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Progressiv retinal atrophy (PRA)
Progressive retinal atrophy is a group of genetic diseases seen in certain breeds of dogs. It is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness.
The term progressive retinal atrophy covers several types of inherited degeneration (deterioration) of the retina. There are two main classifications of the disease processes involved in PRA:
1. a primary effect on the photoreceptors (generalized PRA),
2. abnormalities of the pigment epithelium behind the photoreceptors which causes secondary photoreceptor degeneration (central PRA or, more recently, RPED).
Generalized PRA:
These diseases affect primarily the photoreceptor cells. Both eyes are similarly affected and dogs eventually become totally blind.
Early onset photoreceptor dysplasia:
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.
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.
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.
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.
Taken from: http://www.upei.ca/~cidd/Diseases/ocular%20disorders/Progressive%20Retinal%20Atrophy.htm