Only a small percentage of people with hyperthyroidism develop exophthalmos.
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The thyroid gland is part of the endocrine system, a complex network of hormone-producing organs that controls many basic body processes. Thyroid hormone controls the rate at which your cells process and use nutrients to produce energy. When your thyroid is overactive in hyperthyroidism, it can have major effects on your body. One of its effects is a condition called exophthalmos, a problem that affects the eyes.
In hyperthyroidism, the thyroid gland makes too much thyroid hormone, which causes cells to increase their rate of activity. Hyperthyroidism has several causes, including an irritation or inflammation of the thyroid causing hormone to leak from the gland, or consuming too much iodine, which can stimulate high hormone production. The most common cause of hyperthyroidism is Graves disease. In this disorder, the immune system erroneously makes a substance called an antibody that attaches to thyroid cells, causing them to make too much hormone.
Graves disease is 7 to 10 times more likely to develop in women, especially those between 20 and 50 years old. Each year, about 1 woman in 2,000 develops the disorder. Symptoms of Graves disease and other forms of hyperthyroidism include nervousness, an intolerance of heat, tremors, irregular heartbeat and weight loss. People with Graves disease sometimes develop eye irritation or dryness. In about 2 to 5 percent of cases, eye problems can be severe and may include exophthalmos.
Exophthalmos is a condition whose name comes from the Greek word for bulging eye. Technically, it is also called proptosis and orbitopathy, referring to a problem in the orbit, a cup-shaped area in the skull that contains the eyeball. Although other conditions, such as trauma or a tumor behind the eye, can cause exophthalmos, the most common cause is hyperthyroidism, usually from Graves disease, which affects both eyes.
In exophthalmos, changes in the connective tissue in the orbit, behind the eye itself, cause the tissue to swell and push the eyeball forward. If exophthalmos is severe and goes untreated, a person might be unable to close his eyelids, even during sleep. This can cause the cornea to become dry, irritated and potentially damaged. In extreme cases, exophthalmos might put enough pressure on the optic nerve, which is behind the eye, to cause vision problems.
In people with hyperthyroidism caused by Graves disease, about 50 percent develop eye problems, but these are severe in only 3 to 5 percent of people. Severe eye problems, such as exophthalmos, develop 4 times more often in men with Graves disease than in women, even though Graves disease itself is more common in women than men. The reason for the increased risk of eye problems in men is not understood.
Cigarette smoking also raises the risk of hyperthyroidism-associated eye disorders, according to a study published in October 2002 in the journal "Thyroid." The authors also found that when eye problems develop in smokers, they tend to be more severe than in nonsmokers. How smoking contributes to eye problems such as exophthalmos in hyperthyroidism is not known, but may be related to changes in the immune system caused by compounds in cigarettes or cigarette smoke.
Treatment of hyperthyroidism and associated eye problems, such as exophthalmos, depend partly on the severity of the condition. A doctor may recommend taking anti-thyroid medications, radioiodine therapy to stop thyroid function partially, or thyroid surgery in certain cases. Often, once treatment is started, eye problems get better over time.
When exophthalmos is severe, especially if it causes vision problems, the doctor may recommend a surgical procedure called orbital decompression, which can increase the space behind the eye. This usually relieves pressure and allows the eye to move back into a normal position. If you have or suspect you have hyperthyroidism, discuss the disorder with your family doctor or a specialist in endocrinology, who can advise you on the best action for your situation.