What is PRA?

What is PRA ?
By Jenny Drastura

Reproduced with permission from The Lhasa Apso Reporter

Inherited retinal degenerations (generalized progressive retinal atrophy [PRA]) are a group of progressive retinal diseases that can be subdivided into photoreceptor degenerations, which begin after the retina matures, and photoreceptor dysplasias, which begin before the retina fully develops (less than 12 weeks).

Genetics: autosomal recessive in most breeds.

Prevalence: More prevalent in dogs than cats. Early onset PRA (3-4 months to 2 years) more common in Irish Setter, Collie, Norwegian Elkhound, Miniature Schnauzer, Belgian Shepherd. Late onset PRA (later than 4-6 years) more common in Miniature/Toy Poodle, American and English Cocker, Labrador Retriever, Tibetan Terrier, Miniature Longhaired Dachshund, Akita, Samoyed. Sudden Acquired Retinal Degeneration (SARD) occurs primarily in Brittany Spaniels, Miniature Schnauzers and Dachshunds.

Signs: A gradually progressing night blindness that ultimately affects vision in bright light. Owners may notice dilated pupils or brighter tapetal reflex at night. Many affected dogs develop cataracts. SARD dogs lose vision in 1-4 weeks, have increased thirst and urination, show increased hunger and may have slow or absent pupillary light reflexes. Affects both eyes symmetrically.

Causes: Genetic; retinal and optic nerve atrophy occur in animals with chronic or uncontrolled glaucoma. Retinal degeneration can occur secondary to scarring from previous multifocal or diffuse retinal detachment or inflammation. Severe deficiency of Vitamin E or A may cause partial or complete retinal degeneration in dogs and cats. SARD may be idiopathic.

Diagnosis: Opthalmic examination required to differentiate PRA from other conditions.

Treatment: The condition is irreversible, but painless. Most blind animals function very well. No effective medical treatment is known.

Prevention: Dogs suspected of having PRA and known carriers should not be bred.

Source: Tilley, Larry P., DVM, and Francis W.K. Smith Jr., DVM. The 5 Minute Veterinary Consult. Baltimore: Williams & Wilkins, 1997.