SAN FRANCISCO — A bionic eye that can restore sight to the blind should be available commercially within two years, scientists behind the revolutionary technology announced yesterday. The artificial retina has been cleared by US regulators to begin trials on between 50 and 75 people suffering from two of the most common causes of blindness, opening the way for millions more to benefit from similar implants in the future. If the research progresses well, a device could be on the market early in 2009 at a likely cost of about £15,000, said Mark Humayun, Professor of Ophthalmology at the Doheny Eye Institute, part of the University of Southern California. An early version of the prosthetic retina has already been fitted to six patients with retinitis pigmentosa, a degenerative and incurable eye condition that affects 1 in 3,500 people. All have recovered the ability to detect light and motion, and even to make out large letters and to distinguish between objects such as a cup, a knife and a plate. The second-generation device that is now starting trials should provide even better vision, as it contains 60 light-sensitive electrodes, compared with 16 in the previous model. […]