Primary Lens Luxation or PLL is caused by a genetic defect in the zonular (eye) anatomy. This has been found to be an inherited condition in many terrier breeds such as Miniature Bull Terrier, Jack Russell Terrier and the Tibetan Terrier, it is also found in many other breeds.
In an affected the zonules start to break down during the dogs early life (usually 3 to 5 years) resulting in increased movement of the lens. Initially partial disinsertion occurs and eventually it luxates (dislocates) completely.
PLL does not show up until the dog is 3 to 5 years of age and in most cases breeders would have already bred with the dogs.
DNA testing (Bucal cheek swab) has revealed that puppies tested fall into three categories:
If a puppy acquires the mutated gene from BOTH parents they are GENETICALLY AFFECTED and very highly likely to develop PLL.
Puppies whose DNA test revealed one mutated gene and one normal gene are classified as CARRIERS. Currently the risk of a CARRIER developing PLL is between 2% and 20%.
Puppies whose DNA test reveals two normal genes (no mutated genes) are classified as CLEAR and highly unlikely to develop PLL.
Our pro-active stance in trying to eliminate this disease in our dogs, by selective breeding, also ensures our gene pool will not be affected by careless breeding. And remember breeding CLEAR to CLEAR cannot produce carriers and therefore the progeny are clear by parentage and do not require testing.
The results of DNA testing to date show that this disease is NOT isolated to any particular line or State. It will only be a matter of time before we have blind dogs if breeders fail to test their breeding stock.
This particular genetic disease is detrimental to our breed and at this time, with DNA testing, and selective breeding we can control it and ultimately eradicate it from our breed.