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Pannus is an old term describing a membrane that covers the cornea as a result of long term corneal inflammation. More recently the syndrome is referred to as Chronic Superficial Keratitis (CSK); ie., long term inflammation of the cornea. Pannus has no known cause. However, it is important to recognize that the cornea is very limited in its ability to respond to injury and this may play a role in the development of pannus. Understanding the anatomy of the cornea is helpful in understanding the syndrome of pannus. The cornea is the clear part of the globe that covers the iris and pupil. It extends outward with a convex exterior curvature from the sclera or white of the eye. The healthy cornea is clear and has no blood vessels within itself. The cornea receives all of its nutrients from a perpetual bath of tears. Tears are essential to the normal function and health of the cornea. The cornea consists of 3 layers: outer (epithelium), inner (endothelium), and a middle layer (stroma). The cornea remains transparent as long as the protein of the stroma is perfectly aligned. Anything that upsets this alignment interferes with corneal transparency. The epithelium and endothelium act as barriers for the stroma and help maintain the precise environment for transparency. Pannus is a membrane of small blood vessels and inflammatory cells that cover the epithelium of the cornea thus, obstructing vision much like a window shade. Their is a strong breed predisposition for German Shepherds as well as crosses of Shepherds. Additionally, pannus is more frequent in Border Collies, Huskies, Tervuren and Australian Shepherds. The syndrome is also more common in higher altitudes where there is more exposure to uv light. Most dogs are presented in their middle years however, the syndrome can occur in young and old. Because the disease responds to Corticosteroids, it is strongly suspected to be an immune related disease. These are diseases that for reasons that are not clear, the individual¹s immune system responds to a tissue as if it is a foreign substance and is not native to the body. In addition, microscopic analysis supports this immune mediated concept of the disease. Signs of the disease include bilateral appearances of corneal pigment and small blood vessels spreading out over the cornea. Uncommonly, the pannus can erode the epithelium and alter the transparency of the stroma. A diagnosis ruling out other cause of keratitis is fundamental. Dry eye syndrome (loss of tear production) and congenital eyelid deformities are important differential diagnoses to consider. Treatment is mostly medical, although there are several surgical procedures used in advanced non responding cases. These include irradiation of the area and the use of liquid nitrogen. Medically, topical and injectable steroids are commonly employed. Prednisolone acetate 1% suspension and dexamethasone 0.1% suspension are the two main topical corticosteroids used. Injections in to the conjunctiva are also frequently used. These include long acting steroids that give a response of several weeks. Recently, the use of cyclosporin A has become popular now that the drug is commercially available as an ophthalmic. Cyclosporin may improve the response significantly. In some cases the use of topical drugs can be decreased in frequency as the pannus comes under control. Rarely does the problem completely resolve and for the vast majority of cases it requires lifelong therapy. Occasionally, a pannus will not respond. Fortunately, the disease is rarely painful. At worst it obstructs vision and may cause blindness. In the future, corneal Epidermal Growth Factors and Transforming Growth Factors may offer additional treatment as these drugs enter the commercial market.