What causes thyroid eye disease (TED)?

Thyroid eye disease (TED) is a condition that most often occurs alongside a thyroid disorder called Graves’ disease. Both Graves’ disease and TED are autoimmune disorders, conditions where the body’s immune system attacks healthy tissues.

With Graves’ disease, the autoimmune attack is directed at the thyroid gland and causes an overproduction of thyroid hormone (and the many symptoms that can result from an overproduction of thyroid hormone).

With TED, the autoimmune attack is directed at the tissues that surround the eyes—muscles, fatty tissue, and other soft tissues that form supportive structures that help keep the eyes in place and correctly aligned.

TED causes the eyes to bulge or protrude forward. This changes the appearance of the face, which can cause significant mental and emotional distress. It can also cause dry eye, irritation, pain, and discomfort. In some cases, TED causes vision problems, such as double vision.

What causes TED?

The causes of Graves’ disease and TED are not well understood—and the causes of autoimmune disorders in general are not well understood. Research has identified some of the factors and mechanisms that are at work in the body when a person has Graves’ disease and TED.

Genetics and environmental factors

Like many autoimmune disorders, Graves’ disease and TED are believed to be caused by a combination of genetic and environmental factors. This means a person has specific gene mutations that make them more susceptible to having these conditions, and the disease becomes active when a person is exposed to an environmental trigger.

Several genes associated with Graves’ disease have been identified. Tobacco smoke is the most well-known environmental risk factor for TED. It increases the risk of TED and having more severe TED symptoms. Smoking also lowers the response to certain treatments for TED. Quitting smoking and avoiding secondhand smoke are strongly advised for anyone with these conditions.

Inflammation

Like many autoimmune disorders, TED causes inflammation. Inflammation is a response by the body’s immune system. Under normal circumstances, inflammation protects the body, flooding an area of injury or infection with immune cells that destroy and remove damaged or diseased cells.

Essential to this process are antibodies, proteins that attach to damaged and diseased cells and direct the immune system where to attack. If you have ever had the area around an abrasion become swollen or felt your sinuses become congested when you have a cold, you’ve felt inflammation at work, doing what it is intended to do.

Autoantibodies

With some autoimmune disorders, the body produces “autoantibodies.” These are antibodies that attach to one’s own healthy cells—and direct the immune system to attack those healthy cells. When a person has Graves’ disease, the body produces an autoantibody called thyroid-stimulating hormone (TSH) receptor antibody. This antibody attaches to cells on the thyroid gland in the throat. In some cases, it also attaches to tissues that surround the eyes and causes TED.

Your best source of information

It’s important to keep in mind that the above is a simplified explanation of a very complex disease. It’s also important to remember that there are still many unanswered questions about Graves’ disease and TED.

When you are living with a chronic condition like Graves’ disease and/or TED, having a basic understanding like this can help you prepare for conversations with your healthcare team, who will be your best source of information on your diagnosis, treatment options, and what you can do to stay healthy while living with these conditions.