Thyroid Eye Disease (TED), sometimes called Graves’ ophthalmopathy or Graves’ Eye Disease, is an autoimmune disease in which the immune system causes inflammation and swelling and stimulates the production of muscle tissue and fat behind the eye. The overactive thyroid gland (hyperthyroidism) is usually caused by Graves’ disease. Up to one-half of people with Graves’ disease develop thyroid eye disease. In some people, thyroid eye disease can occur with normal levels of thyroid hormones (euthyroid) or low levels of thyroid hormones (hypothyroidism). Thyroid eye disease may occur in patients who already know they have thyroid disease, or it may be the first sign of Graves’ disease. While TED often occurs in people living with hyperthyroidism or Graves’ disease, it is a distinct disease and treating hyperthyroidism may not resolve the eye symptoms and signs.