Cataracts are opacities in the lens of the eye. Much like with a camera, the lens is the focusing tool of the eye. Opacities in both the lens of the eye and the lens of a camera will lead to a distorted picture. Another way to think about it is to imagine a pair of eye glasses with a blacked out lens. That would certainly make for impaired vision!

Cataracts are classified by:

1. Cause

2. Age of onset

3. Location within the lens

4. Degree of severity

Causes of cataracts

In the medical and veterinary community, cataracts are classified as either primary or secondary. Primary cataracts have no underlying cause. These include those that are congenital (that is to say that the pet is born with them), hereditary (in the family line) or age-related. In young or purebred dogs, most have a genetic basis - a great reason to protect your best friends from a young age with a pet insurance policy from Petplan, since it can cover hereditary conditions.

Secondary causes, on the other paw, are numerous. They are caused by disease processes, such as retinal diseases, chronic uveitis, trauma to the lens, dislocation of the lens and diabetes. Most diabetic dogs will eventually develop cataracts.

Age of onset

This is an easy one. Are the cataracts congenital (meaning that the pet is born with them)? If not, is the patient young or old? If the patient is young, the cataract is described as juvenile. If the patient is old, the cataract is described as senile. Senile cataracts are fairly common, just as they are in older humans.

Location within the lens

Again, this is pretty self explanatory. We note where, within the lens, the opacity or opacities are located.

Degree of severity

Cataracts have several degrees of completeness:


These are tiny, multifocal opacities involving less than 15% of the lens.


These are incomplete opacities that cover more than 15% of the lens. The back of the eye can still be visualized through the lens.


Mature cataracts are complete and the back of the eye cannot be visualized.


These cataracts appear wrinkly and sparkly, and can go on to cause other ocular problems like uveitis.

Cataracts are easy to diagnose, and your regular veterinarian can do that with a thorough eye exam. Your veterinarian will want to make note of the condition and follow their progression through your dog or cat’s life.

Because cataracts cause blindness if both eyes are involved, or can induce other ocular problems, you may consider having them removed, especially since it is covered by most pet insurance policies. Veterinary ophthalmologists can extract the affected lens and put an artificial lens in it’s place. Keep in mind that ophthalmologists prefer to perform surgery on immature-to-mature cataracts, because the eye is still healthy and recovers better than cases where the it is hypermature. The cost to treat cataracts in dogs was $1,751 on average in 2018, according to Petplan claims data.

If you notice your pet’s vision declining, cataracts could be the cause. Ask your veterinarian to check your pet's eyes at your next wellness visit and be willing to discuss the options for keeping your best friend seeing clearly.

Oct 27, 2011
Pet Health

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