Disorders of the Cornea in Dogs
The cornea is the clear dome on the front surface of the eye. It helps to protect the front of the eye and is also important in focusing light on the retina at the back of the eye. Because the cornea is critical for proper vision, it is important to address any disorders or injuries promptly.
Inflammation and swelling of the outer cornea is common in all species. The most common sign is the development of blood vessels in the cornea. In addition, the cornea often becomes cloudy due to fluid build-up, cellular infiltrates, pigmentation, or the formation of fibrous tissue. If slow-healing sores (called ulcers) are present, pain—shown by watering eyes and spasmodic winking—is common. Bacterial infections can worsen corneal ulcers. If inflammation and swelling of the cornea is in one eye only, injury or trauma is often the cause. Your veterinarian will also check for other factors, such as abnormalities in the shape, outline, or form of the eyelid and foreign objects. This check is important because your dog’s condition will not improve until any such conditions are under control.
Inflammation and swelling of the outer cornea in both eyes may be caused by a response from the immune system or may be associated with a lack of tears; abnormalities in the shape, outline, or form of the eyelids; or infectious agents.
Pannus, or Uberreiter disease, is a rapidly spreading, longterm inflammation and swelling of the surface of the cornea in both eyes. The disease begins on the edge of the cornea where the cornea and the white of the eye meet. It eventually spreads from all edges to cover the cornea. It is common in German Shepherds, Belgian Tervurens, Border Collies, Greyhounds, Siberian Huskies, and Australian Shepherds. The signs and amount of inflammation seen can change with age, season, and amount of time the dog spends outside. Treatment for pannus consists of topical corticosteroids and/or cyclosporine (usually given as eye drops). Because this disease is caused by the immune system, treatment needs to be continued for the rest of your pet's life. Any underlying or concurrent conditions, such as bacterial infections or dry eye, will also need to be treated. Routine veterinary examinations are needed to monitor your pet’s response to the treatment and make adjustments as required.
Inflammation and swelling within the cornea involves the deep connective tissue that provides the structure of the cornea. It is referred to as interstitial keratitis. It is present in all longterm and in many short-term, severe cases of inflammation of the lining within the front of the eye. Swelling of the cornea is often very noticeable. Some generalized diseases can cause this type of inflammation in one or both eyes. These diseases include infectious canine hepatitis, whole system diseases caused by fungi, and diseases caused by toxic microorganisms in the bloodstream. In these cases, therapy is directed at the inflammation of the eye, the generalized infection, or both. Your veterinarian will prescribe the most effective treatment for your pet.
Inflammation and swelling of the cornea with slow-healing sores (ulcers) may occur on the surface of the cornea (superficial) or they may be deeper. When deep ulcers occur, the membrane that covers the inner surface of the cornea may protrude through the cornea, or the ulcer can create a full-thickness hole in the cornea. In dogs, most ulcers are caused by injury, such as nail scratches, foreign objects in the eye, or chemicals that enter the eye. Pain, irregularity of the cornea, swelling, and eventually development of blood vessels are signs of ulceration. Infection is another cause of ulcers; however, bacterial infection often occurs after the ulcer is already present. A dense, white material at the edge of the ulcer indicates the presence of white blood cells and bacterial involvement.
To detect small ulcers, a veterinarian may put drops of a specialized dye into the eye. Therapy for shallow ulcers usually consists of topical antibiotic(s) and correction of any causes, such as removal of a small splinter from the eye. The ulcers usually heal within a week. Another topical medication called atropine may be used to dilate the pupil and reduce eye pain. However, atropine may reduce tear production. Your veterinarian will prescribe the most appropriate combination of medication and other treatments to control the condition.
Syndromes of very slow-healing and recurrent shallow ulcers occur in dogs, especially in older animals. They may be due to a membrane disease causing faulty attachment of the thin layer of cells lining the cornea or due to a virus called herpesvirus. Initial therapy often includes removal of the dead, damaged, or infected tissue of the ulcer by a veterinarian, followed by prescription eye medications. For resistant cases, surgery may be required to stimulate new membrane growth. Nictitating membrane flaps (or soft contact lenses or collagen shields) may be used as a pressure bandage.
Medical treatment of deep ulcers is similar to that of shallow ulcers, but many deep ulcers also require grafts of conjunctival tissue to strengthen the cornea.
Deterioration in the structure and function of the cornea occurs frequently in dogs. Corneal dystrophies (abnormal form or structures) that occur in both eyes are likely inherited or breed-predisposed in dogs, and often consist of triglyceride and cholesterol deposits within the connective tissue of the cornea. Treatment for these deposits is not usually necessary unless they affect vision or become irritating. Corneal dystrophy that affects the deepest portion of the cornea can cause swelling and pain and should be treated early on with eye medications; more advanced cases may require surgery.
Corneal degenerations often occur in only one eye and are usually the result of other eye or generalized diseases. Triglyceride, cholesterol, and calcium deposits may be present. Treatment involves managing the systemic disease, if one is present. High-fat diets can lead to elevated levels of fats in the blood and corneal degeneration in both eyes. These dogs are treated by changing the food to one lower in fat.
Also see professional content regarding the cornea.