What is PRA?
This is a retinal abnormality that occurs in many breeds and leads to blindness. There are two types of light-sensitive cells in the retina, namely the rods and the cones. The sticks are mainly used to see in low light (in the evening). The cones are mainly used for seeing in lots of light (during the day) and for colouring.
The dog has for the most part rods. The rods and cones are not evenly distributed over the retina. In the central area, close to the papilla (blind spot), the majority of cones are still relatively large. Peripherally, on the edge of the retina, there are almost exclusively rods. If the stick or cones are deviated from before birth, they are called dysplasia. Degenerate (decayed) in later life, we speak of atrophy.
The normal image of the retinal vascular membrane. The central white-pink spot is the entering optic nerve (blind spot); from there the retinal blood vessels run to the periphery. Only the vessels of the retina are visible. The green area is the reflector layer of the choroid membrane behind the retina.
If the cones are affected first, then this is preceded by Pigment Epithelial Dystrophy (PED). If the rods are affected first, then night blindness (old name: generalised PRA) will occur first.
- Pigment epithelial dystrophy or PED (old name: day, tunnel or central PRA (CPRA))
- Night blindness (old name: generalised or peripheral PRA)
PED is characterized by the occurrence of pigment accumulations in the pigment epithelium of the retina. In a more advanced stage of the disease, the cones degenerate. As a result, the dogs will see less well during the day. Eventually, the rods are usually also affected and most dogs become completely blind between the ages of 5 and 9. However, PED is rare.
By far the most important form of PRA is the form of night blindness; this can be divided into at least five types, but for the breeder or owner it is most important to distinguish two groups:
- Blindness that increases rapidly and occurs at a young age. This is because the rods and possibly also the cones are immediately wrongly laid (= dysplasia), followed by degeneration (= atrophy). The night blindness then occurs from an age of 8 to 12 weeks.
- Slowly increasing and at the age of 5-10 years blindness occurs. The rods and cones are normally laid, followed by a fairly rapid atrophy. This form occurs in the Dwarf Poodle, American and English Cocker Spaniel and many other dog breeds, of which it is not yet precisely known which cells are or become abnormal (for this purpose test pairings and eye sections are necessary). The night blindness starts in these animals at the age of 2-5 years. The animals eventually become completely blind at the age of 5-10 years.
What can be done about it?
There is no known therapy to prevent, stop or cure the process.