Pannus (Chronic Superficial Keratitis)

Pannus, or chronic superficial keratitis, is a progressive inflammatory autoimmune disease of the cornea. Common clinical signs include pigmentation (brown discoloration), vascularization (blood vessel in-growth) and opacification (haziness) of the cornea. These corneal changes may lead to scarring and may progress to severe visual impairment or blindness in severe cases. Active disease may also result in discomfort.

Cause

The definitive cause of pannus is not known, but several factors may be involved:

1. An increased incidence in certain breeds (German Shepherd dog, Greyhound, Labrador Retriever, and Border Collie) suggests a genetic predisposition.
2. Ultraviolet radiation and high altitude increase the severity of the disease; therefore, dogs living at high altitudes and very sunny areas are often more severely affected with the disease that is more difficult to control. It is most common in the desert southwest and the Rocky Mountain States.
3. Immunological factors are believed to contribute. Pannus is considered a form of an autoimmune disease, in which the body directs an inappropriate immune response against the tissues of the cornea.

Signs

The cardinal sign of pannus is vascular or pigment infiltration into the clear cornea, causing whitish, pink or brown discoloration. This typically starts at the outside edge of the clear cornea nearest to the ear and extends inward. The blood vessel in-growth and pigmentation of the cornea may progress across the entire corneal surface and if left untreated, may result in blindness.

Diagnosis

A diagnosis of pannus is usually made on the basis of characteristic clinical signs but sometimes additional diagnostics, including cytology and bloodwork, are recommended.

Treatment

Despite intensive research efforts, no permanent cure exists. The good news is that the vast majority of cases can be managed with topical medications that halt the disease progress and reverse corneal damage. This condition does, however, require lifelong treatment with the best outcomes seen when therapy is instituted early in the course of the disease. The inflammatory cell infiltrations and the vessel invasion usually are reversible with therapy. On occasion, the scarring and pigment depositions are not irreversible but they can often be minimized with regular treatment. Even short periods of interrupted therapy, for example 2 to 4 weeks, may cause severe recurrence with profound effects on your dog’s vision.
There are three categories of therapy:

1. Corticosteroid therapy may be administered by intermittent injections under the conjunctiva (pink mucous membrane of the eye) and/or by topical application of eye drops or ointments.
2. Topical immunomodulatory therapy in the form of topical cyclosporine or tacrolimus combined with steroids provides the best possible control of pannus in approximately 85% of dogs with this condition. Frequency of topical medication may vary throughout the year based on levels of UV light.
3. In patients that do not respond to topical medications, more invasive techniques may be recommended. Surgical excision of a superficial layer from the affected area may restore vision in eyes that have extensive scarring and pigmentation. This is called superficial keratectomy. Unfortunately, the post-operative recurrence rate is high and this method remains a last resort.
4. Beta-irradiation has been used when medical therapy alone is insufficient. Potential complications associated with the use of these medications include, but are not limited to, inflammation of the pink tissue (conjunctivitis) and corneal ulceration, corneal mineralization; some of these complications can lead to blindness if not promptly addressed.

Your awareness of your pet’s symptoms and compliance with recommendations for medication and recheck examinations help control these potential complications.

If you have any further questions about pannus or any other ocular condition, please do not hesitate to call us at Eye Care for Animals.