The Artificial Retina Project has a graphic that explains how a retinal implant works to restore some vision in people with certain kinds of blindness.
TeachEngineering has a lesson plan, Biomedical Devices for the Eyes, that provides background information on eye problems and vision deficiencies. The lesson plan introduces students to a variety of biomedical devices, including retinal implants.
The Scientist provides a series of short articles that offer a general overview of retinal implant devices.
Bionic Vision Australia is a national consortium of researchers working together to develop a bionic eye to restore vision to people with retinitis pigmentosa and age-related macular degeneration.
The article, "Bionic Senses" from Harvard University, provides background information about how neuroprosthetics can help restore sight and hearing through the use of cochlear and retinal implants.