 On histological examination, there is an infiltration of the orbital connective tissue by lymphocytes, plasmocytes, and mastocytes.The inflammation results in a deposition of collagen and glycosaminoglycans in the muscles, which leads to subsequent enlargement and fibrosis.There is also an induction of the lipogenesis by fibroblasts and preadipocytes, which causes enlargement of the orbital fat and extra-ocular muscle compartments.