Chris HewisonHewison's Corner

More about eyes

You may recall that last year I wrote an article describing goniodygenesis and glaucoma in flatcoated retrievers. Glaucoma is in Schedule A of the KC/BVA Eye Test Scheme, this means the disease is 'Certified' and we should all screen our dogs for this disease (please read my earlier article).

Since then I have been asked by many people about other eye diseases, especially about PRA, as this will soon be added to Schedule B - 'Under Investigation' in flatcoated retrievers under the scheme.

Generalised Progressive Retinal Atrophy (GPRA)

Consider the eye is a globe, the bit we see lets the light in, the bit at the back (the retina) converts this light into electrical signals that go down the optic nerve to the brain. The retina is made up of cells called photo-receptors (you may know of these as 'rods' and 'cones'). GPRA describes a range of different diseases where these cells either fail to develop early in life (dysplasia) or when they degenerate prematurely.

The first sign of GPRA is usually poor vision at night, this progresses at a varying speed to complete blindness. The age of onset varies from one case to the next and depends on the underlying disease process. The worst thing about this disease is that there is no cure and the affected dog will become totally blind.

Testing

To diagnose the disease a vet will use an ophthalmoscope to study the retina having first used drops to dilate the pupil. In GPRA the retinal blood vessels become narrower and the reflection of light from the back of the eyes gets brighter. As the disease progresses the vet may see a secondary cataract form in the lens.

Fortunately, since geneticists have completed mapping the DNA of the dog, it is becoming easier to screen certain breeds for the disease by taking mouth swabs or blood samples. This is proving an invaluble breeding tool where the gene mutation responsible has been identified. As the disease is still under investigation in flatcoated retrievers we cannot use this test for our dogs yet.

The following is taken from the advice currently issued by the Flatcoated Retriever Society Health Committee:

All stock should be examined on a regular basis for PRA; all popular stud dogs annually, all brood bitches at least every two years, and all stock definitely before breeding. This examination should be carried out well into old age, 8 years plus, as PRA can be of late onset.

The Health Committee's advice also extends to hereditary cataract and goniodysgenisis and can be reviewed at:

http://www.flatcoated-retriever-society.org/images/stories/health/eyes09.pdf