What is Primary Lens Luxation (PLL)?
The lens of the eye normally lies immediately behind the iris and the pupil, and is suspended in place by a series of fibers, called zonular ligaments. It functions to focus light rays on the retina, in the back of the eye. When partial or complete breakdown of the zonular ligaments occurs, the lens may become partially dislocated (Lens Subluxation) or fully dislocated (Lens Luxation) from the lens’ normal position.
Primary Lens Luxation is a heritable disease in many breeds, including many terrier breeds; Russell Terrier, Bedlington, Fox, Manchester, Miniature Bull, Scottish, Sealyham, Welsh, West Highland White), Tibetan Terrier, Border Collie, Brittany Spaniel, German Shepherd and Welsh Corgi. In these breeds, spontaneous luxation of the lens occurs in early adulthood (most commonly 3-6 years of age) and often affects both eyes, although not necessarily at the same time. Primary Lens Luxation (PLL) is caused by an inherent weakness in the zonular ligaments which suspends the lens.
Lens Luxation can also occur secondary to other primary problems of the eye, including inflammation, cataracts, glaucoma, cancer, and trauma.
What is the Significance of Lens Luxation?
Lens Luxation can lead to inflammation (Uveitis) and Glaucoma (increased intraocular pressure). This can result in painful, teary, red eyes that may look hazy or cloudy. Both Uveitis and Glaucoma are painful and potentially blinding diseases if not identified and treated early.
How is Lens Luxation treated?
In all cases, a thorough eye exam by your veterinarian or a veterinary ophthalmologist is required, with careful evaluation for uveitis and glaucoma. If detected early, surgical removal of the lens can be beneficial. Medical treatment of inflammation and glaucoma in the form of topical and oral medications can relieve much of the discomfort associated with this disease. Primary Lens Luxation may be tested in any breed and is recommended for the (Jack) Russell Terrier breed.
This dog has tested normal/clear for the mutation known to cause Primary Lens Luxation (PLL) in this breed. It can only transmit the normal/clear gene to its offspring.
Carrier/Low Risk This dog has tested as a carrier/low risk for the mutation known to cause Primary Lens Luxation (PLL) in this breed. This means the dog has one normal/clear copy and one mutated copy of the gene, and has a slight (5-10%) risk of developing Primary Lens Luxation. Either the normal/clear copy or the mutated copy of the gene can be transmitted to its offspring.
Affected/High Risk This dog has tested as affected/high-risk for the mutation known to cause Primary Lens Luxation (PLL) in this breed. It is at risk for developing clinical symptoms of PLL at some point in its lifetime, usually between 4-8 years of age. It can only transmit the mutated copy of the gene to its offspring.
What is Spinocerebellar Ataxia (SCA)?
The term cerebellum in Latin means “the little brain.” The cerebellum is the part of the brain responsible for coordinating movements. Ataxia comes from a Greek term meaning “without order”. When the cerebellum cannot coordinate movement, the dog can move, but the movement is poorly coordinated. They are not weak, in fact, often the movements a dog with ataxia makes are too strong. They have a goose-stepping gait and when excited or running, their legs may appear to be going every which-way. Sometimes they have problems with their balance and will fall frequently. In order for the cerebellum to control movement, it needs to get feedback about what the muscles are doing. This feedback comes to the brain through the spinal cord. When there are changes in the spinal cord in a dog with cerebellar ataxia, the disease is often called spinocerebellar ataxia (SCA). Spinocerebellar Ataxia may be tested in any breed and is recommended for the (Jack) Russell Terrier.
What is Degenerative Myelopathy (DM)?
Degenerative Myelopathy is a debilitating disease that causes gradual paralysis in many dog breeds. It is caused by a degeneration of the spinal cord that onsets typically between 8 and 14 years of age. It presents first with the loss of coordination of the hind legs. It will typically worsen over six months to a year, resulting in paralysis of the hind legs. If signs progress for a longer period of time, loss of urinary and fecal continence may occur and eventually, weakness will develop in the front limbs. An important feature of DM is that it is not a painful disease.
Although any dog can be tested for Degenerative Myelopathy, it is possible that the genetic background that predominates in some breeds prevents the development of symptoms even in dogs testing affected/at risk. At this time, OFA is reluctant to recommend testing for members of breeds where the University of Missouri has not yet proven susceptibility to DM through microscopic examination of spinal cords from deceased dogs that exhibited symptoms of the disease. The required evidence of association between the genetic mutation and actual spinal cord evaluations has not been proven in the Russell Terrier breed.
Information obtained from OFA.org