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[ChinitoDr]

Exophthalmos is an abnormal bulging of one or both eyes.

Many conditions can cause exophthalmos. In some types of thyroid disease, especially Graves' disease (see Thyroid Gland Disorders: Causes), the tissues in the orbit swell and accumulate certain types of cells (such as lymphocytes), which push the eyeball forward. Exophthalmos can develop rapidly from bleeding behind the eye or from inflammation in the orbit. Tumors, either cancerous or noncancerous, can form in the orbit behind the eyeball and push it forward. An unusual noncancerous accumulation of inflammatory and fibrous tissue (pseudotumor) may produce exophthalmos with pain and swelling. Cavernous sinus thrombosis causes swelling because blood in the veins cannot exit the eye. Abnormal connections between the arteries and veins (arteriovenous malformations) behind the eye may produce a pulsating exophthalmos, in which the eye bulges forward and pulses along with the heartbeat.

The protruding eye is less protected by the eyelids, and the cornea may become too dry. As a result, corneal ulcers may form, which can become infected. Prolonged exophthalmos can impair vision because the optic nerve is stretched. The increased pressure within the orbit may also result in compression of the optic nerve, which can also impair vision.

Diagnosis and Treatment
All people with protruding eyes do not necessarily have exophthalmos. Some people simply have prominent eyes with more white showing than normal. The extent of the protrusion can be measured with an ordinary ruler or with an instrument called an exophthalmometer. Further diagnostic tests may include computed tomography (CT) and thyroid function tests.

The treatment depends on the cause. If the problem is an abnormal connection between arteries and veins, surgery may be needed to close off certain blood vessels. Thyroid disease that is severe enough to cause exophthalmos may need to be treated. But it is unclear if treating the thyroid condition actually improves bulging of the eyes. Treatment of exophthalmos includes eyeshades and eye drops if symptoms are mild, or corticosteroids, radiation therapy, or surgery if the condition is more severe. Treatment of bleeding or inflammation involves treating the underlying disorder (see Eye Socket Disorders: Inflammation). Tumors (depending on type) are treated with chemotherapy, radiation therapy, or surgery. Corticosteroids may help the inflammation caused by a pseudotumor

credits:http://www.merck.com/mmhe/sec20/ch236/ch236f.html