Progressive retinal atrophy, or PRA as it is frequently termed, is a long recognized, hereditary, blinding disorder. It is inherited as a simple autosomal recessive in most breeds. The first modern description of this problem was in Gordon Setters in Europe, in 1911, but since then PRA has been recognized in most purebred dogs. Millichamp et al. In 1988, described PRA in Tibetan Terriers. Also in 1988, it was found that PRA in Cockers, Poodles and Labradors was the result of a mutation at the same gene locus in all these breeds.

PRA is a disease of the retina. This tissue, located inside the back of the eye, contains specialized cells called photoreceptors that absorb the light focused on them by the eye’s lens, and converts that light, through a series of chemical reactions into electrical nerve signals. The nerve signals from the retina are passed by the optic nerve to the brain where they are perceived as vision. The retinal photoreceptors are specialized into rods, for vision in dim light (night vision), and cones for vision in bright light (day and color vision). PRA usually affects the rods initially, and then cones in later stages of the disease. In human families, the diseases equivalent to PRA (in dogs) are termed retinitis pigmentosa.

In all canine breeds PRA has certain common features. Early in the disease, affected dogs are nightblind, lacking the ability to adjust their vision to dim light; later their daytime vision also fails. As their vision deteriorates, affected dogs will adapt to their handicap as long as their environment remains constant, and they are not faced with situations requiring excellent vision. At the same time the pupils of their eyes become increasingly dilated, in a vain attempt to gather more light, causing a noticeable "shine" to their eyes; and the lens of their eyes may become cloudy, or opaque, resulting in a cataract.

The big difference in PRA among breeds is in the age of onset and the rate of progression of the disease. Certain breeds, notably including the Collie, the Irish Setter, the Norwegian Elkhound and the Miniature Schnauzer, have early onset forms. In these breeds the disease results from abnormal or arrested development of the photoreceptors—the visual cells in their retina, and affects pups very early in life. In other breeds, including the Miniature Poodle, the English and American Cocker Spaniel, and the Labrador Retriever, and many other breeds, including the Tibetan Terrier, Tibetan Spaniel, and Lhasa Apso, PRA is much later in onset. Affected dogs in these breeds appear normal when young, but develop PRA as adults.

Diagnosis of PRA is normally made by ophthalmoscopic examination. This is undertaken using an instrument called an indirect ophthalmoscope, and requires dilatation of the dog’s pupil by application of eyedrops. Broadly speaking, all forms of PRA have the same sequence of ophthalmoscopic changes: increased reflectivity (shininess) of the fundus (the inside of the back of the eye, overlain by the retina); reduction in the diameter and branching pattern of the retina’s blood vessels; and shrinking of the optic nerve head (the nerve connecting the retina to the brain). These changes occur in all forms of PRA, but at different times in the different breed-specific forms. Usually by the time the affected dog has these changes there is already significant evidence of loss of vision.

Optigen Testing (by Diana Stevens),
Wylanbriar Labradors
 

The BVA/KC eye testing scheme has been around for about 25 years or so now. It has been tweaked and fine tuned and moved about but the general idea of it has remained the same. That if a dog is examined by an expert for the eye conditions which are common to Labradors, and is clear (or 'unaffected' as it is sometimes described) then one can mate in safety to another dog, also carrying a current clear eye certificate and know you are doing the best possible by the puppies produced for future good eye health.
However eyebrows were raised when two dogs with clear eye certificates were mated, a puppy from that was tested at 2, 3 or more years of age, and FAILED his own eye certificate. How can that be? Well, the answer is simple and that is that both his parents although clear themselves were genetically CARRIERS of the eye problem he failed on and so, when put, perfectly ethically together, were always going to produce a proportion of pups affected with the most nasty of all eye problems, Late Onset PRA or GPRA as it is better known.
So work was started on a DNA test which would show not only if the parents were affected or unaffected with GPRA but ALSO, importantly, the result the paper BVA/KC eye test itself couldn't see, if they were Carriers.
After many years of waiting we finally have a test, run by the company 'Optigen' in the United States, to exactly as above, give the GENETIC eye status of any dog before breeding from it.
Results will return as your dog being either: Clear, Carrier or Affected.
This test is not to rule any dog out of the gene pool, but to give us a clearer idea of the playing field and to be able to make breeding decisions accordingly.
The various breeding combinations using Optigen results are:

Optigen Status of Parents Outcome for Pups Clear x Clear = 100% Clear offspring Clear x Carrier = 50% Clear 50% Carrier offspring Carrier x Carrier = 25% Clear 25% Affected 50% Carrier Offspring Clear x Affected 100% Carrier offspring



So you can see that when Optigen tested, even an AFFECTED dog could be mated to a clear dog and never produce a single puppy who will be affected by GPRA.
Indeed because you can Optigen test from a very young age, literally from 6/7 weeks of age, if you undertake a Carrier x Clear mating, and don't wish to keep a Carrier puppy, you can Optigen test the best two or three pups (at a reduced rate for this what is called 'litter testing') and keep only a clear puppy. The Carrier pups will never develop the problem, of that you can be CERTAIN, and so can be sold as pets comfortably.
Testing is by way of a blood test at your vets, and booking a test online at the Optigen website -
 www.optigen.com . Sending the blood from your vets to Optigen by way of airmail post and paying for the test by credit card when booking. It is not complicated and not daunting. It also costs around £100-£150 per dog to test and this is done only once in a dogs life. A small drop in the ocean for the 'value' of the results to that breeder and the gene pool as a whole.
You hear SO many reasons for not Optigen testing. The main reason really being that breeders are scared of what could be the result. Years and years of clear eye certificates or worse still simply an opinion that they have had 'no eye problems' can lull breeders into a false sense of security.
There has been around a 35% return on Optigen tests finding that dogs tested from the UK are in fact Carriers. This is a high percentage. I am entirely practical that the majority testing are those who consider there *might just* be a problem so therefore are being proved right. But many lines where people didn't for a second think there was any problem there are finding, in fact there are.
There are no clear LINES only individual clear dogs. And they are only proven as clear if they are Optigen tested. A dog can clear (like one of my own several years ago) 7, 8, even 9 eye certificates in his life and sire hundreds of puppies without anyone realising he is a Carrier. Then just one Carrier bitch mated with him can mean several young dogs from that litter devastating their families by going blind at a very young age.
"Where does health testing end?" Some breeders will counter.... "You need to breed for the WHOLE Labrador NOT just eyes". And I agree, but with such a simple and reasonably priced test available to give a 100% genetic certainty, not just a 'stab in the dark' result that really in the scheme of things hip and elbow scoring do in comparison, the puppies produced by us and the owners that buy them deserve it.