Excerpt from a lecture given by Hugh Darrow at Harvard University in August 2008.
Today's retinal implants are deisgned to partially restore useful vision to people who have lost their sight due to degenerative eye conditions. The device consists of an electrode array attached to the eye's retina; a digital camera worn on the user's body (usually attached to a pair of glasses); and a transmitter and receiver that converts images to electrical impulses. These impulses are then transmitted by radio frequency to the electrode array.
At the moment, there are two types of retinal implants available: epiretinal implants and subretinal implants. The only difference between the two is at what point the electrode array stimulates the cells that would attach to photoreceptors. The signal transmitted travels to the optic nerve and then to the brain, allowing for the perception of sight. However, the vision a person receives from these implants is very rudimentary. He or she may be able to see an image similar to a scoreboard made up of large lights, or detect something come from light that is only an arm's length away.
In other words, today's retinal implant gives the patient very limited vision. For a person who is going blind, it's a very good option for retaining some sense of vision. Still, we at Darrow Industries intend to improve it.