A cataract is any opacity or loss of transparency of the lens of the eye. 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.
The opacity may be confined to a small area of the lens or capsule, or it may affect the whole structure. A complete cataract affecting both eyes will result in blindness, whereas small non-progressive cataracts will not interfere with vision. Primary cataracts occur in some breeds; in other breeds the cataract may develop secondarily to another inherited disorder such as progressive retinal atrophy or glaucoma.
Age of Onset: Specific to each breed; classified as follows:
Breeds Affected: 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.
Symptoms: You may suspect your dog is having visual difficulties and/or you may notice discoloration of your dog's pupil(s). Your veterinarian will be able to see the cataract with an ophthalmoscope. Even when not causing visual problems, cataracts may be discovered on a routine ophthalmoscopic exam.
Associated Diseases: 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 observed in almost 40% of diabetic dogs) and Cushing disease.
Congenital cataracts may or may not be inherited and generally do not progress to blindness, although in puppyhood such a cataract may represent a visual handicap.
Late onset: 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. These dogs learn to watch for blurred, unfocused movement and rely more on smell, sounds and vibrations for their sensory input.
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 unaffected dogs.
A CERF examination will detect hereditary eye problems, such as cataracts and progressive retinal atrophy (PRA ), 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.
Genetics of Cataracts: Most cataracts are inherited. Non-hereditary cataracts also occur, as a result of other diseases, trauma, toxicity, or metabolic disturbances.
In studies involving Boston Terriers, Staffordshire Bull Terriers and Australian Shepherds, at least one gene is associated with early-onset hereditary cataracts. This gene, called HSF4 encode a transcription factor, which is responsible for the expression of other genes. What does HSF4 stand for? Heat Shock Factor 4, which means that this gene was first identified as one that is involved in heat sensitivity. Like many other genes, it is likely that HSF4 affects several different aspects of an organism's life. Not surprisingly, additional mutations may likely be found to be associated with hereditary cataracts.
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