Exophthalmos (also called exophthalmus, exophthalmia, proptosis, or exorbitism) is a bulging of the eye anteriorly out of the orbit. Exophthalmos can be either bilateral (as is often seen in Graves' disease) or unilateral (as is often seen in an orbital tumor). Complete or partial dislocation from the orbit is also possible from trauma or swelling of surrounding tissue resulting from trauma. In the case of Graves' disease, the displacement of the eye results from abnormal connective tissue deposition in the orbit and extraocular muscles, which can be visualized by CT or MRI. If left untreated, exophthalmos can cause the eyelids to fail to close during sleep, leading to corneal dryness and damage. Another possible complication is a form of redness or irritation called superior limbic keratoconjunctivitis, in which the area above the cornea becomes inflamed as a result of increased friction when blinking. The process that is causing the displacement of the eye may also compress the optic nerve or ophthalmic artery, and lead to blindness. Causes Inflammatory/Infection: Graves' ophthalmopathy due to Graves' disease, usually causes bilateral proptosis. Orbital cellulitis – often with unilateral proptosis, severe redness, and moderate to severe pain, sinusitis and an elevated white blood cell count. Dacryoadenitis Erdheim–Chester disease Mucormycosis Orbital pseudotumor – presents with acute, usually unilateral proptosis with severe pain. High-altitude cerebral edema Granulomatosis with polyangiitis Neoplastic: Leukemias Meningioma, (of sphenoid wing) Nasopharyngeal angiofibroma Hand–Schüller–Christian disease Hemangioma, cavernous Cystic: Dermoid cyst Vascular: Carotid-cavernous fistula Aortic insufficiency: manifests as a pulsatile pseudoproptosis, described by British cardiothoracic surgeon Hutan Ashrafian in 2006 Others: Orbital fracture: apex, floor, medial wall, zygomatic Retrobulbar hemorrhage: trauma to the orbit can lead to bleeding behind the eye. The hemorrhage has nowhere to escape and the increased pressure pushes the eye out of the socket, leading to proptosis and can also cause blindness if not treated promptly. Cushing's syndrome (due to fat in the orbital cave) Some forms of craniosynostosis: Crouzon syndrome Pfeiffer syndrome Pansynostosis Anatomy Proptosis is the anterior displacement of the eye from the orbit. Since the orbit is closed off posteriorly, medially and laterally, any enlargement of structures located within will cause the anterior displacement of the eye. Swelling or enlargement of the lacrimal gland causes inferior medial and anterior dislocation of the eye. This is because the lacrimal glands are located superiorly and laterally in the orbit. Diagnosis Measurement Measurement of the degree of exophthalmos is performed