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| Friday, July 28, 2006 |
| Cataracts. Opacity in the lens ... |
Cataracts are an important cause of blindness in the dog. Through special surgery, it may be possible to restore vision. Would you recognize a cataract if you saw one in your cat or dog?
WHAT IS A CATARACT?
The normal lens of the eye is a focussing device. It is completely clear and is suspended in position by special tissue fibers (called “zonules”) just inside the pupil. The lens focusses an image on the retina in the back of the eye in a process called “accommodation.” The focussing power of the dog’s lens is at least three times weaker than that of a human and a cat’s lens is at best half the focussing power as a human’s. (It is helpful to remember that dogs and cats have a sense of smell at least 1000 times more accurate than ours and this is their primary means of perceiving the world.)
Despite its clarity, the lens is in fact made of tissue fibers. As the animal ages, the lens cannot change it’s size and grow larger; instead, it becomes more compact with fibers. This condition is called “nuclear sclerosis” and is responsible for the cloudy-eyed appearance of older dogs but these lenses are still clear and the dog can still see through them; these are not cataracts. The lens is enclosed in a capsule which, if disrupted, allows the immune system to see the lens proteins for the first time, recognize them as “foreign,” and attack. The resulting inflammation is painful and can be damaging to the eye.
A cataract is an opacity in the lens.
Cataracts can be congenital, age-related, of genetic origin (the most common cause), caused by trauma, by dietary deficiency (some kitten milk replacement formulas have been implicated), by electric shock, or by toxin. The patient with a cataract is not able to see through the opacity. If the entire lens is involved, the eye will be blind.
More information at thepetportal.org
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posted by SGPETS @ 8:42 PM  |
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