What causes them?
The diseases are inherited. This means that you are born with the specific genetic anomaly that results in an abnormality of photoreceptor cells causing the cells in the retina to not work correctly. The retina is the light-sensitive tissue at the back of the eye that senses and transmits light signals to the brain through the optic nerve to form images, enabling people to see.
Researchers have found over 300 genes that cause inherited retinal diseases. Some inherited retinal diseases, such as choroideremia or X-linked retinoschisis are caused by one or only a small number of genes. Other diseases can be caused by many different mutations in many different genes. For example, over 64 genes have been identified that cause retinitis pigmentosa. In addition, for many people, the gene variation that causes their inherited retinal disease has not been identified yet.