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In corneal pannus, a fibrous tissue with a significant vascular component is seen between the epithelium and Bowman's layer; this is called “subepithelial fibrovascular pannus.” There are two types of corneal pannus: inflammatory pannus and degenerative pannus. Inflammatory pannus is associated with prominent leukocytic infiltration and includes polymorphonuclear leukocytes in the active stages. However, by the time the pathologist detects the inflammatory pannus, it is commonly constituted by overwhelming numbers of lymphocytes and plasma cells. Frequently, the Bowman's layer is disrupted, and the vessels wander haphazardly through the anterior stroma. In degenerative pannus, there are fewer inflammatory cells. The vascular component has never been prominent and is liable to regress, leaving a hyalinized, relatively acellular layer of fibrous tissue. This type of pannus is especially common in conditions that give rise to chronic epithelial edema, such as glaucoma.

Stromal NV …