ARTA strongly recommends Breeders test for PLL (Primary Lens Luxation) before breeding.

Primary Lens Luxation is an eye problem well known in many Terrier breeds and other breeds. The lens is held in place in the eye by fibers known as zonules. If these zonules stretch or break, the lens can fall out of place, or luxate. When this happens it often requires immediate veterinary attention to remove the displaced lens and prevent painful secondary glaucoma, and sometimes loss of vision.

PLL is inherited as a simple recessive trait. This means that a dog needs 2 mutated, or “bad” copies of the gene to show the disease. With dogs that have tested AFFECTED, a small percentage of the dogs that test CARRIER are also at risk of developing PLL. Owners and breeders should be aware of this and understand the implications of the test results so that they can make well-informed decisions for the future of individual dogs, and the breed as a whole.

Dogs that test AFFECTED have 2 mutated copies of the gene. The vast majority of these dogs will luxate at 4-8yrs of age, the typical age of onset for PLL. There were a few dogs in the study group that tested as AFFECTED but did not luxate until after 8 yrs of age, and some dogs testing AFFECTED have died from other causes without luxating. About 10% of the dogs reported to be clinically affected with PLL had onset of symptoms after 8 yrs of age. Because of this, the test results will say “AFFECTED/HIGH RISK”.

Dogs testing CARRIER are at a slight risk of developing PLL. Carriers have one normal and one mutated copy of the gene. They could pass either the normal copy or the mutated copy on to their offspring. Because there were very few cases of dogs in the research groups testing CARRIER who did appear to have PLL, the test results will say “CARRIER/LOW RISK”.

A dog testing NORMAL has 2 normal copies of the gene, is not at risk for developing PLL, and can only pass a normal copy of the gene to any offspring.

Credits: University of Missouri, College of Veterinary Medicine, Project Coordinator Liz Hansen

Below are links to explain what PLL is, and how it's treated. Prior to October 2009 there was NO test, and no way of knowing other than anecdotal evidence whether the issue was in a line, or even how it was inherited. Now we know that it is autosomal recessive, and that it is something that can be bred out of Rat Terriers IF we test and are careful not to cross carriers. 

Canine Lens Luxation Basics 

Order NEW-EASY DNA test for your dog 

Part 1 - Managing the Carriers by Carmen Battaglia- Symbol Pedigrees