Retinal prosthesis restores degree of sight to the blind

Researchers at the University of Southern California report that an intraocular retinal prosthesis developed by Second Sight LLC may restore some degree of sight to the blind.

Initial results of an intraocular retinal prosthesis trial indicates the implant may restore some degree of sight to the blind, according to researchers at the Keck School of Medicine of USC and the Doheny Retina Institute.

‘We have successfully completed enrolment and implantation of three patients in the trial,’ said Mark Humayun, professor of ophthalmology at the Keck School.

‘And we have found that the devices are indeed electrically conducting and are giving the patients the ability to detect light or even to distinguish between objects such as a cup or plate,’ Humayun said.

The results of the US Food and Drug Administration approved feasibility trial were presented at the annual meeting of the Association for Research in Vision and Ophthalmology (ARVO), held in Fort Lauderdale, Florida.

The microelectronic prosthesis used in this first phase of the trial was intended to stand in for the damaged retinal cells in people suffering from blinding diseases as retinitis pigmentosa and macular degeneration.

The implant measures four millimetres by five millimetres and is studded with 16 electrodes in a four-by-four array. The device has been developed by Valencia, California-based Second Sight LLC.

The first patient in the trial underwent surgery to receive the implant in February 2002. The second patient received an implant in July 2002, whilst the third patient underwent surgery in March 2003.

The prosthesis – a sliver of silicone and platinum – is attached to the top of the retina. It is said to work by electrically stimulating the remaining healthy retinal cells via the array of electrodes. The retinal cells, in turn, pass on the visual information to the brain via the optic nerve.

Initial tests in the three implanted patients have shown that they can perceive light on each of the 16 electrodes and that the prosthesis has continued to function as expected.

More advanced testing revealed that patients with the microelectronic implant are capable of detecting when a light is turned on or off, describing the motion of a point of light, and even recognising and counting discrete objects.

The first tests of the prosthesis in all three patients involved computer-generated points of light sent directly to the implant, said Humayun.

Over time, they were ‘graduated’ to images received by an external video camera.

These images are sent to the intraocular electrode array attached to the retina through a receiver that is implanted behind the patient’s ear during the implant surgery. The signal then is re-created by stimulating the appropriate electrodes in the prosthesis.

Testing on the three patients is ongoing, said Humayun.

‘We are now looking at how useful the prosthesis can be in activities of daily living,’ he said. ‘We’re planning on doing some mobility testing to see if the prosthesis provides enough vision to allow patients to navigate through a room.’