Sclera

The sclera consists of three layers: the lamina fusca, which communicates with the outer choroid; the sclera proper, which is composed of connective tissue; and the episclera, which consists of loose connective tissue and is highly vascular (Samuelson, 2007).

Scleral inflammation can be primary or secondary to other ocular inflammatory diseases. Primary canine episcleritis has been characterized immunohistochemically as a mixture of T and B lymphocytes and CD18⁺ histiocytic cells (Breaux et al., 2007). Cytologically, there will be a mixed inflammatory population predominated by small lymphocytes with high numbers of vacuolated macrophages. Low numbers of neutrophils can be observed.