Progressive retinal Atrophy (bullmastiff/mastiff type) is an inherited eye disease affecting bullmastiffs and mastiffs. Progressive retinal atrophy (bullmastiff/mastiff type) occurs as a result of degeneration of Rod type Photoreceptor Cells of the Retina, important for vision in dim light. Initial clinical 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. Affected dogs initially present by 18 months of age with vision loss in dim light (night blindness) and loss of peripheral vision. The visual deficits gradually progress to complete vision loss. Dogs that inherit two RHO mutations have a more rapid disease progression than dogs that have only inherited one Mutation. The disease follows a variable progression and severity depending on the individual, but complete degeneration of the retina can take years.