Bulging eyes are not a disease in itself but rather a symptom seen in several different diseases and disorders. Anterior protrusion of the eyes from their orbits is scientifically called exophthalmosis or proptosis and it can be unilateral, affecting just one eye, or bilateral, when it affects both eyes. The onset of bulging eyes can be slow and gradual or rather sudden, and the extent to which the eye protrudes from the orbit is measured using an instrument called exophtamometer.
Bulging eyes can be caused by an injury or trauma, as a direct result of swelling of the tissue. This condition must be treated immediately, because if it is neglected it may lead to damage to the eyelids, that eventually may fail to close during sleep, and this, in turn, can cause damage to the cornea.
One of the major causes of bulging eyes is Graves’ disease, but it can be the symptom of other diseases as well.
Graves’ disease is an autoimmune disorder in which the thyroid gland is enlarged, resulting in overproduction of thyroid hormones. The systemic changes that occur due to this disorder are caused by the antibodies that activate the THS receptor and stimulate the production and secretion of the thyroid hormones. Those antibodies in the blood target the fibroblasts in the eye muscle, fat cells and muscles expand and become inflamed. The veins, that would normally drain fluid, are compressed and unable to do so, causing edema and protrusion of the eye out of the orbit.
Abnormalities in the connective tissue in the eye and around the extraocular muscles can be observed using a CT scan or an MRI. Bulging eyes are not the only symptom of Graves’ disease, and other symptoms are similar to those caused by hyperthyroidism.
Protrusion or bulging eyes are most commonly a symptom of Graves’ disease, but there are many other medical reasons for this condition. It can result from diseases directly affecting the eyes. It can also be a sign of a tumor, especially if the protrusion is unilateral. Eye cancer is relatively rare and it's most common form is retinoblastoma, with melanoma being the second most common form.
Glaucoma, a disorder characterized by increased pressure inside the eyeball, is another possible cause of bulging eyes.
Physical injury, trauma, bleeding or infection call all cause protrusion of the eye, although it does not happen very often and it is usually limited only to the affected eye.
Other diseases and conditions that may cause bulging eyes, although it rarely happens, include leukemia, orbital cellulitis, meningioma, hemangioma, Duane syndrome, carotid cavernous fistula and dacryoadenitis and high altitude cerebral edema.