Progressive retinal atrophy (PRA) is a group of genetic iseases seen in certain breeds of dogs and, more rarely, cats. It is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trait, with the exception of the Siberian Husky (inherited as an X chromosome linked trait) and the Bullmastiff (inherited as an autosomal dominant trait). There is no treatment. PRA is similar to retinitis pigmentosa in humans.