Progressive Retinal Atrophy (Shetland Sheepdog Type) affects dogs and is an adult-onset inherited eye disease. 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 will 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 5 years of age. However, this PRA type appears to have a wide range in age of onset with reports of clinical diagnosis from 2 to 11 years of age. Progressive Retinal Atrophy (Shetland Sheepdog) is characterised by visual impairment due to degeneration of the photoreceptors in the retina, usually leading to blindness. The disease can be subdivided by age at onset and rate of progression.