What is Degeneration of the Image Forming Part of the Eye?
The image forming part of the eye is the retina, a layered membrane at the back of the eye made of photoreceptor neurons called rods and cones. Retinal degeneration is a frequent problem in dogs and there are a number of different types. Among purebred breeds, retinopathies are often inherited. The abnormality may be present at birth and cause symptoms in the first year of life, or it may be degenerative and develop in older or middle aged dogs. Most inherited forms of retinal degeneration eventually cause blindness. Progressive retinal atrophy (PRA) is the most common. This term is used to describe a group of slightly different diseases with similar symptoms. Vision loss often begins with night blindness, but will progress over a period of months or years, with cataracts and complete blindness developing in the later stages of the disease. Sudden acquired retinal degeneration (SARD) is another form of retinal degeneration that can develop very suddenly and may cause blindness in a few days or several weeks. Veterinarians don’t know what causes this disease; it is more common in females and could be a related to an autoimmune reaction or a hormone imbalance. Some types of retinal degeneration are age related. Macular degeneration is the most common problem in older dogs. This is degeneration of the central area of the retina, the macula. It often causes milder vision impairment, but it can lead to complete vision loss as well. Decreased vision begins with the central part of the eye, and dogs may have trouble seeing details or small objects.
Many genetic abnormalities in purebred dogs can cause degeneration of the image forming part of the eye. These conditions often result in total blindness. To a lesser extent, parts of the retina can also degenerate with age. There is no cure for any of the many types of retinal degeneration in dogs.
Symptoms of Degeneration of the Image Forming Part of the Eye in Dogs
Take your dog to the veterinarian if you notice any signs of vision loss.
- Nyctalopia – decreased vision at night
- Dilated pupils
- Decreased pupillary response to light
- Gradual vision loss
- Sudden blindness
- Inability to judge distances
- Difficulty climbing stairs
- Missing details such as small objects
Types
Some of the many types of retinal degeneration are listed below, as well as the breed which they are known to affect. Any dog could develop this problem.
Progressive retinal atrophy (PRA) can be classifed into four types:
- Photoreceptor Dysplasia
- Becomes apparent in the first year (autosomal recessive trait)
- Irish settlers, Collies, Norwegian Elkhounds, Miniature Schnauzers, Belgian Sheepdogs
- Photoreceptor degenerations
- Signs develop in the first 3-5 years (autosomal recessive trait)
- Miniature and Toy Poodles, Samoyeds, English and American Cocker Spaniels, Labrador Retrievers, Tibetan Terriers, Akitas, Tibetan Spaniels, Papillons, English Springer Spaniels, Miniature Longhaired Dachshunds
- Photoreceptor degeneration (x-linked trait)
- Siberian Huskies
- Photoreceptor degeneration (autosomal dominant)
- Old English Mastiffs, Bull Mastiffs
Retinal pigment epithelial dystrophy or central progressive retinal atrophy (CPRA)
- Similar to PRA, but degeneration begins in the epithelial layer of the retina
- Labrador Retrievers, Collies, Shetland Sheepdogs, Briards
Sudden acquired retinal degeneration (SARD)
- Signs develop between 7-14 years, more common in females
- Dogs often experience increased appetite and weight gain just before the disease becomes apparent
Age-related macular degeneration
- Usually occurs in dogs over 7, more common in females
- There may be some genetic component, but exposure to environmental factors and overall health play a big part.
Causes of Degeneration of the Image Forming Part of the Eye in Dogs
Most types of retinal degeneration are caused by one of three factors.
- Inherited
- Age-related
- Idiopathic
Diagnosis of Degeneration of the Image Forming Part of the Eye in Dogs
If your dog is developing symptoms of vision deterioration or night blindness, the veterinarian will carefully examine the eye. Retinal degeneration can often be detected with traditional ophthalmoscopy, but electroretinography offers a more complete measurement of retinal function. In some cases of PRA, cataracts may already be present, which can make it difficult to see the retina. In the case of CPRA, changes in pigmentation in the outer layer of the retina can sometimes be diagnosed early, before dogs start to show symptoms, so dogs at risk should be evaluated even if they are not experiencing vision loss. SARD is also diagnosed with these methods, but in most cases vision loss is quite severe before retinal damage can be detected. Older dogs experiencing mild vision loss will be evaluated the same way. Various vision tests may be necessary to determine the range of your dog’s vision and ascertain the extent of damage.
Other potential causes of vision loss will need to be ruled out, such as glaucoma, age-related cataracts, or in the case of SARD’s, brain tumors and inflammation. Blood and urine tests will be necessary to eliminate some possibilities and ascertain the state of your dog’s health. Sedation or anesthetic could be required for dogs that will not tolerate an eye exam.
The veterinarian will need to know your dog’s breed and family history since many forms are inherited. In some cases, dogs can be tested for genes that are known to cause retinal degeneration before symptoms develop. If your dog belongs to a breed with a known inherited problem, this possibility should be discussed with a veterinarian.
Treatment of Degeneration of the Image Forming Part of the Eye in Dogs
There isn’t a cure for retinal degeneration, so diagnosis is mainly aimed at eliminating other potentially treatable forms of vision loss. It’s believed that proactive treatments can have some effect. Vitamin E deficiency is associated with CPRA, so if your dog is at risk for this condition, or is diagnosed early, the vet may recommend high doses. In general, Vitamin E, other antioxidants, and zinc can help to support vision. This would be more effective with a dog developing age-related macular degeneration than a dog with an inherited abnormality, but overall eye health might delay the onset of the disease to some extent.
Recovery of Degeneration of the Image Forming Part of the Eye in Dogs
Many dogs with retinal degeneration will eventually become blind. Blind dogs can still live fulfilling lives, so this isn’t a reason to consider euthanasia, but you may need to make some adjustments to help your dog cope with the new condition. Your dog will have to find his way by spatial recognition, so avoid rearranging your furniture and your yard as much as possible. Walking your dog on a leash will make him feel more secure and help keep him away from cars and other hazards. Think about potential dangers that your dog may miss, like pools, sharp objects, and stairs. Be patient with helping your dog re-learn how to live without his sight and try to act as your dog’s eyes as much as possible.
