Progressive retinal atrophy

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Progressive retinal atrophy (PRA) is a genetic disease of the retina that occurs bilaterally and is seen in certain breeds of dogs. It causes progressive vision loss culminating in blindness. PRA is actually a group of retinal degenerations with different causes. Nearly all are hereditary. There is no treatment.

Diagnosis

Progressive vision loss in any dog in the absence of glaucoma or cataracts can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia. Other symptoms include dilated pupils and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, a darkened optic disc, and increased reflection from the tapetum due to thinning of the retina. Secondary cataract formation in the posterior portion of the lens can occur late in the disease. In these cases diagnosis of PRA may require electroretinography (ERG).

Types of PRA

Generalized PRA is the most common type and causes atrophy of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).

Generalized PRA can be divided into either dysplastic disease, where the cells develop abnormally, and degenerative, where the cells develop normally but then undergo a damaging change. PRA can be further divided into affecting either rod or cone cells. Rod cells detect shape and motion, and function in dim light. Cone cells detect color and definition, and function in bright light.

Generalized PRA

Commonly affected breeds:

• Akita - Symptoms at one to three years old and blindness at three to five years old.
• Miniature longhaired Dachshund - Symptoms at six months old.
• Papillon - Slowly progressive with blindness at seven to eight years old.
• Tibetan Spaniel - Symptoms at three to five years old.
• Tibetan Terrier - Symptoms at less than one year old, often blind by two years old, and cataract formation by four years old.
• Samoyed - Symptoms by three to five years old.

Rod-cone dysplasia type 1

• Irish Setter - Rod cell response is nearly absent. Night blindness by six to eight weeks old, often blind by one year old.

Rod-cone dysplasia type 2

• Collie - Rod cell response is nearly absent. Night blindness by six weeks old, blind by one to two years old.

Rod dysplasia

• Norwegian Elkhound - Rod cell response is nearly absent. Night blindeness by six months old, blind by three to five years old. This has been bred out of this dog.

Early retinal degeneration

• Norwegian Elkhound - Night blindness by six weeks old, blind by twelve to eighteen months old.

Photoreceptor dysplasia

This is caused by an abnormal development of both rod and cone cells. Dogs are initially night blind and then progress to day blindness.

• Miniature Schnauzer - Slowly progressive, not seen until two to five years old.
• Belgian Shepherd Dog - Complete blindness by eight weeks old.

Cone degeneration

• Alaskan Malamute - Temporary loss of vision in daylight at eight to ten weeks old. There is a purely rod cell retina by four years old.

Progressive rod-cone degeneration (PRCD)

This is a disease that starts in the rod cells and progresses to the cones.

• Poodle - Night blindness by three to five years old, blind by five to seven years old.
• English Cocker Spaniel - Occurs late in life, usually at four to eight years old.
• American Cocker Spaniel - Night blindness by three to five years old, blind one to two years later.
• Labrador Retriever - Night blindness by four to six years old, blind at six to eight years old.
• Portuguese Water Dog

Hereditary retinal degeneration

• Siberian Husky - Condition is linked to the X chromosome. Night blindness by two to four years old.

Central progressive retinal atrophy (CPRA)

CPRA is also known as retinal pigment epithelial dystrophy (RPED). It is characterized by accumulation of pigment spots in the retina surrounded by retinal atrophy. It is an inherited condition. CPRA occurs in older dogs. Peripheral vision is retained for a long time. Vision is better in low light and better for moving or distant objects. Not all affected dogs go blind. Secondary cataracts are common.

Commonly affected breeds

• Labrador Retriever
• Golden Retriever
• Border Collie
• Collie
• Shetland Sheepdog
• English Cocker Spaniel
• English Springer Spaniel
• Chesapeake Bay Retriever
• Cavalier King Charles Spaniel
• Briard - has an especially high frequency.

Hereditary retinal dysplasia

There is another retinal disease in Briards known as hereditary retinal dysplasia. These dogs are night blind from birth, and day vision varies. Puppies affected often have nystagmus. It is also known as lipid retinopathy.

See also

• Sudden acquired retinal degeneration

References

External links

• [Progressive retinal atrophy in Cavalier King Charles Spaniels]

 

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