By Dr. Becker
You've probably heard the old adage, "The eyes are the windows to the soul." That may or may not be true, but what we know for certain in veterinary medicine is that you can tell certain things about the health of animals by carefully examining their eyes.
A number of immune-mediated, infectious, and metabolic diseases, as well as high blood pressure and tumors can be detected, or at least suspected, by the way they show up in a dog's or cat's eyes.
Ocular Signs of Immune-Mediated Disease
Infectious canine hepatitis is an autoimmune disease caused by the adenovirus. Fortunately, the condition is rarely seen today in the U.S. because we vaccinate against it. But both the infection and the vaccine can cause the eye conditions known as interstitial keratitis and uveitis.
Interstitial keratitis, also known as blue eye, is chronic inflammation of the cornea that causes a bluish-white film to form over the cornea. Uveitis is inflammation of part or the entire uveal tract of the eye, which includes the iris, ciliary body, and choroid.
If the condition is vaccine-induced, it will develop in about 10 days to two weeks after vaccination. You might notice your dog is suddenly light sensitive, is squinting uncontrollably, or that his pupils are constricted (narrowed). Within a day or two after uveitis develops, the corneas of the eyes will begin retaining fluid and will take on a blue or cloudy appearance.
Another immune-mediated disease with ocular signs is uveodermatologic syndrome, which is seen most often in the Akita, Australian Shepherd, Beagle, Chow Chow, Samoyed, Siberian Husky, Alaskan Malamute, and related mixed breeds.
In uveodermatologic syndrome, the dog's body attacks its own melanocytes, which are the cells that produce pigment primarily in the skin, the retina, and the uveal tract of the eye. It's not known what causes the condition, but speculation is that a virus of some sort is involved.
Usually, the first ocular sign pointing to uveodermatologic syndrome is uveitis, which ultimately leads to blindness. You might notice your dog's eyes are bloodshot or seem to be causing her pain. She may bump into objects and show other signs of a problem with her vision. Her pupils will be constricted, and her eyes may appear cloudy or as if they've changed color.
Within three to six months after eye problems begin, 90 percent of affected dogs will have whitening of the coat, which is sometimes confined to the face. In about 50 percent of dogs, the skin will also whiten, and will be most obvious on the eyelids, nose, lips, footpads and scrotum.
Ocular Signs of Infectious Disease
- Conjunctivitis ("pink eye")
- Subconjunctival hemorrhage, an area of deep red below the conjunctiva
- Anterior uveitis (inflammation of the ciliary body or iris), or posterior uveitis (inflammation of the choroid)
- Retinal hemorrhage
- Optic neuritis (swelling of the optic nerves)
The fungal disease histoplasmosis can cause:
- Blepharitis, which is inflammation of the outer skin and middle portions of the eyelid
- Chorioretinitis (inflammation of the choroid and retina)
- Granulomatous retinal detachment
- Optic neuritis
The majority of cats (79 percent) with uveitis also test positive for toxoplasmosis.
Ocular Signs of Metabolic Disease
Dogs with diabetes mellitus have many more eye-related complications than cats do. The most common problem in dogs with the disease is the development of cataracts in both eyes. The cataracts come on rapidly and can lead to severe lens-induced uveitis. Diabetic dogs are also more prone to keratoconjunctivitis sicca (dry eye) and reduced corneal sensitivity.
Dogs with Cushing's disease, also called hyperadrenocorticism, tend to develop surface eye lesions including corneal ulceration, corneal degeneration, and dry eye, as well as lesions inside the eye. Cushing's dogs are also at higher risk for sudden acquired retinal degeneration than other dogs.
Another metabolic disease with ocular manifestations is canine hypothyroidism. Dogs with this condition can develop corneal lipid dystrophy, which is a buildup of lipid and calcium within the cornea. The condition can also cause lipemic aqueous humor that turns the fluid in the front part of the eyeball cloudy, uveitis, and retinal bleeding and detachment. Dogs with hypothyroidism are also more prone to develop non-healing corneal erosions.
Ocular Symptoms in Pets with High Blood Pressure (Hypertension) and Neoplasia (Tumors)
Hypertension in dogs and cats can cause a variety of eye problems, including edema (fluid accumulation) of the optic nerve and retina, retinal hemorrhage, vitreal hemorrhage, hyphema (blood in the front of the eye), and retinal detachment.
In a pet with metastatic (spreading) tumors, ocular signs can include conjunctivitis, uveitis, hyphema, and retinal edema. In 25 percent of animals with uveitis, the cause is neoplasia, and over 75 percent of cancer-related uveitis is lymphosarcoma. Hemangiosarcoma and adenocarcinoma are also known to metastasize to the eyes.
Keeping an Eye on Your Pet's Eyes
Because a number of serious canine and feline diseases cause symptoms that affect the eyes, it's important to report any changes or difficulties your dog or cat is experiencing with her vision to your veterinarian.
Any change in the color of the eyes, including a pink or red discoloration, or any behaviors your pet exhibits that indicate her eyes may be bothering her or that her vision has changed, are cause for concern and should be investigated sooner rather than later.