Symptoms of eye disease are usually noticeable and give you good clues that you need to get your pet to the veterinarian. Squinting is a symptom of pain and is often accompanied by excessive tear production. Excessive green, yellow, or reddish “goop” in the corner of your pet’s eye is another indication of a problem. A bulging eye, red discoloration, or abnormal pupil size are all symptoms of a potential problem.
The most common eye problem that I've seen in veterinary practice is the corneal ulcer. This is a defect in the surface of the cornea (the outer covering of the eyeball). It can be caused by trauma to the eye, decreased tear production, a defect in the cornea’s metabolism, abnormal eyelashes or eyelids rubbing on the eye, or may be unknown. Dogs or cats with a corneal ulcer will squint and have tears running from the affected eye. They may not let anyone touch their face on that side. A diagnosis is made by numbing the eye for the examination and applying a stain to the surface of the eye. The stain will stick to the ulcer, but not to the normal cornea. An ulcer may be very superficial and can resolve within 24 hours of treatment. Sometimes they are much deeper, even down to the very inner layer of the cornea, and may be much more difficult to treat. Entropion is a condition common in certain breeds of dogs (and few cats) where the eyelids have excess skin and actually roll in so the haired surface rubs on the cornea. This constant irritation leads to ulcers. Surgery of the eyelid can be performed to correct this anatomical defect and stop the hairs from rubbing on the eye. Indolent ulcers are chronic, superficial ulcers that are usually caused by a defect in the metabolism of the cornea. They can be encouraged to heal by a procedure that involves numbing the eye and “drawing” a grid on the ulcer and surrounding normal cornea with a small needle. The grid looks like a tic-tac-toe board. This procedure will help the ulcer heal, but they do tend to recur. Treatment can be as simple as some drops applied to the eye for a few days or as complex as a surgical procedure to help protect the defect while it heals.
Cataracts are another relatively common problem for dogs, but not for cats. Cataracts result from a change in the composition of the protein material inside the lens of the eye. This can occur over time as an age-related change or quickly as a result of a medical condition such as diabetes. Whatever the cause, complete cataracts cause blindness. Light is completely blocked from reaching the retina (the back of the eye) so the brain does not get any signals from the optic nerve that sits in the center of the retina. Surgical removal of the cataracts is possible. The cataract is emulsified by a high frequency vibration from a surgical probe inserted into the lens capsule. An artificial lens can even be inserted into the remaining capsule to improve the vision after surgery. Cataracts that are untreated for long periods of time can become hypermature. When this occurs, they are prone to leak into the chamber of the eye and cause inflammation and pain. Dogs that are blind can adapt to this condition. It is important to keep their environment as stable as possible and certainly not to let them wander outdoors unattended.
Glaucoma is the elevation of the pressure inside the eye, or intraocular pressure. It can be a result of increased production of the fluid inside the eye, but usually is a result of decreased drainage of the fluid from inside the eye. This fluid, or vitreous, is constantly produced and must be able to drain from the eye so that the pressure remains normal. It usually affects one eye at a time. This serious condition can quickly lead to blindness if untreated. In dogs, the problem is usually primary, with no underlying cause. It is related to breed, and can be inherited. In cats, the problem is usually secondary, with a problem such as trauma, inflammation, or neoplasia (cancer) causing the glaucoma. Often, medications must be administered orally and/or intravenously as well as on the surface of the eye itself. It is very important that the normal eye is treated to help prevent the problem from affecting this eye as well.
Keratoconjunctivitis sicca (KCS), or dry eye as it is commonly known, is a condition that results from decreased tear production. This can be caused by different medications, damage to the glands that produce the tears, or destruction of the gland by inflammatory cells in the body. What results is exactly what it sounds like, a dry eye. The surface of the cornea remains moist from the lubricating action of the tears and the blinking mechanism. When tear production is abnormally low, the surface of the cornea dries out and becomes susceptible to ulceration. Usually there is build-up of sticky mucus in the corners of the eyes. Immunosuppressive medications are applied to the eye to help stop the inflammatory reaction in the tear glands. Artificial tears can be used additionally to help lubricate the cornea.
Uveitis is inflammation in the chamber of the eye. It can occur in front of the lens and is called anterior uveitis or can occur behind the lens and is called posterior uveitis. Inflammatory cells accumulate in the chamber and in the cornea and make the eye appear cloudy or even blue. Uveitis can result from a systemic illness or from a problem with the eye itself. Cataracts often cause secondary uveitis because proteins leak from the abnormal lens and attract inflammatory cells to the inside of the eye. Intraocular pressures are lower than normal. Treatment of the underlying disease or inflammatory process as well as treatment of the eye itself will help resolve uveitis.
Retinal degeneration is a common disease in older dogs. The retina (responsible for eyesight) actually deteriorates over time and vision can be completely lost. There is no known treatment to delay the progress of the disease or correct it once it’s diagnosed.
Retinal detachment is a result of hypertension (high blood pressure) or trauma and is seen most commonly in cats. The increased pressure in the vasculature actually allows the retina to peel away from the back of eye and it can be seen “floating” in the posterior chamber or back of the eye. This interferes with the ability of the pet to see. The retina may reattach when the underlying problem is corrected, but vision deficits may still exist.
Iris melanoma is a condition that usually affects older cats. Black spots on the iris (colored part of the eye) can be simple pigment spots, or they could be iris melanoma. Iris melanoma is a malignant type of cancer and should be removed. A veterinarian can monitor the black spots for change in shape or size and can also monitor the intraocular pressure to determine whether or not the eye should be removed.
There are many types of cancers that can affect various parts of the eye. Eyelid tumors are the most likely type that you would see on your pet. Many of these are benign and can be surgically removed when they are small, before they interfere with the function of the eyelids or the surface of the eye.