A group of inherited diseases that damage the light-sensitive rods and cones located in the retina, the back part of the eye. Rods, which provide side (peripheral) and night vision, are affected more than the cones, which provide colour and clear central vision. Signs of RP usually appear during childhood or adolescence. The first sign is often night blindness followed by a slow loss of side vision. Over the years, the disease will cause further loss of side vision. As the disease develops, people with RP may often bump into chairs and other objects as side vision worsens, and they only see in one direction – straight ahead. They see as if they are in a tunnel (thus the term tunnel vision).