What are cataracts?
Cataracts are cloudy areas in the lens inside the eye which is normally clear. A normally clear lens allows light to pass through to the back of the eye so that the dog can see well-defined images. If a part of the lens becomes opaque light does not pass through easily and the dog's vision becomes blurry - like looking through cloudy water or a fogged up window. The more opaque (cloudier) the lens becomes, the worse the vision will be.
Cataracts can be hereditary or non-hereditary. Hereditary cataracts are the most common. Non-hereditary cataracts are usually linked with metabolic diseases, such as diabetes, and can also be associated with trauma. Cataracts are also commonly seen in older dogs due to the normal aging process and can eventually cause blindness. Our concern is for hereditary cataracts.
How are cataracts inherited?
The disorder shows an autosomal recessive mode of inheritance ie two copies of the defective gene (one inherited from each parent) have to be present for a dog to be affected by the disease. Individuals with one copy of the defective gene and one copy of the normal gene, called carriers, show no symptoms but can pass the defective gene onto their offspring. When two apparently healthy carriers are crossed, 25% (on average) of the offspring wil be affected by the disease, 25% will be clear and the remaining 50% will themselves be carriers.
Under most circumstances there will be a much greater number of carriers than affected animals in a population. Eventually it will be important to eliminate such carriers from the population since they represent a hidden reservoir of the disease that can produce affected dogs at any time.
In the diagram to the left you can see how easily an untested affected dog can wreek havoc in a population of one breed. At best an affected male or female will produce carriers and at worst, mated to another affected untested dog, will produce 100% probability of all puppies being affected.
So what does this have to do with bichons in the UK?
Bichons were placed on Schedule A of the BVA/KC eye testing scheme on 1 January 2012. In July 2012 it became mandatory for all Assured Breeders to test both sire and dam for hereditary cataracts (HC) to entitle them to register their litters under the Assured Breeders Scheme.
To date all dogs tests throughout 2012 and 2013 have been unaffected which is great news for the breed. However, this does not mean we should be complacent. One untested and affected bichon can wreek havoc in a population. By continued testing we are demonstrating a public commitment to health in our breed and embracing a prevention rather than a cure policy.
When buying a puppy you should ask a breeder to show you the eye testing certificate for both sire and dam.