"Retinitis pigmentosa (RP) is the name given to a group of inherited eye conditions called retinal dystrophies."
"A retinal dystrophy such as RP affects the retina at the back of your eye and, over time, stops it from working. This means that RP causes gradual but permanent changes that reduce your vision. How much of your vision is lost, how quickly this happens and your age when it begins depends on the type of RP that you have. The changes in your vision happen over years rather than months, and some people lose more sight than others."
Living with RP - Dave's Story - RNIB Series