Thyroid eye disease: Retro-orbital fat and muscle

Both the retro-orbital fat and muscles are involved in the development of thyroid eye disease. Cytokine released from fibroblast and pre-adipocytes accentuate the secretion of hyaluronic acid-like molecules, which increase the osmotic pressure in the tissues causing fluid accumulation and, in particular, disruption of the muscle bundles. This figure shows the marked swelling of the retro-orbital muscles, often well visualized on MRI or CT scanning in such patients. The consequence of retro-orbital swelling is proptosis (exophthalmos), not well illustrated here, since this may depend on both the anatomy of the orbit and the degree of swelling.