Progressive Retinal Atrophy (PRA)

Progressive retinal atrophy refers to a group of inherited degenerative eye disorders, which lead to loss of vision. PRA affects both eyes simultaneously and is not painful

Blind Labrador Retriever
Original image by user Jo & Joey on Flickr. CC BY-NC 2.0.

Basic Facts

Name: Progressive Retinal Atrophy (PRA)

Hereditary: Yes

Description

Progressive retinal atrophy (PRA), is also referred to as progressive rod and cone degeneration (PRCD). The retina is a thin layer of nerves that lines the back of the eyeball. The purpose of the retina is to receive light and then change it into messages (neural signals), which are then sent to the brain to “read”. Think of the eye as a camera; the retina would be the film. The retina is a very important part of the eye. If the film in a camera is bad, there are no quality pictures.

The retina has two type of sensory cells that respond to light (photoreceptors); the rods and the cones. The rods work at low levels of light (night vision) and detect motion. The cones are responsible for color perception and details. Dogs have more rod cells than humans but fewer cones cells. That is why dogs see better at night than people, are more aware of movement, but have inferior color vision. In progressive retinal atrophy disorders, the rod cells are designed to die off.

Types of Progressive Retinal Atrophy in Dogs


PRA can affect certain dog breeds and mixed breeds.

Generalized PRA


Generalized PRA is the most common type of progressive retinal atrophy. It causes all the retina structures to waste away (atrophy). Commonly affected breeds are:
  • Akita
  • Miniature longhaired Dachshund
  • Papillion
  • Tibetan Spaniel
  • Tibetan Terrier
  • Samoyed

Progressive Red-Cone Degeneration (PRCD)


PRCD has a late onset, most affected dogs do not show signs of vision loss until 3 to 5 years of age. The rod cells are affected first, therefore dogs will initially have night blindness. Commonly affected breeds:
  • Australian Shepherd
  • Poodle
  • English Cocker Spaniel
  • Labrador Retriever
  • Golden Retriever
  • American hairless terrier

Central Progressive Retinal Atrophy (CPRA)


CPRA is also referred to as retinal pigment epithelial dystrophy (RPED). CPRA usually occurs in older dogs. The dog’s peripheral vision is kept for a long time. Not all dogs with CPRA go blind. Breeds affected are:
  • Beagle
  • Labrador Retriever
  • Golden Retriever
  • Border Collie
  • English Cocker Spaniel
  • Collie
  • Chesapeake Bay Retriever
  • Cavalier King Charles Spaniard
  • Briard

Dominant PRA


Dominant PRA affects English Mastiffs and Bull Mastiffs.  Usually affected dogs do not show symptoms of the disease until 2-3 years of age.

X-Linked PRA


The first symptoms usually appear at 6 months of age. X-linked PRA (inherited by the X chromosome) affects male Siberian Husky and the Samoyed breeds.

Symptoms of Progressive Retinal Atrophy in Dogs


Symptoms may include:
  • Night blindness
  • Pupils respond slower to light
  • Cloudy or opaque eye surface
  • Bumping into furniture or walls
  • Reluctance to use stairs
  • Miscalculates and stumbles, trying to get on or off furniture.

Causes of Progressive Retinal Atrophy in Dogs


Progressive retinal atrophy disorders are inherited. Most PRA disorders are passed down from the dam (mother) and sire (father) to their litter. Both the male and female must have the abnormal gene for the litter to have a PRA disorder; this is called an autosomal recessive disorder. If only one parent has the abnormal gene, the litter will not develop the disorder but will be carriers of the PRA gene.

A few PRA disorders are passed in a dominant inheritance pattern, which means the disorder can be inherited by the abnormal gene of only one parent.

Diagnoses of Progressive Retinal Atrophy in Dogs


If a dog is showing symptoms of progressive retinal atrophy he should be seen by a veterinary ophthalmologist. The ophthalmologist will exam the dog’s eye with an optical instrument (ophthalmoscope). If he suspects PRA he will perform a electroretinogram (ERG). The procedure is not painful and most dogs do not need to be sedated. This diagnostic test measures the response of the retina to light. The results of ECR can confirm progressive retinal atrophy in dogs.

Treatment of Progressive Retinal Atrophy in Dogs


There is no cure available for progressive retinal atrophy. The veterinarian may recommend daily antioxidant supplementation and vitamins, which may help slow down the progression of PRA.

Prognoses of Progressive Retinal Atrophy in Dogs


With time dogs that become blind from progressive retinal atrophy learn to adapt to their environment. The dog learns to depend more on his other keen senses. Blindness in dogs usually upsets the owner more so than the dog. Dogs that are blind can lead happy and fulfilling lives. There are a few online support groups for owners of blind dogs such as: www.blinddogsupport.com , www.blinddogs.net and www.blinddogrescue.org/dog-blindness/tips-for-owners/. These sites may be helpful in providing support and suggestions.

Prevention of Progressive Retinal Atrophy in Dogs


There are DNA blood tests available, which can determine if a dog is affected with PRA or is a carrier for PRA. Dogs that have PRA or are carriers of PRA should not be used for breeding. Not breeding dogs with progressive retinal atrophy can help prevent the disorder. Dogs that test positive for PRA should be spayed or neutered.