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.

Exophthalmos has endocrine causes. 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.

Many patients with exophthalmos have a history of endocrine abnormalities, including thyroid related disease or “thyrotoxic activity”. Other endocrine related causes of exophthalmos include infection and “IgG4-related disease”. The most common cause of exophthalmos in adults is eye disease associated with a dysfunctioning thyroid gland. Exophthalmos in children is possible and most likely caused by tumors or cancers like leukemia. In rare cases, exophthalmos can occur in patients with normal thyroid function or underactive thyroid function.

The thyroid gland is stimulated by thyroid-stimulating hormone (TSH). The majority of patients with Grave’s disease have antibodies called thyroid-stimulating antibodies, which are immune to the thyroid stimulating hormone. The thyroid stimulating hormone has some receptors in the fat cells around the eyeballs. The immune system attacks the fatty tissues, as well as other tissues around the eyes, causing them to stick out from the sockets. There is something called exophthalmos-producing substance, which competes with thyroid stimulating hormone receptors. The affinity of the exophthalmos-producing substance is strengthened if there is also "ophthalmologic immunoglobulins".

Exophthalmos can also happen from something that pushes the eye toward the front of the socket. Some examples include blood clots, tumors, infection, or trauma..

According to the NCBI, the following conditions feature exophthalmos:

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.