The lens of the eye and the cornea function to direct light to the retina, which is the sensitive nerve tissue layer located in the back of the eye. In a healthy eye, the lens is transparent or clear. A cataract is an opacity or cloudiness of the lens that causes light to scatter, interfering with the way light reaches the retina. Cataracts are a common, but not exclusive, cause of vision loss.
A cataract can be partial or complete and may progress slowly or rapidly. Vision is decreased as the cataract increases in size. Cataracts usually begin as small dots and progress to involve larger areas or the entire lens. They can occur in one or both eyes and may occur at different times. Progression of cataracts is variable. Generally, the younger your pet is at the time of cataract development, the more rapidly the cataract will progress. Cataracts caused by diabetes can also develop rapidly.
Cataracts should not be confused with lens sclerosis (nuclear sclerosis), which is a normal aging change that occurs around the age of 7 to 8 years in the dog. Lens sclerosis causes the patient to become “farsighted,” much as humans do around the age of 45 to 50.
Signs and Symptoms
Cataracts vary in appearance. A partial cataract can appear to be small, with gray or white dots or microscopic blisters. More involved cataracts can resemble cracked glass or appear as a haze, a pearly sheen, white streaks, or a completely white lens.
Not all cataracts cause blindness, and small ones may not impair vision significantly. If vision loss develops slowly over a long period of time, your pet may be able to adjust to your home and yard. Pets in familiar surroundings may be able move about even when almost blind because they have learned and memorized their environment. Signs such as bumping into objects, failing to retrieve favorite toys, and fear of being left alone may be signs of vision loss. These are especially significant if they occur in the pet’s home or yard. When there is decreased visual function, cataract surgery may be recommended. Not all patients are candidates for cataract surgery, though.
Whenever your pet is showing signs of a health issue your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from cataracts or another serious condition, a veterinary specialist is available at an ExpertVet certified hospital.
This is a picture of a cat with cataractous lens. The cataract has liquefied and the center of the lens. The arrow shows the center of the lens.
Many cataracts in dogs are caused by genetic factors and are often inherited from their parents. Cataracts can also be the result of an injury to or inflammation within the eye, or other diseases that affect the eyes. Poor nutrition and exposure to certain foods, drugs, or toxins are uncommon causes of cataracts, though they have been reported.
Diabetes is the most common disease associated with cataract development in the dog. Diabetic cataract formation is related to the degree of hyperglycemia (too much sugar in the bloodstream), the activity of lenticular aldose reductase (an enzyme in the eye), and the amount of sorbitol (a sugar alcoholproduced by the breakdown of glucose).
One study found that 50% of diabetic pets developed cataracts within 6 months of diagnosis of diabetes, and 80% by 1 year after diagnosis. Secondary lens-induced uveitis (or inflammation caused by cataracts) develops from leaking of cataract proteins. In diabetics, this lens-induced uveitis can progress rapidly. Rare cases of spontaneous lens capsule rupture have also been seen with diabetic cataracts. Uncontrolled lens-induced uveitis can lead to other problems and should be treated with anti-inflammatory medicines. Depending on the degree of inflammation, a topical (not swallowed) NSAID (for example, flurbiprofen) or steroid (for example, prednisolone or dexamethasone) should be used several times a day.