Pannus, or chronic superficial keratitis, is a slowly progressive disease of the canine cornea, characterized by pigmentation, vascularization, and opacification. The disease is seen predominantly in the German Shepherd dog, but sporadic cases occur in other breeds as well.

Cause
The cause is not known, but several factors are probably involved:

The breed incidence suggests a heritable predisposition.

Ultraviolet radiation plays an important role as an inciting and propagating factor. In keeping with this, dogs living at high altitudes and low latitudes often are more severely affected.

Immunological factors are believed to contribute. This may be an allergic type of reaction against extraneous materials or against the corneal substance itself.

Many infectious agents have been incriminated, but probably none plays any significant role.

Signs
The cardinal sign is infiltration into the clear cornea, causing whitish, pink, or brown opacification. This invariably starts at the edge of the clear cornea and extends inward. The most common location is at the outer, lower corner of the eye.

Initially, redness and brown pigment may be seen in the mucous membrane just outside the edge of the cornea. Whitish infiltrates of inflammatory cells into the cornea ensues, followed by ingrowth of new blood vessels into the normally avascular cornea. Later, connective tissue grows in and finally this is pigmented brown.

In a small number of cases, two other symptoms may occur, simultaneously or one at a time. These are thickening, redness, and depigmentation of the third eyelid and chronic, erosive ulcers of the lower eyelid near the inner corner of the eye.

When acute or progressing, the disease is uncomfortable to the dog. When kept under adequate therapy, the disease normally does not cause irritation.

Diagnosis
The clinical signs usually are typical enough for a diagnosis to be made, especially when seen in a German Shepherd dog.

Treatment
Despite intensive research efforts, no permanent cure exists. However, in the vast majority of cases, the disease progress can be halted and the problem kept stable, especially if therapy is instituted early in the course of the disease. The two initially occurring components, the inflammatory cell infiltrations and the vessel invasion, usually are reversible with therapy, whereas the final connective tissue and pigment depositions often are irreversible once they have occurred.

There are three categories of therapy:

1. Corticosteroid therapy, administered by intermittent injections under the mucous membrane of the eye, and by continuous application of eye drops. This is the main line of defense against progression of the disease and most often suffices. However, therapy must be kept up consistently for the rest of the dog's life. Even short periods of interrupted therapy, for example 2 to 4 weeks, may cause severe recurrence with devastating effects on the dog's vision.

2. Beta-irradiation may be used when medication alone proves insufficient.

3. Excision of a superficial layer from the affected area may restore vision in opacified eyes. This is called superficial keratectomy.

However, the recurrence rate postoperatively is high and this method remains only as a last resort.

The main side-effect of the prolonged topical corticosteroid therapy is an adverse effect on corneal wound healing. Microscopic wounds of the superficial layer of the cornea occur very commonly and heal rapidly in a normal eye. Under the influence of continuing corticosteroid therapy, minor wounds may progress and can even cause rupture of the eye. The hallmark of such a wound is pain. Therefore, should a dog on corticosteroid therapy show signs of pain, as holding the eye shut or pawing at the eye, it is imperative that the medication is discontinued and a veterinarian consulted

If you have any questions about Pannus (Chronis superficial keratitis), please do not hesitate to call us at Eye Care for Animals.