At the moment all we can:

• Routinely examine all breeding stock and offspring for those problems that DNA testing doesn’t uncover –eg cataract.
• Test mating is no longer needed because of the availability of the DNA test.
• A national recording scheme of all pedigree stock is essential in order that the disease be eradicated in some of the worst affected breeds.
• Cataract development may follow in the latter stages of the retinal disease. The development of cataract will of course further impede the affected animal’s vision, but of course cataract surgery is not going to give any real benefit to the animal unless it is obvious that the onset of cataract produces a sudden change in vision and blindness. Surgery in selected cases can be of benefit and allow some use of the remaining retinal function but remember the retina is gradually degenerating.
• With the development of cataract it is possible that an inflammatory reaction may occur within the eye due to material leaking out of the lens into the eye. The eye reacts against this foreign protein. If this occurs the eye may show signs of redness and there will be some discomfort to your pet. Eye drops should be given for this and may involve long term treatment to control the problem. No treatment can result in continuing pain and the possibility of glaucoma developing in the eye.

• There is no known treatment for this problem as yet with total blindness the end result. The rate of progression can be different from one individual to another with the development of cataract variable as well.

There are other disease conditions which affect both cats and dogs where the final stages of the retinal disease can mimic the appearance of Generalised PRA (so called pheno-copies). It is very important from a breeder’s viewpoint that some distinction is made between the genetic and the non-genetic causes of vision loss in an animal. With this in mind it is most important before one hangs the label of blindness caused by a genetic disease i.e. Generalised PRA on an animal, that one consider the history, the breed, the age of onset of the disease and factors such as the appearance of the retinal disease (e.g. it is unlikely to be a genetic disease if only one eye is affected or there is an obvious difference between the two eyes).

Any disease which causes blindness in an animal is distressing probably more to the owner than to the animal. One of the advantages of Generalised PRA is that the onset of blindness is gradual thus giving the animal time to accommodate to its disability and better utilize its other senses such as hearing and smelling. Completely blind animals can have an excellent quality of life and one should not consider, unless in extreme situations, euthanasia.

New Zealand breed clubs are working to eliminate genetic disease from those breeds at risk. This involves yearly testing of pedigree animals and the interchange of information between breed members of the genetic status on dogs being used as studs (although this certainly could be improved further). The development of a national eye scheme is underway with the possible collation of all eye certificate examination results being logged into a national database.

Craig Irving
EYEVET SERVICES
Craig Irving – Registered Specialist Veterinary Ophthalmologist
84 Pitt Street
Palmerston North Ph 06-3575887 Fax 06-3575863
craigeyevet@clear.net.nz

DNA test providers for Inherited Canine diseases

• Genetic Science Services- Australia-www.geneticscienceservices.com
• America- www.optigen.com
• Both these sites offer a range of DNA tests for ophthalmic problems in dogs as well as other inherited diseases.