How Does Thyroid Eye Disease Affect The Thyroid?
Thyroid eye disease (TED) is a rare autoimmune disease. Autoimmune diseases occur when the body’s immune system cannot tell the difference between invaders (viruses, fungi, or bacteria) and healthy cells. Because it cannot tell the difference, the body begins to attack and damage healthy cells.1,2
Antibodies are proteins your body makes to kill germs. In TED, harmful antibodies attack various parts of the body, including the tissues around the eyes. This results in inflammation and damage to the muscles, connective tissues, and fat around the eyes. Injury and inflammation are progressive, with an active and inactive phase.1,3
Knowing how TED impacts the thyroid gland, the resulting symptoms, and various thyroid conditions help you to better understand the overall impact of TED.
What is the thyroid gland?
Your thyroid is a gland located at the bottom of your neck, just below your Adam’s apple. The thyroid releases thyroid hormones, which play an important role in nearly every body function. The main job of the thyroid gland is metabolism, or the speed at which your cells work.3,4
A small gland in your brain called the pituitary gland makes and releases a hormone called thyroid-stimulating hormone (TSH). TSH tells the thyroid how much thyroid hormones (known as T3 and T4) to make.5,6
Your body likes to be in a state of balance. If T3 and T4 levels drop too low, the pituitary gland makes and secretes more TSH. This causes the thyroid to make more thyroid hormones.5,6
Your thyroid and TED
Too much of T3, T4, or both results in an overactive thyroid (hyperthyroidism). A protein connected to thyroid hormone is known as insulin-like growth factor 1 receptor (IGF-1R). Too much thyroid hormone "turns on'' the IGF-1R protein. This leads to the growth of muscle, fat, and connective tissue cells.3
Your eyes have muscle, fat, and connective tissue that are impacted by too much thyroid hormone and IGF-1R. This causes symptoms of TED, including:3
- Bulging of the eyes
- Puffy eyelids
- Red, irritated, and painful eyes
- Dry, gritty eyes
- Watery eyes
- Blurred vision
- Problems seeing different colors
- Double vision
Thyroid function and TED
Most people with TED have an overactive thyroid gland (hyperthyroidism). Some people with TED may have an underactive thyroid (hypothyroidism). TED can also occur in those with a normal-functioning thyroid, but this only happens in about 1 out of every 100 people with TED.4
Like TED, Graves’ disease is an autoimmune disease. However, 1 disease does not cause the other. Graves’ disease causes an overactive thyroid (hyperthyroidism) and affects about 1 out of every 200 people in the United States.5,6
In Graves’ disease, the body makes an abnormal antibody called thyroid-stimulating immunoglobulin (TSI). TSI mimics TSH and tricks the body into thinking it needs more thyroid hormone. This causes the body to make too much T3 and T4, leading to an overactive thyroid and increased metabolism.5,6
Because TSI is a harmful antibody, it begins to attack normal cells and proteins in the thyroid. Doctors think the proteins around the eye are similar to those in the thyroid. This explains why TSI also attacks the tissues around the eye. Damage to the tissue around the eyes leads to the symptoms of TED.1,3,6
Up to half of those with Graves’ disease develop TED. Despite this link, TED and Graves’ disease are different conditions requiring unique treatment.7
About 1 in 10 people with TED have lower thyroid function (hypothyroidism). The most common cause of hypothyroidism in the United States is Hashimoto’s thyroiditis. Like Graves’ disease, Hashimoto’s thyroiditis has harmful antibodies that attack the thyroid.3
When the antibodies attack the thyroid in this condition, inflammation results and causes reduced thyroid function. Hashimoto’s is most common in middle-aged women but can impact men and women at any age. Children may also be affected.8
TED is not simply an eye disease. The impact on your thyroid varies from person to person. You might even have a normal-functioning thyroid gland and have TED. Because of these differences, getting the care you need is essential. Talk to your doctor about your symptoms in order to get the right treatment for TED.