Papillon Rescue UK

What is progressive retinal atrophy?

The cells of the retina receive light stimuli from the external environment and transmit the information to the brain where it is interpreted to become vision. In progressive retinal atrophy (PRA), deterioration of the retinal cells causes blindness.

The retina lines the back of the eye. The inner layer is the neural retina (called simply the retina) which has 9 layers, the outermost of which consists of the photoreceptor cells - the rods and cones. The outer layer of the retina is the retinal pigmented epithelium (RPE). In dogs the retina is not mature until 6 or 7 weeks of age.

The term progressive retinal atrophy covers several types of inherited degeneration (deterioration) of the retina. Sub-classifications of PRA are based on the age at which dogs show signs of the disease and the type of retinal cell which is affected.
Generalized PRA: These diseases affect primarily the photoreceptor cells. Both eyes are similarly affected and dogs eventually become totally blind.

i) Early onset photoreceptor dysplasias: In these conditions, the photoreceptor cells develop abnormally in the first few weeks after birth, and then degenerate along with the inner layers of the retina.

ii) Later onset photoreceptor degeneration (progressive rod-cone degeneration): Here the retina matures  and functions apparently normally for varying periods of time before degenerating. Dogs are not usually clinically affected until 1 year of age or more, although abnormalities can be seen in the eye and on the electroretinogram (ERG) long before owners notice signs of visually impairment.

Progressive rod-cone degeneration has similarities to retinitis pigmentosa in people.

Central PRA:(also called RPE dystrophy) The abnormality is in the retinal pigmented epithelium (RPE). The photoreceptor cells will also degenerate eventually. The rate of vision loss is much slower than with generalized PRA, and not all dogs become totally blind.

One of the aims of Papillon Rescue UK is to help towards research into identifying the source of these diseases with the hope of an eventual cure.


What does progressive retinal atrophy mean to your dog & you?

Generalized PRA - early onset: The first sign is generally failing night vision, as early as 6 weeks of age, and this progresses to complete loss of vision by about 1 - 2 years of age. Collies may retain some vision until the age of 2 - 3 years.  In miniature schnauzers, poor night vision usually develops later (6 months to a year) and there is advanced loss of vision by 3 to 4 years. Affected Alaskan malamutes are day-blind (hemeralopia) at 8 to 10 weeks of age; night vision is never affected.

Generalized PRA (progressive rod-cone degeneration) - late onset: Generally night blindness is noticed between 2 and 5 years of age (depending on the breed) progressing to total blindness within a year or so. Peripheral vision is lost first.

Central PRA (CPRA)  - retinal pigment epithelial dystrophy (RPED): Loss of vision occurs much more slowly than in generalized PRA, without initial night blindness.  Affected dogs may not lose vision completely. Because the changes are in the centre of the retina, affected dogs initially have trouble locating still objects in bright light.

How is progressive retinal atrophy diagnosed?
There are no obvious external changes to the eyes. You may notice that your dog has difficulty getting around when the lights are turned off, or when outside at night. If you suspect that your dog has impaired vision, your veterinarian will look for abnormalities with an ophthalmoscope. PRA may also be detected by electroretinogram (ERG) before your dog has any apparent visual difficulties. Electroretinography, which measures electrical patterns in the retina, is usually only available in specialty veterinary centres.

Genetic testing is quickly becoming available for different forms of PRA in different breeds. The advantage of such testing is that it can identify dogs whose sight is unaffected, but who are carriers of the disorder (heterozygotes).

How is progressive retinal atrophy treated?
There is no treatment for PRA. The degree of visual impairment varies with the breed and specific type of retinal degeneration as described above, but most affected dogs will ultimately be completely blind. With their acute senses of smell and hearing, dogs can compensate very well, particularly in familiar surroundings, to the point where owners may be unaware of the extent of vision loss. You can help your dog by developing regular routes for exercise, maintaining consistent surroundings, introducing any necessary changes gradually, and being patient.

Breeding advice
Breeding is not advised for any dog with PRA, or for the parents (assumed to be carriers). Siblings should be carefully screened by electroretinogram if they are considered for breeding.  Generalized PRA can often be detected by electroretinography at least a year before clinical signs are apparent.