Progressive Retinal Atrophy (also known as “PRA”) is a group of inherited diseases that cause degeneration of the retina in dogs and results in permanent blindness. The retina is a thin layer of nervous tissue that lies in the back of the eye and is responsible for converting light into electrical impulses. The electrical impulse is then transmitted along the optic nerve to the brain, where the electrical impulses are interpreted as an image.

The cells within the retina that are directly responsible for the conversion of light to an electrical impulse are called photoreceptors. There are two types of photoreceptors: rods and cones. The rods are responsible for dim light vision, and the cones are responsible for bright light and color vision. Progressive Retinal Atrophy begins with degeneration of the rod photoreceptors. This may be noticed by pet owners as night blindness or decreased “confidence” in dimly lit areas.

As the degeneration of rods progresses, the cones will begin to degenerate. Therefore, loss of vision in brightly lit environments will occur later in the progression of the disease. As PRA progresses slowly, many dogs will learn to partially accommodate for their visual deficits through their senses of hearing and smell. Because of this accommodation, it is not uncommon for some pet owners to notice the visual deficits only after significant degeneration of both rods and cones has occurred.