Progressive Retinal Atrophy (PRA)

PRA (Progressive Retinal Atrophy) is an inherited eye disease found in many breeds of dogs with varying ages of onset (the age when symptoms are noted and the dog starts to have trouble seeing). The commonest form of the disease in cocker spaniels is GPRA (Generalised Progressive Retinal Atrophy) which is also referred to as prcd-PRA.

How do dogs see?

They way in which a dog sees (it is the same for humans) is that light passes through the lens (of the eye) and is directed onto the retina, which contains specialised photoreceptor (light-sensitive) cells called rods and cones. These cells convert the light into electrical nerve signals, which pass along the optic nerve to the brain, where they are "translated" into images i.e. what we see.

Rods are responsible for vision in dim light i.e. night vision

Cones are responsible for vision in bright light i.e. daytime and colour vision

With PRA the retina becomes damaged and the rods and cones diminish and therefore they are unable to transmit the nerve signals to the optic nerve and therefore the dog is unable to see.

Definition of PRA

Progressive - a slowly developing disease process

Retinal - of the retina - the light-sensitive area at the back of the eye

Atrophy - degeneration (wasting away) and deterioration of the specialised light-sensitive cells in the retina

There are two forms of PRA found in cocker spaniels.

1. General PRA (also known as prcd-PRA) where the entire retina is affected and
2. CPRA (also known as Retinal pigment epithelial dystrophy) where only the central vision of a dog is affected (and therefore the dog doesn't become blind even though there is some loss of accurate eyesight).

Information about GPRA

GPRA is the most common form of PRA found in cocker spaniels. With GPRA, loss of night vision occurs initially and then day vision gradually deteriorates eventually resulting in total blindness. Opthalmoscopically progressive hyperreflectivity (due to retinal thinning) develops over the entire tapetal area. There is also gradual attenuation of the superficial retinal vasculature, the non-tapetal fundus develops a patchy distribution of pigment, and the optic disc atrophies.

Information about CPRA

With CPRA the clinical signs show light brown pigment foci (lipofuscin) developing across the tapetal fundus. The pigment patches migrate and may coalesce during the course of the disease and retinal thinning may be demonstrated by tapetal hyperreflectivity. Affected dogs are described as having reduced central vision. Peripheral vision is preserved. Affected dogs have poorer vision in bright sunlight but do not normally go completely blind.

CPRA is quite rare; in fact, it is almost unheard of. Our local eye vet, Paul Evans, MA, VetMB, Cert V Ophthal, MRCVS who runs the Eye Veterinary Clinic (a specialist Ophthalmology Referral Practice) tells me that CPRA is influenced by dietary deficiencies namely Vitamin E. He says that "research indicates that CPRA results from an inadequate nutritional balance of Vitamin E. With better feed composition (good quality commercial dog food); especially with supplementation of vitamin E, CPRA has essentially disappeared in most if not all breeds. The incidence of CPRA was approx. 17% affected and now the incidence is almost 0%."

CPRA testing is still performed routinely as part of the KC/BVA Eye test, however it is now a disease that is rare and whilst it is still worth monitoring it is not something that, based on reasearch, need overly worry breeders/owners.

GPRA - The Disease

In Cockers, GPRA has a variable age of onset, from as early as 18 months to as late as 9 years. It is inherited as a simple Autosomal Recessive gene, meaning that a copy of the GPRA gene must be inherited from BOTH parents for the disease to occur in a dog.

Testing Schemes for GPRA

Currently there are two testing schemes for GPRA. The traditional testing of KC/BVA Eye Examination and the DNA test undertaken by OptiGen. The results of testing are listed on the Kennel Club website and a dog's Kennel Club Registration document.

It is important to note, that with cocker spaniels puppies are not eye screened. The earliest recommended age for a visual eye examination is 12 months.

What can the vet see when he examines the dogs eyes?

Our eye vet has a camera linked to his PC (I forget the name of the product!) which allows him to take images of the internal structure of the eye and save the images on the dogs records (for future reference). Here is an image taken using this camera showing a normal retina (a dog without PRA), the other image is a dog with PRA (not owned or bred by ourselves).

GPRA/CPRA can be detected by visual examination of the eye (by a qualified veterinary ophthalmologist - not normally a general practitioner vet i.e. your local vet) only when the disease is readily apparent. The KC/BVA Eye Test cannot and does not detect affected dogs (who have yet to show symptoms due to late onset) or dogs, which are carriers of the disease but not affected themselves.

If a dog has not been DNA tested the KC/BVA Eye Test MUST be repeated ANNUALLY. This is a progressive disease, the fact that a dog is certified unaffected by GPRA one year does not mean he/she will be certified unaffected the following year or indeed in subsequent years.

In the case of PRA, PRA is a recessive disease which means the "Carriers" will not be affected (become blind) and they will "pass" the KC/BVA Eye Test. However, "Carriers" will transmit the disease to their offspring. Whether their offspring is affected is determined by the genetic status of the other parent. For example if a "Carrier" is mated to a "Clear" partner, 50% of the litter will be "Carriers" and 50% will be "Clear" - there will be no affected puppies. However, if a breeder relies ONLY on the KC/BVA test they cannot be sure whether they are mating a "Carrier" to another "Carrier.” Two "Carriers" will produce affected offspring (dogs that will become blind due to PRA).

The detailed eye examination is performed by veterinary surgeons who are specially appointed panellists by the British Veterinary Association. The examination is designed to identify ALL the abnormalities within the eyeball and associated structures, including the eyelids (of which the dog has three, upper, lower and one called the nictitans or 'haw'). Additionally the size and positioning of the eyes is recorded. 'All abnormalities' covers known inherited, congenital, non-inherited and acquired problems, diseases and deviations from anatomic normality.

Pedigree dogs registered with the Kennel Club, and dogs registered with the International Sheep Dog Society are eligible under the scheme for KC/BVA eye testing. Dogs should be tested before being bred and the clinical eye test should be repeated annually (unless a dog has been DNA tested) as PRA is a progressive disease. This means that the disease gradually advances from not clinically visible to clearly visible over a period of months/years.

KC/BVA Certificate of Eye Examination

Full information about the scheme can be found on the British Veterinary Association website.

For Powerscourt eye test results please see our test results page.

PRA can also be detected by DNA analysis. DNA testing (using a blood sample) can be undertaken as soon as a puppy is old enough and big enough to have blood drawn. The test is able to detect whether a dog is affected (but perhaps symptom free at the time of testing), whether it is a carrier (will not ever be affected but is capable of passing the disease onto its offspring) or whether the dog is clear of the disease.

With recessive conditions like PRA, there are 3 genetic categories, "affected", "normal" (clear) and "carriers". Affected animals have two copies of the faulty PRA gene, one inherited from each parent. Carrier animals have one faulty copy of the PRA gene but appear perfectly healthy and cannot be distinguished from normal dogs by eye screening. Normal animals are entirely free of the faulty gene.

Unless breeders DNA test their breeding dogs (or know the genetic status via parentage) there is no way of identifying which category their breeding stock falls into unless the KC/BVA test identifies a dog as affected at the time of examination. The eye examination cannot determine whether the dog is a carrier or whether the dog will go on to develop the disease at some time in the future.

OptiGen prcd-PRA DNA Report / Old Style OptiGen 'Normal/Clear' Certificate

For more information about OptiGen testing for prcd-PRA please visit OptiGen's website. For more information about PRA please see here.

Please note, clinical eye examinations are NOT carried out on cocker puppies. The parents of the puppy should be examined. If any breeder of Cocker Spaniels tells you that the pups have been eye tested then you need to ask a few more questions!

When buying a puppy:

You should ensure that at least one parent (preferably BOTH parents) have been DNA tested for PRA and that at least one parent is "Normal/Clear.” If DNA testing hasn't been undertaken then at the bare minimum you should ensure that both parents of your puppy have current clear eye certificates showing that neither parent is affected by prcd-PRA at the time they were examined.

Another inherited eye disease found in cocker spaniels is Glaucoma. Glaucoma is the elevation of pressure inside the eye, known as intraocular pressure (IOP) beyond a specific point at which vision is compromised or is no longer possible. Glaucoma is a frequent cause of blindness in humans and animals.

The eye examination (called gonioscopy) for Glaucoma is only required once in a dogs life because it's not a progressive disease, the pre-disposition for this disease is either evident or not evident and can be detected the first time a dog is specifically examined for this disease. The examination for Glaucoma is a visual examination conducted by a qualified veterinary ophthalmologist.

Inheritance of Glaucoma depends entirely on the severity of goniodysgenesis in both parents - a slightly affected dog mated to a clear partner will not produce puppies affected with Glaucoma. Gonioscopy is not routinely performed as part of the KC/BVA eye test; this test must be requested separately (and needs to be performed prior to the standard KC/BVA test.) All Powerscourt cockers are routinely tested for Glaucoma at 12 months of age (this test needs to be done only once.)