Cataract in Greek means "waterfall".  The medical term "cataract" refers to an alteration of the fibers or capsule of the lens of the eye.  The alteration, a white opacity, is like turbulent water at the bottom of a waterfall.  Cataracts begin as spots in the lens that look like crushed ice.

The lens of the eye is responsible for about 30% of the focusing power of the eye. Cataracts diffuse the light passing through the lens instead of focusing the light on the retina (back of the eye) for clear sight.  Mature cataracts obstruct transmission of light through the lens causing blindness.  Likewise, when looking into an eye of a dog with a mature cataract, the retina cannot be seen.

Incidence and Causes

Cataracts are among the most common problems of vision in dogs.  All ages, breeds, and sexes of dogs can develop cataracts.  Infections, toxins, UV light, and dietary problems can be causes, but most cataracts in the dog are inherited, due to aging, or caused by diabetes mellitus.  Cataracts are fairly rare in cats.  The most common cause in cats is trauma to the eye. 

The lens is composed of a careful balance of protein fibers surrounded by water.  That balance is maintained by a cellular water pump mechanism.  If the water pump is damaged by injury, disease, or aging, extra water enters the lens and separates the protein fibers causing cataract formation

Inherited cataracts generally appear from birth to one year of age.  Senile (from aging) cataracts and diabetic cataracts appear typically after 8 years of age.  Senile cataracts develop slowly, while diabetic cataracts tend to appear suddenly.

Examples of some breeds at risk for inherited cataracts include cocker spaniels, Boston terriers, golden retrievers, Labrador retrievers, miniature schnauzers, Staffordshire bull terriers, standard poodles, and springer spaniels.

Signs and Symptoms

Cataracts are not the only condition that causes "greying" of the lens.  A normal aging change called nuclear (or lenticular) sclerosis occurs in most older dogs as the lens fibers loose their elasticity and compression.  Nuclear sclerosis does not significantly affect vision.

Cataracts initially cause only dimmed vision but can advance to obscure the vision completely when mature.  Signs in dogs, besides the whitening appearance of the eye, include bumping into objects, particularly when the surroundings are not familiar.

Diagnosis

The diagnosis is made by an ocular examination performed by a veterinarian.

Treatment

There is no medical treatment for cataracts.  Once they develop, cataracts are permanent.  However, a cataract-containing lens can be surgically removed and vision restored.  A common technique is to suck out the inside of the lens and then refill its capsule with an intraocular artificial lens.  After cataract surgery, dogs can see well but not perfectly.

Developing cataracts elicit an inflammatory reaction in the eye (uveitis) that can cause other problems such as glaucoma or detached retina.  If surgery is not performed, anti-inflammatory medications are needed for the remainder of the dog's life to minimize the risk of dangerous reactions in the eye.

For more information, contact your local veterinarian or the MU Veterinary Medical Teaching Hospital 573-882-7821 or visit http://www.vmth.missouri.edu/

C.B. Chastain, DVM
Professor, University of Missouri
College of Veterinary Medicine