Progressive Retinal Atrophy, PRA4 (Lhasa Apso Type) is an inherited eye disease affecting dogs. Progressive Retinal Atrophy, PRA4 (Lhasa Apso Type) occurs as a result of degeneration of both Rod and cone type Photoreceptor Cells of the Retina, which are important for vision in dim and bright light, respectively. Age of onset is difficult to determine as the disease is progressive and owners may remain unaware of a clinically affected dog. The rod type cells are often first to degenerate and affected dogs will have vision deficits in dim light (night blindness) and loss of peripheral vision. Over time affected dogs continue to lose night vision and begin to show visual deficits in bright light. Other signs of progressive retinal atrophy involve changes in reflectivity and appearance of a structure behind the retina called the Tapetum that can be observed on a veterinary eye exam. Genetic testing may help clarify if a dog is affected with progressive retinal atrophy or another inherited condition of the eye.