Progressive retinal Atrophy, cone-Rod dystrophy 4 (PRA-crd4) is an inherited eye disease affecting Beagles. PRA-crd4 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. Affected dogs can show symptoms of vision loss or have signs of retinal disease on veterinary ophthalmologic exam by 3 years of age. However, age of onset varies significantly in PRA-crd4 affected dogs, and has been reported from 1 to 15 years of age. Mutations in the RPGRIP1 gene show Incomplete Penetrance, meaning that not all dogs inheriting two copies of the Mutation develop clinical disease. This suggests that other unknown genetic or environmental factors may play a role in modifying disease development and progression. Although progression tends to be relatively slow, most affected dogs (especially those with an early age of disease onset) will progress to complete blindness.