Keratitis is inflammation of the cornea in which the cornea becomes cloudy, resulting in loss of transparency. The signs are excessive tearing, squinting, pawing at the eye, avoiding light, and protrusion of the third eyelid. There are different types of keratitis; all are serious diseases and can lead to partial or complete blindness. All types of keratitis must be treated by a veterinarian.
Ulcerative keratitis is a painful corneal inflammation that occurs as a complication of keratoconjunctivitis sicca or corneal ulcer. The cornea appears dull and hazy, then cloudy, and finally milky white and relatively opaque. Treatment is similar to that described for Corneal Ulcer (page 192).
Infectious keratitis occurs when a bacterial infection complicates ulcerative keratitis, keratoconjunctivitis sicca, or corneal ulcer. The most common invading bacteria are Staphylococcus, Streptococcus, and Pseudomonas. In addition to
eye pain, infectious keratitis is characterized by a purulent discharge from the eye. The eyelids are swollen and matted. This might, at first, suggest conjunctivitis (which could seriously delay diagnosis and treatment), but conjunctivitis is not usually accompanied by signs of a painful eye.
Treatment is similar to that described for Corneal Ulcer. It is important to use topical antibiotics selected following culture and sensitivity tests.
Fungal keratitis is uncommon in dogs, but may occur with the prolonged use of topical antibiotics. The diagnosis is made by fungal culture. It is treated with antifungal drugs.
Interstitial keratitis (blue eye) is a corneal inflammation in which a bluish-white film appears over the clear window of the eye. It is caused by the same virus that causes infectious hepatitis, and at one time it occurred after vaccination with CAV-1 (vaccines with this version of the hepatitis virus are no longer used). Signs appear 10 days after exposure. The eyes begin to water and the dog squints and avoids light. Most dogs recover completely within a few weeks. In some cases the eye remains permanently clouded.
Vascular keratitis is caused by neovascularization – the process by which the transparency of the cornea is lost due to an ingrowth of blood vessels and connective tissue. You can see blood vessels growing onto the cornea with your naked eye.
Pigmentary keratitis results when melanin pigment is deposited in the cornea. This is a separate process, but is often associated with vascular keratitis. Both conditions interfere with vision and may progress to blindness.
Vascular and pigmentary keratitis may, in some cases, be the result of a chronic corneal irritation such as that caused by entropion or lagophthalmos (inability to completely close the eyes). Removing the initiating process may reverse the keratitis.
Pannus is a specific type of nonpainful pigmentary keratitis found in German Shepherd Dogs and their crosses, and also in Belgian Tervurens, Border Collies, Greyhounds, Siberian Huskies, Australian Shepherds, and other breeds. It occurs in dogs over 2 years old. An immune-mediated disease is suspected to be the cause. Pannus may be associated with dogs who live at high altitudes, due to the decreased ozone layer. A distinguishing feature of pannus is redness and thickening of the third eyelid, but this may not always be present.
Treatment: Vascular and pigmentary keratitis that are not related to chronic eye irritation are progressive and incurable. The goal of treatment is to arrest the disease and maintain remission.
Neovascularization responds well to high-dose topical corticosteroids. These preparations must be monitored closely by your veterinarian, because prolonged use of corticosteroids in the eyes can lead to a mild form of Cushing’s syndrome and other problems. Improvement begins in two to six weeks. Treatment is life-long. Stopping the eye drops even for a short time is followed by relapse. Only a low dose may be needed for maintenance.
Ophthalmic cyclosporine instilled into the eyes twice daily may reduce the deposition of melanin pigment.