Retinal prostheses for restoration of sight to patients blinded by retinal degeneration are being developed by a number of private companies and research institutions worldwide. The system is meant to partially restore useful vision to people who have lost their photoreceptors due to retinal diseases such as retinitis pigmentosa (RP) or age-related macular degeneration (AMD). Three types of retinal implants are currently in clinical trials: epiretinal (on the retina), subretinal (behind the retina), and suprachoroidal (between the choroid and the sclera). Retinal implants introduce visual information into the retina by electrically stimulating the surviving retinal neurons. So far, elicited percepts had rather low resolution, and may be suitable for light perception and recognition of simple objects. History Foerster was the first to discover that electrical stimulation of the occipital cortex could be used to create visual percepts, phosphenes. The first application of an implantable stimulator for vision restoration was developed by Drs. Brindley and Lewin in 1968. This experiment demonstrated the viability of creating visual percepts using direct electrical stimulation, and it motivated the development of several other implantable devices for stimulation of the visual pathway, including retinal implants. Retinal stimulation devices, in particular, have become a focus of research as approximately half of all cases of blindness are caused by retinal damage. The development of retinal implants has also been motivated in part by the advancement and success of cochlear implants, which has demonstrated that humans can regain significant sensory function with limited input. The Argus II retinal implant, manufactured by Second Sight Medical Products received market approval in the US in Feb 2013 and in Europe in Feb 2011, becoming the first approved implant. The device may help adults with RP who have lost the ability to perceive shapes and movement to be more mobile and to perform day-to-day activities. The epiretinal device is known as the Retina Implant and was originally developed in Germany by Retina Implant AG. It completed a multi-centre clinical trial in Europe and was awarded a CE Mark in 2013, making it the first wireless epiretinal electronic device to gain approval. Candidates Optimal candidates for retinal implants have retinal diseases, such as retinitis pigmentosa or age-related macular degeneration. These diseases cause blindness by affecting the photoreceptor cells in the outer layer of the retina, while leaving the inner and middle retinal layers intact. Minimally, a patient must have an intact ganglion cell layer