The retina is a thin layer at the back of your eye. Light lands on it, and it sends a picture of what you see to your brain. If the retina is hurt, the picture can go dark, blur, or get holes in it. Doctors use this word a lot; in ordinary talk people often just say “the back of the eye,” unless they mean this exact part. It is a body-part word, like iris or lens. The old name pictured it as a net, because the blood vessels there look like one — though actually, in class you only need the body meaning, not the history.