Three blind patients have been able to see shapes and objects just days after doctors implanted electronic chips in the backs of their eyes.

The study's results raise hope for the thousands of people who have gone blind because of degenerative eye diseases like retinitis pigmentosa.

Researchers in Germany surgically implanted a tiny electronic microchip under the retinas of three patients who were blind due to hereditary retinal degeneration. Previously, all three had good central vision.

The illustration shows the position of the implant chip, the square device marked with a C, under the retina. ((Courtesy of the authors))

The tiny implants do the work of the eye's light receptors that have been destroyed by disease. Each implant contains 1,500 light sensors, which are connected to amplifiers and electrodes.

Electric impulses are relayed to the optic nerve behind the eye. The implants are powered externally by a control unit that is connected to the chip by a silicone cable that emerges behind the ear.

Within days of having the implants, three previously blind patients could locate bright objects placed on a dark table. Two could also make out patterns.

One patient could describe and name objects like cutlery or differing kinds of fruit. He could also locate people while walking around a room, and read large letters and words — this after years of blindness.

Th authors say their approach differentiates itself from other types of retinal implants, which require patients to carry an external camera.

"The advantage of our approach is that all parts of the device can be implanted invisibly in the body, that inner processing can be used, and that a continuous, stable image with unmatched spatial resolution is perceived," the authors write.

"The results of this pilot study provide strong evidence that the visual functions of patients blinded by a hereditary retinal dystrophy can, in principle, be restored to a degree sufficient for use in daily life."

The study is published in the latest issue of Proceedings of the Royal Society B journal.

Further clinical trials are planned and a follow-up study — using an upgraded power system for the chip — is already underway.