After decades of development and years of clinical trials, an optical prosthesis capable of restoring at least partial vision to those suffering from retina-damaging diseases will hit the market. Second Sight Medical Products, Inc., said Wednesday that its Argus II Retinal Prosthesis System has been approved for sale throughout most of Europe. Sylmar, Calif.–based Second Sight is planning to apply for U.S. Food and Drug Administration (FDA) approval this year.

The retina lines the back of the eye's inner surface and records images in patterns of light and color. The Argus II implant actually relies on a mini camera mounted on a pair of sunglasses to capture an image and send the information to a video processor, worn on the belt along with a wireless microprocessor and battery pack. After the video processor converts the images to an electronic signal, a transmitter on the glasses sends that information wirelessly to the receiver implanted under the eyeball's clear mucus membrane, called the conjunctiva.  The receiver in turn conveys the signals through a tiny cable to an electrode array placed on the retina. The array directly stimulates the cells that lead to the optic nerve.

On receiving the pulses, the brain perceives patterns of light and dark spots corresponding to the electrodes stimulated. Patients learn to interpret the visual patterns produced into meaningful images.

Second Sight received the go ahead to make the Argus II available based on a successful clinical trial with 30 blind patients worldwide. The retinal implant will first be available later this year at Centre Hospitalier National d'Ophthalmologie des Quinze-Vingts in Paris, Geneva's Hôpitaux Universitaires de Genève, England's Manchester Royal Eye Hospital and Moorfields Eye Hospital in London. It costs $100,000 per implant, although the company also says it is trying to have all or part of the cost subsidized in some countries.

Other retinal prostheses are expected to follow, in particular a subretinal device from Germany's Retina Implant, AG, that places the implant under the surface of the retina to stimulate bipolar cells. Three previously blind patients suffering from retinitis pigmentosa and other ocular diseases were fitted with the company's retinal implants and have been able to locate bright objects on a dark table, a team of researchers led by Eberhart Zrenner, the company's co-founder and director and chairman of the University of Tübingen's Institute for Ophthalmic Research in Germany, reported recently in Proceedings of the Royal Society B. One of the patients was able to correctly describe and name objects like a fork or knife on a table, geometric patterns, different kinds of fruit and discern shades of grey with only 15 per cent contrast.

Images courtesy of Second Sight Medical Products, Inc.