The gene is recessive and only if a dog gets a gene from EACH parent, it will develop PRA.
A single-carrier will NOT develop PRA, but will pass on a gene to ½ of it's offspring, and an PRA affected dog will give a gene to each and one of it's offspring.

PRA in papillons are a late onset form. The first signs can usually been seen by ophthalmologic examination at the age of 3-4 years, but they often are overlooked because the initial stages are so very-very faint. The bloodvessels are thinning and deteriorating. Later on a mirror like reflex are seen from the retina. Sometimes the owner will notice the dog to have some reluctance against going out in a dark yard, climbing stairs or generally moving around strange places in the dusk. But very often there are nothing at all, which makes anyone suspect problems with the dog's sight.

Notice the different colorings of the eyes. The PRA-eyes are sort of opaque, bottomless, the flashlight are being reflected completely by the degenerated retina. The others are bright yellow to greenish, with no halo around. The pupils are well defined, and not as wide open as in the PRA-dog.
Some of the young dogs were really quite difficult to photograph, because their pupils had such a swift reaction so the colorings wasn't seen.
But the PRA-dog's eyes always turned out this way.

There have been diagnosed PRA in dogs bred in UK, USA, Norway, Holland, Iceland, Sweden and Denmark, but of course most PRA-cases are found in those countries, who thoroughly test their dogs.

In Denmark and Sweden the breeders can't get their puppies’ registered unless both parents have been tested clear of PRA within the last 12-month before mating. If a dog is diagnosed PRA, then it will be excluded from breeding as well as it's parents and offspring.

Back in '92 Pia Hansen, Gold Wings, started gathering eye-test-results. Hoping to map the gene in order to prevent breeding dogs who were carrying the gene.
Lene Kiilerich, Emira's, has now by great effort turned these data into a huge database containing over 30.000 papillons/phalenes - whereof over 3000 test-results.

Knowing about the genetics and the fact that we are dealing with a recessive gene looking for carriers in a pedigree in order to avoid them in ones breeding program makes very little sense.
Actually to only sensible way to minimize the incidence of PRA, is to make sure NOT to breed affected dogs......How??
One way is to wait breeding before the dog is at least 3½ or older, the longer you wait the lower the risk the dog will turn out affected.
A dog tested clear at 2 years of age might still have a 40% risk of being affected - cleared at 4 years the risk is down to 2%

The test methods today are normal opthalmoscopy and in very few countries ERG.
By the opthalmological method, the vetenarian looks through the dilated pupils and visually examines the retina using different kind of optical instruments.
The disadvantage of this method is that the early stages of PRA are very often not visible before the dog is 3-4 years. This is true in 70 % of the cases.
Specially trained veterinarians do this test.

By ERG the dog has to be anaesthetized. Then a special contact lens are placed on the eye, and the eye are exposed to various light sources: glimpses, red/blue and white. The eye/retina's responses to the light are recorded, and afterwards these records are evaluated, preferably against a set of normal papillon retina-curves. The diagnose is reliable at 95% at 2 year of age
Unfortunately this test is still very rare, highly costly and time consuming. It is only done at very few places in the world.

Papillon Club America is sponsoring this research.

In time only a single bloodtest is needed to determine whether a dog is genetically free, carrier or will develop PRA.

As mentioned in the ECS-story - what we think we know today, may not at all be the whole truth, but remember: We are part of the future made today...