Progressive Retinal Atrophy (PRA) is an inherited condition that many dog breeds are predisposed to. It is characterised by bilateral degeneration of the retina, resulting in progressive vision loss and eventual blindness. Secondary cataract formation is also commonly seen in the late stages of the disease but removal of the cataracts is unlikely to restore sight as the underlying retinal degeneration is usually too advanced already.
To date, PRA in the dog is not a disease that can be cured and affected patients sadly have to adjust to blindness. In the Tibetan Spaniel, PRA is a late-onset condition which may not be showing clinical signs before the age of 6 or 7 years. However, an eye specialist may detect clinical signs during an ocular examination as early as from 3 years of age.
PRA is caused by a genetic defect – but multiple different forms of the genetic mutation exist between different breeds or even within the same breed. The geneticists at the Animal Health Trust have named a mutation causing PRA in the Tibetan Spaniel PRA3 to distinguish it from other mutations causing the disease. During their investigations, they found that approximately two thirds of the clinical cases identified with PRA in Tibetan Spaniels to be carrying the PRA3 mutation – which means, that one third of cases of PRA in the Tibetan Spaniel are caused by other conditions or genetic mutations that have not yet been identified.
A DNA test is available for PRA3. Sampling for the test is easy and stress-free for the dog as it only involves a simple mouth swab. The swab kit is requested from the Animal Health Trust.
However, the DNA test should not replace the eye examination – and both should be used in synergy because:
- As explained above, genetic testing can only pick up approximately two thirds of dogs affected with PRA as one third of cases do not carry the PRA3 mutation. These dogs can only be identified on an ocular examination – and early detection of affected dogs is imperative to prevent these individuals to be bred from, keeping in mind that clinical signs of PRA may not be apparent to owners until well after the ‘breeding-age’ of the dog.
- Furthermore, a DNA test will only identify one very specific genetic mutation (one single eye disease) whilst an eye examination screens for a whole range of potentially inherited ocular conditions. The early detection of ocular abnormalities plays an important part in the surveillance of a breed for emerging inherited conditions. This is especially important in numerically small breeds – where there is a large shared gene pool and where an inherited condition could be widely disseminated into the breed before attention to its existence is drawn by clinical cases identified by owners and veterinary surgeons.
- Finally, an eye examination under the BVA/KC/ISDS scheme also provides an expert health check for your dog’s eyes and can yield information about other, non-inherited, diseases of importance.
If your eye specialist is concerned, he or she will refer you back to your own veterinary surgeon to arrange an appropriate treatment.