Retinitis pigmentosa commonly runs in families. The disorder can be caused by a number of genetic defects. The cells controlling night vision (rods) are most likely to be affected. However, in some cases, retinal cone cells are damaged the most. The main sign of the disease is the presence of dark pigmented spots in the retina. As the disease gets worse, peripheral vision is gradually lost. The condition may eventually lead to blindness, but usually not complete blindness. Signs and symptoms often first appear in childhood, but severe visual problems do not usually develop until early adulthood. The main risk factor is a family history of retinitis pigmentosa. It is an uncommon condition affecting about 1 in 4,000 people in the United States.
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