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Pannus

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.