If science fiction technologies seem to you like the result of a rich imagination, you should know that one is already reality.

A more advanced "bionic eye" can now bring back vision to profoundly blind people.

A prototype has restored vision to six blind persons in 2002 and trials of the new retinal prosthesis will start soon. The new bionic eye could detect light, identify objects and even perceive motion.

One patient perceived the first images in 50 years, after losing sight due to retinitis pigmentosa, a hereditary condition. "We hoped they might get some sense of light and dark, but it's really amazing how much they can see, how the brain is able to fill in the gaps," says Mark Humayun, who carried out the implant surgery and developed the device with a team at Doheny Eye Institute at the University of Southern California, US.

The technique functions if the blind person still possesses some functional ganglion cells, nerve cells that pass visual signals from the retina to the optic nerve, as well an integer optic nerve. A minute electronic pad is put onto the retina, connecting its 16 electrodes with the ganglion cells. Each electrode signals to 20 to 30 cells.

A pair of glasses bears a wireless minicamera transmitting images to a cellphone-sized computer in the patient's pocket.

This wireless computer transmits the processed images to an electronic minireceiver implanted in the patient's head which passes them into electrical impulses to the ganglion cells and through the optic nerve to the brain's visual cortex. This process is extremely speedy, so the patient perceives the images in real-time; otherwise, the "vestibular-ocular reflex" would trigger dizziness and sickness.

The improved device will be checked on 50 - 75 subjects aged over 50, blinded by retinitis pigmentosa in a two years trial in five American centers.

The new device has 60 electrodes instead of 16 and the receiver is four times smaller, now fitting into the eye socket. The surgery will last 1.5 hours, down from 7.5 hours. "Currently recipients of the device experience a relatively narrow view, but more electrodes should provide a greater field of vision," Humayun says.

More stimulated ganglion cells means higher visual acuity. A third generation device will bear 1000 electrodes. "At the beginning, it was like seeing assembled dots, now it's much more than that," says Terry Bryant, aged 58, who received the implant in 2002 after 13 years of blindness. "I can go into any room and see the light coming in through the window. When I am walking along the street I can avoid low hanging branches and I can cross a busy street."

"If the trial is successful, the new device may be available commercially by 2009, priced around $30,000, similar to a cochlear implant", Humayun says.

Image credit: Mark Humayun