News feature
Retinal implant lets blind see light

There has been a major breakthrough for people suffering from Retinitis Pigmentosa (RP), a disease which causes the degeneration of photoreceptor cells in the retina and ultimately leads to blindness. A California, United Statesbased company, Second Sight has developed an electronic retinal implant – the Argus II Retinal Prosthesis System – that has the potential to bring light back to blind individuals with RP.

The company announced in January that they had received US Food and Drug Administration approval to conduct a clinical study of the Argus II Retinal Prosthesis System.

“This is a major milestone not only for the company but, more importantly, for RP patients who have little in the way of hope and treatment options,” said Robert Greenberg, MD, PhD, president and CEO of Second Sight, and a leader in the field of retinal prostheses for over 15 years. “We have put together an outstanding group of clinical investigators and study sites around the country, and worldwide.”

Greenberg described the prosthesis at the at the Cannes Retina Festival 24th Annual Meeting of the American Society of Retina Specialists (ASRS) & 6th Annual Meeting of the European Vitreoretinal Society (EVRS), held in Cannes, France, last year. He said five patients implanted with the device between 2002 and 2004 continue to use it daily.

“These patients are using the prosthesis to perform tasks such as finding doorways, following the action in sporting events, navigating, following individuals, locating objects across the room and eating,” he said.

“Every patient is able to perceive discrete phosphenes and also perform visual spatial tasks. There have been no significant adverse events such as infections or retinal detachments, and equally as important, there have been no device failures over the four years,” he said.

He said the concept behind the implant is that by electrically stimulating the residual nerve cells in the retina, you can create perceptions of light that lead to image perception. The firstgeneration prosthesis has 16 independently controlled electrodes, so there are 16 individual contacts that may be activated. The array can produce visual percepts at charge densities within the safety limits for platinum electrodes.

The implant that has been approved for clinical trials is the second generation Argus II Retinal Prosthesis System, which is designed with 60 independently controllable electrodes, which should provide implanted subjects with higher resolution images. The array of electrodes are attached to the retina and used in conjunction with an external camera and video processing system on a pair of glasses to provide a rudimentary form of sight to implanted subjects.

“This advanced artificial retina technology holds promise for providing even better detailed vision than the original device,” says Stephen Rose, PhD, chief research officer, Foundation Fighting Blindness. “The opportunity for restoring some functional vision is a very exciting prospect for people who are blind or have substantial vision loss.”

The multicentre study, which will start this year in the United States, will be conducted in subjects who:

- Have a confirmed history of RP with remaining visual acuity of bare light perception or worse in both eyes with functional ganglion cells

- Have a history of former useful vision

The study will require each subject to be followed for at least three years with visits to the implanting centre up to two times per week.

                                  
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