Progressive retinal atrophy (PRA) is a progressive, hereditary, nonpainful disease that eventually leads to complete loss of vision.  The clinical signs are often very similar in most affected breeds of dogs.  PRA always affects both eyes, and familiarity with your pets surroundings can often mask severe visual loss.  The earliest sign is decreased vision in dim light and darkness.  With progression of the disease, daylight vision is slowly lost as well.  Secondary cataract development is common in the advanced stages.  Most animals adapt well in a controlled environment.