Cataracts

created at: 2010-04-15

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:

Congenital - present when the eyes open or before 8 weeks of age
Juvenile or Developmental - young animals up to about 4 years of age
Late onset - mature animals.

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.

Afghan Hound (early developing cataracts progressing to visual impairment by 2 - 3 years of age)
Akita (cataracts associated with microphthalmia)
Alaskan Malamute (juvenile)
American Cocker Spaniel (juvenile)
Australian Cattle Dog (blue heeler)
Australian Shepherd (congenital, juvenile, adult)
Basenji (congenital)
Beagle (congenital)
Bearded Collie (juvenile, adult)
Bedlington Terrier (juvenile)
Belgian Sheepdog (cataracts non-progressive, do not cause visual impairment)
Belgian Tervuren (non-progressive, do not cause visual impairment)
Bichon Frise (juvenile)
Border Collie (adult)
Boston Terrier (early onset cataracts, bilateral, progress to complete cataract and blindness by 2 - 3 years of age, and later onset cataracts, only occasionally interfere with vision, seen before 8 years of age)
Bouvier des Flandres (congenital, juvenile, adult)
Brussels Griffon (adult)
Cavalier King Charles Spaniel (early onset cataracts appear by 6 months, progress to complete cataract and blindness by 2 years)
Chesapeake Bay Retriever (cataracts seen as young adult, may progress to impair vision)
Chow Chow (congenital cataracts)
Clumber Spaniel
Collie (rough and smooth - congenital)
Curly-coated Retriever (cataracts develop as adults and progress slowly)
Dachshund
Dalmatian
Doberman Pinscher (cataracts develop before 2 years of age and may cause significant vision loss)
English Cocker Spaniel (juvenile)
English Springer Spaniel (congenital, juvenile, adult)
German Shepherd (congenital or early developing cataracts that are non-progressive after 1 or 2 years of age)
German Short-haired Pointer (juvenile)
Golden Retriever (cataracts develop at varying ages, and at different lens locations, usually without visual impairment)
Gordon Setter (juvenile or adult)
Great Dane (juvenile)
Havanese
Irish Setter (juvenile)
Irish Wolfhound (juvenile, adult)
Italian Greyhound (juvenile)
Jack Russell Terrier
Japanese Chin
Labrador Retriever (mostly see stationary or very slowly progressive cataracts by 1 to 3 years of age, that do not interfere with vision)
Lhasa Apso (adult)
Lowchen
Mastiff
Miniature Schnauzer (congenital, juvenile, adult, also cataracts in association with microphthalmos)
Newfoundland
Norbottenspets
Norwegian Elkhound (juvenile)
Nova Scotia Duck Tolling Retriever
Old English Sheepdog (congenital, juvenile, adult)
Papillon (juvenile, adult)
Pekingese
Pembroke Welsh Corgi (congenital, juvenile)
Portuguese Water Dog
Rottweiler (juvenile, adult)
Saint Bernard (juvenile)
Samoyed (congenital, juvenile, adult)
Scottish Terrier (adult)
Shar Pei
Shetland Sheepdog
Shih Tzu
Siberian Husky (juvenile)
Smooth Fox Terrier
Soft-coated Wheaten Terrier
Staffordshire Bull Terrier (early onset cataracts are seen by 12 months and progress to blindness by 3 years of age)
Standard Poodle (cataracts are bilateral, symmetrical, and progressive to blindness by about 2 years of age)
Standard Schnauzer (juvenile)
Tibetan Spaniel
Tibetan Terrier (juvenile)
Welsh Springer Spaniel (cataracts develop as early as 8 to 12 weeks of age and progress rapidly, impairing vision)
West Highland White Terrier (congenital, juvenile)
Whippet (adult)
Wire-haired Fox Terrier (juvenile)
Yorkshire Terrier (juvenile)

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.

References:

Mellersh et al., Vet Ophthalmol. 2009 Nov-Dec;12(6):372-8