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 individual s 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.