Progressive retinal Atrophy, PRA3 is a late-onset inherited eye disease affecting Tibetan terriers. Progressive retinal atrophy (PRA) 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. In general, the rod type cells are affected first and affected dogs will initially 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. The reported average age of clinical diagnosis in dogs affected with this type of PRA is about 5 years of age.