Primary lens luxation (PLL) testing for dogs

Primary lens luxation (PLL) is one of many canine health conditions that affect the eyes, and while it can occur as a complication of other eye disorders such as cataracts or glaucoma if left untreated, it is much more commonly found as a hereditary health condition that is passed on down the breed line from parent dogs to their offspring.

Primary lens luxation is widely spread across the gene pools of certain breeds and types of dog, and in order to limit the spread of the condition and prevent future generations being affected by the condition, The Kennel Club and the British Veterinary Association strongly advise that breeding stock from certain particularly at-risk breeds be tested for the markers of the condition before they are allowed to mate.

In this article, we will look at primary lens luxation testing for dogs, what it entails and what sort of dogs should be tested. Read on to learn more.

More about primary lens luxation

Primary lens luxation is a condition that affects the eye’s lens-the transparent part of the eye at the back of the pupil that lets light into the eye and focuses it at the back of the eyeball, where nerves transmit messages about what the dog is seeing to the dog’s brain. The lens itself is secured in the right place by very fine strands around its edges, which deliver blood and oxygen to the eye.

PLL causes the lens of the eye to float within the eye, rather than being secured where it should be by the strands that are designed to secure it in place. Understandably, this causes a range of problems, such as the risk of damage to the retina’s nerves, which can be painful and also lead to the potential for retinal detachment, or other issues such as glaucoma due to an increase in pressure in the eye.
Unlike certain other hereditary eye problems in dogs like progressive retinal atrophy, primary lens luxation can be very painful, as well as also potentially causing blindness.

What sort of dogs are prone to the condition?

Any dog can potentially develop primary lens luxation as a secondary complication of other eye problems like glaucoma or cataracts, but the primary means of transmission of the condition is by heredity, and dogs that are themselves affected by the hereditary form of the condition (rather than developing it due to another issue) run the risk of passing the condition on to their own offspring.

Some of the breeds of dog that are classed as being at particular risk of the condition include the Chinese crested, miniature bull terrier, and a significant number of other terrier breeds too. You can find out if the breed of dog that you own is considered to be at risk for the condition by using The Kennel Club’s Breed Information Centre Tool.

How does the heredity of primary lens luxation work?

Primary lens luxation is an autosomal recessive condition, which means that in order for a dog to be affected by the condition themselves, they must inherit two copies of the mutated gene that leads to the issue, one from each of their parent dogs.

Dogs that inherit just one copy will not suffer from the condition themselves, but will become a carrier for it, which again, increases the risk of it being passed on further within the breed line.

While advice for dog breeders on hereditary health conditions is usually that dogs shown to be affected by or a carrier of the condition in question should not breed, with primary lens luxation, the advice offered is rather different.

Due to the sheer number of dogs of certain breeds that are carries for the condition, removing all of these dogs from the breed’s gene pool in order to prevent PLL might actually cause more problems than it solves, in terms of leaving such a small range of genetically different dogs left that breeding only clear dogs is apt to lead to the development of other hereditary health conditions, due to a lack of genetic diversity remaining.

Because of this, dogs that are carriers for PLL (and in some cases, even affected dogs) may still be bred from, but it is really important that they be bred only with dogs that are clear (neither affected by nor carriers of) the mutation.

Knowing the status of dogs intended for breeding is therefore really important, which is why testing for PLL is in its turn important.

Testing for primary lens luxation in dogs

The test for primary lens luxation in dogs is a simple DNA test, which requires a sample such as blood or a buccal swab from the inside of the dog’s cheek-your vet can take the sample for you. The sample is then sent off to a laboratory for assessment to return your dog’s status. For a list of laboratories that can perform the test, check out the list on The Kennel Club website.