journal Proceedings of the Royal Society B: Biological Sciences.