Progressive retinal atrophy
Progressive retinal atrophy (PRA) is an inherited eye disease that leads to blindness in dogs. PRA is a non-painful condition that tends to progress slowly over time, often starting with a decreased ability to see well at night.
While there is no cure available right now, most dogs adapt well to their vision loss and continue to have a good quality of life.
Several different genetic variants can cause PRA, but all of them lead to the same outcome: cell degeneration in the retina, which is located in the back of the eye.
There are two types of cells in the retina: rods and cones. Rods assist with night vision and motion detection, whereas cones help with day vision and color detection.
Dogs with degenerative PRA are born with normal rods and cones, but the cells start to break down sometime during adulthood. This slowly progresses into blindness, but the progression and age at which the majority of vision is lost will vary depending on the breed and the individual.
In true PRA, rods will die before cones, causing night vision to be affected first. When cones degenerate first, the condition is called achromatopsia, or day blindness.
A less common form of retinal disease occurs in puppies who are born with rods or cones that never develop properly, which leads to blindness much more quickly. These conditions are referred to as retinal dysplasia rather than retinal degeneration, but may still be called PRAs at times. Eventually, all genetic variations of PRA progress to complete blindness.
The breeds known to have genetic variants that put them at a higher risk for PRA, include, but are not limited to the following:
English and American Cocker Spaniels
Australian Cattle Dogs
Tibetan Terriers and Spaniels
Cardigan Welsh Corgis
These signs may not be apparent until later in the disease, as dogs will naturally acclimate to their vision loss. Signs may be more noticeable at night or when the dog is in a new environment.
Clinical signs may include the following:
Abnormally reflective eyes when a light shines on them
Reluctance to enter a dark room or go outside at night
Hesitance to go down stairs
Bumping into door frames or clumsiness in new surroundings
Cataract formation in both eyes
PRA is diagnosed with an eye exam focusing on the retina. Both eyes are equally affected by PRA, and dogs may also develop cataracts in the late stages of the disease.
Your veterinarian may refer you to a veterinary eye specialist to confirm a diagnosis with additional testing, such as electroretinography (ERG), especially if cataracts block the retinas from view.
It is important to differentiate PRA from other forms of blindness in dogs, since other diseases may cause pain or additional systemic side effects.
PRA management focuses on helping dogs avoid injury and feel safe in their environment as their vision declines. Steps to take include:
Adding supplemental lighting inside and outside the house — this may help in the early stages when only night vision is affected
Keeping furniture in the same arrangement
Using safety gates to block access to stairs
Guiding them with a leash when in unknown areas
Training with verbal commands (prior to vision loss)
Gene therapy is a prospective treatment for some specific types of canine PRA, but at this time, it has only been used in research settings, and it is not widely available. While there are no approved treatments for PRA, specific antioxidant supplements may improve retinal function and help to delay the formation of cataracts.
Unfortunately, nearly all dogs with PRA will eventually go completely blind. Dogs tend to acclimate well to vision loss, since most cases of PRA progress slowly, and affected dogs can go on to live otherwise healthy lives.
DNA testing is available for all known variants, but researchers have not yet discovered all the variants that cause PRA. The existing tests can detect if a dog is at risk of developing PRA, or if they are merely a carrier of a variant but not at risk of developing the disease.
One of the most common forms of inherited PRA is called progressive rod-cone degeneration (PRCD). Since this condition is recessive, two copies of the variant must be present to consider a dog at-risk. Dogs with two copies of the PRCD variant will almost always develop vision loss as an adult.
There are also a few known variants that are called dominant variants (requiring only one copy) or X-linked variants (requiring one copy for males and two copies for females).
However, some forms of PRA do not have any known genetic variants — meaning that a dog could still develop the disease even if they test negative for the known variants.
Dogs with PRA and dogs that test positive for known PRA variants should not be used for breeding without prior genetic testing and careful consideration of mate selection.