Actually, retinitis pigmentosa (RP) is not one single eye disease, but a collective name for a large group of hereditary retina disorders. Most people suffering from RP will become night-blind, develop tunnel vision and their eyesight deteriorates.
The name retinitis pigmentosa refers to the accumulation of pigment in the retina. With RP the light-sensitive cells, the photoreceptors, in the retina slowly die. These are the rods and the cones. The rods are found in the outer part of the retina and most cones are found in the central part.
About 4000 people in the Netherlands suffer from retinitis pigmentosa. 800 to 1000 people of this group suffer from Usher Syndrome (RP with loss of hearing).