Cataracts in Dogs
A normal lens, which sits behind the pupil, is transparent and focuses light onto the retina. The retina sends the image to the brain, where vision is perceived. When the cells and the protein of the lens begin to deteriorate, a cataract forms. The lens gets cloudy and the light cannot be transmitted to the retina.
Cataract formation is one of the most common eye diseases in dogs, which, according to the American College of Veterinary Ophthalmologists, affects about 97 breeds in which inheritance is suspected. However, only 15 additional breeds are named as having proven cataract with a known mode of inheritance, the majority being autosomal recessive.
The breeds with the highest cataract prevalence include: Smooth Fox Terrier, Havanese, Bichon Frise, Boston Terrier, Miniature Poodle, Silky Terrier, Toy Poodle, American Cocker Spaniel, Standard Poodle, and Miniature Schnauzer.
The degree if vision impairment is determined by the size and location of the cataract within the lens (although even small cataracts may produce sufficient glare from scattered light to induce squinting).
Cataracts are usually classified by the cause into three main groups:
- primary hereditary
- secondary
- other cuases
Most cataracts in dogs are inherited; less commonly, cataracts can be secondary to trauma or other eye diseases, including uveitis, glaucoma, lens luxation and retinal degeneration, or secondary or underlying systemic metabolic disease, including diabetes (cataracts are obeserved in almost 40% of diabetic dogs) and Cushing's disease.
Congenital cataracts (present at birth) may or may not be inherited and generally do not progress to blindness, although in puppyhood such a cataract may represent a visual handicap.
TREATMENT Cataracts are readily amenable to surgical intervention, with excellent results in terms of restoration of vision and replacement of the cataractous lens with a synthetic one. The procedure used is called phacoemulsification and involves a machine that emits high-frequency sound-waves that destroy the lens. A suction device then removes the lens particles from the eye. An artificial lens called IOL (intraocular lens implant), replaces the old lens. The success rate is over 90%. Surgery takes one hour per eye.
PREVENTION Recent studies show that nutrition plays in important role in preventing or delaying cataracts in older dogs. It has been observed that natural antioxidants, such as wheat sprout powder induces in old dogs a significant reduction of age-related cataracts.
Potential breeding stock should be evaluated by the Canine Eye Registration Foundation (CERF) which will issue a clearance certificate for all uneffected dogs.
A CERF examination will detect hereditary eye problems, such as cataracts and PRA (progressive retinal atrophy), a disease causing retinal degeneration and irreversible blindness. It may occur as secondary disease to cataracts. If so, cataract surgery cannot restore vision, because the retina has become nonfunctional.
CATARACTS IN OLDER DOGS
The slight haziness that appears in an older dog's pupils is normal and has minimal effect upon vision. Cataracts are quite common in older dogs. Dogs with cataracts generally do very well until the last stages of opaqueness. Even though they can't distinguish sharp edges and small shapes, they can follow general movements and actually compensate very well.
It is when the cataract becomes severe that you'll notice the dog losing all sight. Some people call any cloudiness of the lens in old dogs a senile cataract, when in reality it is a condition called Nuclear sclerosis. Nuclear sclerosis occurs when, over time, the fibers of the lens become more dense and light is reflected off the back of the lens capsule. This gives the lens a cloudy appearance, which looks very much like a cataract— but it is not. Nuclear sclerosis will not cause complete blindness. It does affect the dog's vision, however. These dogs learn to watch for blurred, unfocused movement and rely more on smell, sounds and vibrations for their sensory input.
References:
1. Nutritional relevance of wheat sprouts containing high levels of organic phosphates and antioxidant compounds. Marsili V, Calzuola I, Gianfranceschi GL.
2. Dr. Carol's Naturally Healthy Dogs by by Dr. Carol Osborne
Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.
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