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 & 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 a dog sees.
Rods are responsible for vision in dim light i.e. night vision & peripheral vision
Cones are responsible for vision in bright light i.e. daytime & colour vision
With PRA disease, the retina wastes away (due to degeneration of cells) & 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:
- prcd-PRA (also known as Generalised PRA) where the entire retina is affected and
- Retinal Pigment Epithelial Dystrophy - RPED (also known as Central PRA) 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 (prcd-PRA)
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 RPED (CPRA)
With RPED the clinical signs show light brown pigment foci (lipofuscin) developing across the tapetal fundus. The pigment patches migrate & 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.
RPED 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 RPED is influenced by dietary deficiencies namely Vitamin E. He says that "research indicates that RPED results from an inadequate nutritional balance of Vitamin E. With better feed composition (good quality commercial dog food); especially with supplementation of vitamin E, RPED has essentially disappeared in most if not all breeds. The incidence of RPED was approx. 17% affected and now the incidence is almost 0%."
RPED 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 research, 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 a hereditary eye disease caused by a recessive gene. This means that an affected dog has either carrier or affected parents. 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. For more information on GPRA visit our PRA page.
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 (& 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.)
