Progressive retinal Atrophy ( PRA3 ) is an inherited eye disease affecting Tibetan spaniel and Tibetan Terrier breed. PRA3 is a progressive disease with late onset of symptoms. The disease is characterised by degeneration of both rod and cone photoceptors. Degeneration of rod receptors leads to night blindness and loss of peripheral vision, whereas degeneration of cone photoreceptors results in loss of central vision and eventually complete blindness.
Most PRA cases in the Tibetan Spaniel (TS) are clinically indistinguishable from other forms of PRA. The mode of inheritance appears from pedigree information to be autosomal recessive and the age of diagnosis is relatively late, typically at approximately 5 years of age . No mutations have previously been associated with PRA in the breed.
Although the reported average age of clinical diagnosis in dogs affected with PRA3 is about 4.5-5 years of age, many breeders may delay screening their dogs until they notice obvious signs that their dog has visual problems, by which point the disease is often advanced. It is therefore possible, if not highly likely, that the age of onset of PRA3 is much earlier than the estimated 4.5-5 years.