Thyroid eye disease (TED) is an autoimmune condition in which the body’s immune system attacks the tissues behind and around the eyes, causing them to swell, push forward, and sometimes lose function. It affects roughly 13 to 24 people per 100,000 in the United States and is most closely linked to Graves’ disease, though it can occasionally occur with other thyroid conditions or even normal thyroid function.
What Happens Inside the Eye Socket
The problem starts with a case of mistaken identity. In Graves’ disease, the immune system produces antibodies that latch onto receptors on thyroid cells, which is what causes the thyroid to overproduce hormones. Those same receptors also exist on cells called orbital fibroblasts, which live in the fat and muscle tissue behind your eyes. When autoantibodies bind to these fibroblasts, the cells respond as if they’ve been switched on: they release inflammatory signals that recruit more immune cells into the orbit, and they begin to change form.
Some fibroblasts transform into cells that produce scar tissue and a gel-like substance called hyaluronic acid, which absorbs water and causes the muscles behind the eye to thicken. Others turn into fat cells, adding volume behind the eyeball. The combined effect of extra fat, swollen muscles, and accumulated fluid is what pushes the eye forward and restricts its movement. Over time, if inflammation goes unchecked, scarring can make these changes permanent.
Symptoms From Earliest to Most Severe
TED tends to announce itself gradually. The earliest signs are dry eyes and persistent redness, often dismissed as allergies or fatigue. Next comes eyelid retraction, the wide-eyed “stare” that results from the upper lid pulling back to expose white above or below the iris. As swelling increases behind the eye, the eyeball itself starts to bulge forward, a change called proptosis.
More advanced disease restricts how well the eyes can move, which leads to double vision (diplopia). Some people find they can no longer fully close their eyelids, leaving the surface of the eye exposed and vulnerable to drying and ulceration. In the most severe cases, the swollen tissue compresses the optic nerve at the back of the orbit, causing blurred vision, faded color perception, and, without treatment, permanent vision loss. Pain or pressure behind the eyes, particularly when looking up or to the side, is common throughout the course of the disease.
The Active and Stable Phases
TED moves through two distinct phases. In the active phase, inflammation is ongoing: redness, swelling, pain, and bulging eyes tend to worsen over time. This phase typically lasts between six months and three years. During this window, treatment focuses on calming the immune response before permanent damage sets in.
Once the inflammation burns out, the disease enters the inactive (or stable) phase. Symptoms stop getting worse, but the structural changes left behind often remain. Scar tissue locks the muscles and fat in their swollen positions, so proptosis, eyelid retraction, and double vision can persist long after inflammation has resolved. This is why early treatment during the active phase matters so much.
Doctors use a scoring system called the Clinical Activity Score to determine which phase you’re in. It assigns one point each for symptoms like eye pain at rest, pain with eye movement, eyelid swelling, eyelid redness, swelling of the white part of the eye, and measurable worsening of proptosis or eye movement over one to three months. A higher score signals active disease that may respond to anti-inflammatory treatment.
Smoking and Other Risk Factors
Smoking is the single most significant modifiable risk factor. Compared to nonsmokers, people who smoke are roughly 7.7 times more likely to develop TED. Among patients who already have Graves’ disease, smoking doubles the incidence of eye bulging and triples the rate of double vision. It also makes treatment less effective: smokers respond more poorly to steroids and radiation therapy and are more likely to need surgery. If you smoke and have been diagnosed with Graves’ disease or TED, quitting is the most impactful thing you can do to protect your eyes.
Other risk factors include being female (TED is significantly more common in women), having poorly controlled thyroid hormone levels in either direction, and undergoing radioactive iodine therapy for hyperthyroidism, which can sometimes trigger or worsen eye disease. Genetic predisposition plays a role as well, though no single gene has been identified as the cause.
How TED Is Treated
Treatment depends on severity and disease phase. For mild active disease, a daily supplement of 200 micrograms of selenium taken over six months has been shown in a randomized trial to reduce severity during the inflammatory phase. Lubricating eye drops, prism glasses for mild double vision, and sunglasses to manage light sensitivity are standard supportive measures.
Moderate to severe active disease is typically treated with high-dose steroids delivered intravenously, which tamp down inflammation. A newer option targets the underlying immune mechanism more precisely. This treatment, a biologic drug that blocks the receptor on orbital fibroblasts responsible for much of the swelling, reduced eye bulging by an average of about 2.4 millimeters over 24 weeks in clinical trials. Around 62% of patients treated with it achieved a meaningful reduction in proptosis, compared to 25% on placebo.
Surgery is reserved for the stable phase once inflammation has settled, with one important exception: if the optic nerve is being compressed and vision is threatened, emergency orbital decompression can be performed during active disease. For non-urgent cases, surgery addresses the cosmetic and functional changes left behind. Orbital decompression creates more room in the eye socket by removing small amounts of bone or fat. Strabismus surgery realigns the eye muscles to correct double vision. Eyelid surgery corrects retraction so the lids close properly. These procedures are typically staged in that specific order, each building on the results of the one before.
Conditions That Can Look Similar
Not every case of bulging or swollen eyes is TED. Bilateral proptosis developing slowly and painlessly is the classic pattern that points toward thyroid-related disease, but other conditions can mimic parts of the picture. Orbital pseudotumor, an inflammatory condition of unknown cause, produces lid swelling, redness, pain, and restricted eye movement. Certain autoimmune blood vessel diseases can cause bilateral proptosis with painful, limited eye movements. Orbital tumors tend to cause one-sided bulging. Infections of the eye socket come on quickly with fever and visible illness.
A key distinction is timing and symmetry. TED usually develops gradually over weeks to months, affects both eyes (though sometimes unevenly), and occurs alongside a history of thyroid problems. If one eye bulges suddenly or you feel generally unwell, the cause is more likely something other than TED and warrants urgent evaluation. Blood tests for thyroid function and thyroid antibodies, combined with imaging of the eye sockets, typically clarify the diagnosis.