Graves' Disease: This is the most common cause of bilateral exophthalmos, resulting from autoimmune thyroid disease leading to inflammation and swelling of the tissues around the eye, including the eyelids, eye socket, and lacrimal gland.

Orbital Cellulitis: An infection of the tissues surrounding the eye, which can cause swelling and protrusion of the eyeball.
Thyroid Ophthalmopathy (not limited to Graves' Disease): Other thyroid conditions can also lead to exophthalmos, though Graves' disease is the most common.
Orbital Tumors: Tumors behind or around the eye can push the eyeball forward, causing exophthalmos.

Cavernous Sinus Thrombosis: A blood clot in the cavernous sinus, a group of veins located behind the eye, can lead to exophthalmos and is life-threatening if not promptly treated.
Meningioma: A type of brain tumor that can grow near the optic nerve and cause exophthalmos, among other symptoms.
Carotid-Cavernous Fistula: An abnormal connection between the carotid artery and cavernous sinus, leading to increased pressure and potential exophthalmos.

Neurofibromatosis Type 1: A genetic disorder that can cause tumors to grow along nerves, including those behind the eye, leading to exophthalmos.
Sarcoidosis: A condition in which inflammatory cells grow in different parts of the body, including the eyes, potentially causing exophthalmos.
Wegener's Granulomatosis (Granulomatosis with Polyangiitis): A rare autoimmune disorder that can cause inflammation in various parts of the body, including the eyes, leading to exophthalmos.