Fibrous histiocytoma involves most commonly:
Eyelid
Epibular
Intraocular
Orbit
Fibrous histiocytoma is the most common primary mesenchymal orbital tumor in adults. 
It may involve ocular structures such as the orbit, lids, conjunctiva, and ocular limbus. 
Most fibrous histiocytomas are benign, but some are locally aggressive and malignant.