This is the most common hereditary disorder in Jack Russell Terriers. Although this is more prevalent in terrier breeds than in any other breed, it does not mean that it is common. It is important that breeders have their dogs tested so that they will not breed dogs that will pass this condition along. It is important that owners should be aware of it before they adopt a purebred dog, or in case it happens to their dog.
Lens Luxation is when the lens of one or usually both eyes becomes displaced. If it happens to one eye, it will eventually happen to the other. In severe cases the dog’s eye may have to be removed, however, the dog can survive.
This condition can appear suddenly, or you may notice the dog having problems seeing. It is most common in terriers between ages of 3 to 8 years old.
The displaced (luxated) lens falls out of its normal place behind the pupil when the ligament fiber which holds the lens in place deteriorates. Subluxation is the partial separation, and is often times an indication of an eventual total luxation.
The lens can be displaced to the rear, which is the posterior. In this case, the eye will appear normal.
However, you may notice a difference in your dog’s behavior. If your dog starts bumping into things or missing the first step of the staircase, you need to get his eyes checked by a veterinarian.
If the lens is displaced forward, this is anterior luxation. This is more severe. The lens will rub against and irritate the cornea, causing tearing and a bluish cast over the eye. Anterior luxation has a high probability of causing glaucoma. If the lens touches the cornea it will cause damage leading to cornea edema. Take your dog to the veterinarian immediately because the lens now restricts the flow of ocular fluids, creating eye pressure and great discomfort.
The treatment needed will vary according to the severity of the disorder. Surgical removal of the lens will alleviate pain and can allow partial vision. However, this surgery is expensive and is not always effective. Sometimes a combination of eye drops and oral medication can help.
It is thought that primary lens luxation (PPL) is only carried forward if both parents are carriers of the disorder. If both parents are carriers, all of the offspring will also be carriers.
Secondary lens luxation is not a hereditary disorder. It is associated with trauma to the eye, such as puncture or injury.
The CERF test was created to test for heritable eye diseases in order to reduce the chance of passing these diseases along. All terriers that will be bred should be tested before breeding. They should be tested within one month before breeding since problems may have developed since a test that is one year old. Some people ask, “Why is the CERF test only valid for one year?” The main reason is that some of these conditions do not appear or test positive until the dog is older. For more information on particular eye diseases that show up later, click here.
A CERF test is a painless examination of the dogs eyes. CERF the Canine Eye Registration Foundation maintains a registry for dogs tested by certified ACVO (American College of Veterinary opthamologists) for major heritable eye disease. Click on this link to find a clinic that administers the CERF test near you.
Glaucoma is increased pressure within the eye. Glaucoma usually leads to partial or total blindness. So the sooner this is treated the better. Early signs to watch for include the dog rubbing his eye with his paw, rubbing his eye against you, or rubbing his eye against the furniture or carpet. Don’t think this is just a common thing and let it go unnoticed. Other signs include fluttering of eyelids, or squinting with one eye. The cornea may look cloudy, or the blood vessels in the white portion of the eye may increase in size. The pupil of the affected eye will usually dilate in the early stages of the condition. It may still react to changing light, but will react more slowly. Glaucoma usually initially affects just one of the eyes. If the pupil in one eye is larger than the other, something is definitely wrong.
Corneal dystrophy affects the opacity of the clear surface of the eye. In most breeds, corneal dystrophy appears as gray-white, crystalline or metallic opacities in the center of the cornea or close to the edge. This disorder is uncommon in Jack Russell Terriers. It is more common in Airdale Terriers and Boston Terriers in which the progression may be rapid and lead to blindness.
Progressive Retinal Atrophy (PRA)
PRA is the deterioration of the visual receptors of the retina. This is actually a name given to a group of hereditary retinal diseases in dogs. Almost all forms of PRA eventually lead to complete blindness. This disease also occurs in mixed breed dogs.
The first sign of most types of PRA is night blindness. Dogs will often bump into objects in a dimly lit room; a room in which a person can see well enough to avoid the object. Gradually dogs with PRA will lose their ability to see in well lighted rooms and will go completely blind. They will frequently have dilated pupils. Sometimes owners will notice increased shininess or hyper-reflectivity to the back of the eye.
According to the CERF website, an important test done by ophthalmologists to diagnose PRA is an electroretinogram (ERG). This test detects the small electrical signals given off by the cells of the retina when they respond to light. The ERG is done by placing a contact lens on the eye and 2 small electrodes on the head. A bright light is then flashed into the eye. If the retina is normal, a distinctive signal is given off by the retina which is amplified and measured on a computer. If the retina is abnormal, the signal will be reduced in amplitude.
PRCD (progressive rod-cone degeneration) is the most widespread form of PRA and affects many breeds including poodles, American and English cocker spaniels, Labrador retrievers and Portuguese water dogs. The rods and cones in the eye can start to degenerate at one year of age and the dog can be totally blind by the time he is 3 to 5 years of age.
A marker-based test for PRCD has been developed by the researchers at the James A. Baker Institute. This test can be used for Portuguese water dogs, Chesapeake Bay retrievers, English cocker spaniels and Labrador retrievers. This test is based on the fact that the researchers have found a set of genetic markers on the canine chromosome 9 that usually indicate the presence of the gene mutation that causes PRCD.