Common names or abbreviations:
Description or definition:A cataract is a cloudiness to the lens of the eye that causes light to scatter as it enters the eye. The scatter of light may initially only result in blurry vision, but may eventually progress to cause blindness. The opacities can range from minute areas that are barely detectable to complete cataracts in which the lens suffers a total loss of light transmission, resulting in blindness. There are many causes of cataracts including: genetic conditions, aging degeneration, birth defects, diabetes, nutritional, electric shock, and trauma. They can also be secondary symptoms to other eye diseases. Heritable cataracts are noted in younger animals (as early as 6 months up to 6 years of age) and affected individuals should be removed from a breeding program and neutered as they may pass the defective gene on to future generations. Older dogs, just as older people may also develop cataracts as an aging degeneration. Cataracts will also develop in all dogs afflicted with diabetes.
In some dogs with diabetes, cataracts may have a rapid onset causing acute blindness. In others, cataract formation may be slowly progressive. Proper control of the diabetes will aid in slowing the onset of cataracts. Electric shock, like from biting electrical cords or lighting strike may also result in cataract formation. These will rarely cause visual impairment. Traumatic injuries to the eye may also result in secondary cataract formation. Traumatic injuries may include a blunt blow to the eye or penetrating injury like from a scratch or thorn.
The exact cause of a cataract observed in an
individual dog is often difficult to determine. Congenital cataracts may
or may not be inherited. Cataracts may be primary or secondary. Primary
cataracts are the type observed when no other ocular abnormality is
present. Secondary cataracts are those that are associated with or
accompany another eye disorder, such as generalized Progressive Retinal
Atrophy (PRA). Genetic cataracts in dogs may be either inherited in a
dominant or recessive mode, or both.
Genetic factors are the most important cause of cataracts in the dog. The age of onset, initial appearance, and rate of a cataract's progression are often predictable for a given breed. The specific pathogenesis (mechanism) of inheritable cataracts in dogs has not been defined, but likely results from a variety of different defects in lens cellular metabolism.
Two characteristics typical of many heritable ocular
disorders are late onset and the presence of carriers. Many heritable eye
problems are not apparent until the animal is middle-aged, between 5 and 9
years old. Consequently, prospective pet owners are unable to detect
a problem when obtaining a puppy. For the same reason, it is difficult for
dog breeders to choose breed stock that is free from potentially heritable
Occasionally a dog or some of its litter mates have signs of a heritable eye disease, although the sire and dam appear normal. In this situation, the parents are considered carriers of the disease. All of the siblings should be considered carriers as well, unless test matings indicate otherwise. The most prudent and appropriate approach is for those presumed carriers to not be used in a breeding program.
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