TED stands for thyroid eye disease, an autoimmune condition in which the body’s immune system attacks the tissues behind and around the eyes, causing swelling, bulging, pain, and sometimes vision loss. Though it shares its root cause with thyroid disorders like Graves’ disease, TED is its own distinct condition that can appear even when thyroid hormone levels are normal. About five people per 100,000 develop it each year, and it disproportionately affects women at roughly a four-to-one ratio compared to men.
Who Gets TED
A nationwide study in Denmark tracked every new TED diagnosis over 19 years and identified more than 4,100 cases. Women accounted for about 81% of diagnoses, with an incidence of 8.0 per 100,000 person-years versus 1.9 for men. The average age at onset was around 51, though TED can appear at any age.1JAMA Ophthalmology. Nationwide Incidence of Thyroid Eye Disease and Cumulative Incidence of Strabismus and Surgical Interventions in Denmark
Most people diagnosed with TED are hyperthyroid at the time, which makes sense given the Graves’ disease connection. In that same Danish cohort, about 74% were hyperthyroid, roughly 12% were hypothyroid, and about 15% had normal thyroid function when their eye disease was first identified. That last group is worth noting because many people assume you need an overactive thyroid to develop TED. You do not. Among those who were euthyroid (normal thyroid levels) at diagnosis, about 41% went on to need antithyroid medication within four years, suggesting the thyroid dysfunction simply had not surfaced yet.2JAMA Ophthalmology. Nationwide Incidence of Thyroid Eye Disease and Cumulative Incidence of Strabismus and Surgical Interventions in Denmark
TED also shows some sex-linked differences in how it presents. One study found that nearly all hyperthyroid women with TED had symmetric disease, meaning both eyes were affected roughly equally, while men and patients with other thyroid states were more likely to have one eye worse than the other.3PubMed Central. The relationship between sex and symmetry in thyroid eye disease
What Is Happening Behind the Eyes
The core problem in TED involves a misdirected immune attack on cells called orbital fibroblasts, which live in the fat and connective tissue cushioning the eyeball. In people with TED, these fibroblasts overexpress a receptor called the IGF-1 receptor. This receptor interacts with the TSH receptor, the same protein that thyroid-stimulating antibodies latch onto in Graves’ disease, and the two receptors amplify each other’s signals.4PubMed Central. Mechanisms in Thyroid Eye Disease: The TSH Receptor Interacts Directly With the IGF-1 Receptor The result is a cascade of inflammation and tissue expansion inside the bony eye socket, a space that has very little room to spare.
One of the key downstream effects is increased adipogenesis, meaning the orbital fibroblasts start turning into fat cells at a much higher rate than normal. A transcriptomic study comparing orbital fat from TED patients to healthy controls found a marked increase in fibroblasts transitioning to fat cells, along with widespread changes in immune cell composition. The IGF-1R signaling pathway showed significant abnormalities, and blocking that pathway with a drug called linsitinib reduced the abnormal fat production in lab settings.5The Journal of Clinical Investigation. Transcriptomic profiling of thyroid eye disease orbital fat demonstrates differences in adipogenicity and IGF-1R pathway
The swelling of fat and muscle tissue in the eye socket has nowhere to go, which pushes the eyeball forward (proptosis) and compresses the muscles that control eye movement and, in severe cases, the optic nerve itself.
Symptoms and How TED Progresses
TED can range from a cosmetic nuisance to a sight-threatening emergency. Roughly 60% of patients develop relatively mild symptoms: puffy eyelids, a feeling of grittiness or dryness, mild bulging of the eyes, and eyelid retraction that creates a wide-eyed or staring appearance. The remaining patients experience more serious involvement, including significant swelling of the eye muscles, restricted eye movement, double vision, and in the worst cases, compression of the optic nerve.6PubMed. Extrathyroidal Manifestations of Thyroid Disease: Graves Eye Disease
The disease typically moves through two phases. The active phase involves worsening inflammation, and it usually lasts anywhere from several months to about two years. During this period, the eyes may become progressively more swollen, red, and painful. After the active phase comes the inactive or fibrotic phase, where inflammation dies down but the tissue changes that occurred (expanded fat, scarred muscles) become permanent unless treated. Doctors gauge which phase a patient is in using a tool called the Clinical Activity Score, which tallies signs like spontaneous eye pain, redness, and swelling to produce a number that helps guide treatment decisions.7PubMed. Updates on Treatment in Thyroid Eye Disease for the Neurologist
Double vision (diplopia) and optic nerve compression (dysthyroid optic neuropathy) are the most functionally disabling complications.8PubMed Central. Optic neuropathy and diplopia from thyroid eye disease: update on pathophysiology and treatment Dry eye is also common, caused both by immune cells infiltrating the tear glands and by eyelid retraction that leaves the surface of the eye exposed.9The Journal of Clinical Endocrinology & Metabolism. Approach to the patient: therapeutic mitigation of lacrimal manifestations in thyroid eye disease
Why Smoking Makes TED Worse
If there is one modifiable risk factor that stands out for TED, it is cigarette smoking. A systematic review found strong evidence for a causal link between smoking and both the development and progression of TED. Current smokers were more likely to develop the condition in the first place, and once they had it, they were more likely to see it worsen and respond poorly to treatment.10PubMed. Cigarette smoking and thyroid eye disease: a systematic review
The practical difference is substantial. In a retrospective study of patients treated with teprotumumab (the main targeted drug for TED), smokers saw far less improvement in eye bulging than nonsmokers. Proptosis in nonsmokers dropped by about 4 mm per eye on average, while smokers saw reductions of only about 1 to 2 mm.11PubMed Central. Effects of Smoking on Outcomes of Thyroid Eye Disease Treated with Teprotumumab: A Retrospective Cohort Study Mechanistic research suggests that cigarette smoke activates a signaling pathway called RAGE, which drives inflammation in the orbital tissues and worsens the disease independent of the underlying autoimmune process.12PubMed. Cigarette Smoking Drives Thyroid Eye Disease Progression via RAGE Signaling Activation
For anyone with Graves’ disease or early TED, quitting smoking is the single most effective thing they can do to improve their outlook. No medication fully compensates for continuing to smoke.
Radioactive Iodine and TED Flares
Radioactive iodine (RAI) is a common treatment for Graves’ hyperthyroidism, but it carries a specific risk for the eyes. The destruction of thyroid tissue releases a flood of thyroid antigens that can amplify the immune response in the orbit. In a classic trial, patients who already had some eye involvement before RAI therapy saw their eye disease worsen more than half the time when they did not receive protective corticosteroids. In contrast, those given systemic corticosteroids alongside RAI saw improvement or no change.13PubMed. Use of corticosteroids to prevent progression of Graves’ ophthalmopathy after radioiodine therapy for hyperthyroidism This is why many endocrinologists now prescribe a short course of steroids to cover RAI treatment in patients who show any signs of TED.
How TED Is Diagnosed
Diagnosis is usually clinical, based on the combination of thyroid disease and characteristic eye findings like proptosis, eyelid retraction, and restricted eye movement. Blood tests for thyroid-stimulating immunoglobulins (TSI) help confirm the autoimmune basis. When the diagnosis is uncertain or when doctors need to assess disease activity before choosing treatment, MRI of the orbits can be helpful. T2-weighted MRI sequences can detect inflammation in the eye muscles, and the signal intensity ratio and T2-relaxation time have been shown to correlate with clinical activity scores.14Clinical Radiology. Magnetic resonance imaging of the orbits in thyroid-associated orbitopathy15Ophthalmic Plastic & Reconstructive Surgery. Magnetic Resonance Imaging in the Management of Thyroid Eye Disease: A Systematic Review This matters because the choice between aggressive anti-inflammatory treatment and waiting for the disease to burn out depends heavily on whether the disease is still active.
Corticosteroids as First-Line Treatment
For moderate to severe active TED, intravenous corticosteroids have been the traditional backbone of treatment. IV methylprednisolone is preferred over oral steroids because it is both more effective and better tolerated. In one comparison, IV treatment achieved a response in about 77% of patients versus 51% for those on oral prednisone. Higher cumulative doses tend to work better in the short term, but the advantages fade over time, and doses above 8 grams of cumulative methylprednisolone raise the risk of serious liver toxicity.16PubMed Central. Updates on the understanding and management of thyroid eye disease
The treatment does work. Studies have shown that high-dose IV methylprednisolone improves eyelid swelling, eye pain, light sensitivity, tearing, double vision, and eye bulging, with generally manageable side effects.17PubMed Central. Short and long-term effects of high-dose intravenous methylprednisolone pulse therapy on thyroid-associated ophthalmopathy It also reduces the thickness of swollen eye muscles.18Ophthalmologica Indonesiana. Intravenous Corticosteroid Effects on Superior and Inferior Rectus Muscle in Thyroid Eye Disease But steroids suppress the immune system broadly and come with a well-known list of potential side effects including weight gain, elevated blood sugar, mood changes, and bone thinning. They also do not address the specific molecular pathway driving TED.
Teprotumumab and the Shift Toward Targeted Treatment
The approval of teprotumumab in 2020 marked the first FDA-approved medical therapy for TED and fundamentally changed how the disease is managed. Teprotumumab is a monoclonal antibody that blocks the IGF-1 receptor, directly targeting the signaling pathway that drives orbital inflammation and tissue expansion.19PubMed. Teprotumumab for the Treatment of Thyroid Eye Disease
The pivotal phase 3 trial enrolled 83 patients with active TED and compared eight infusions of teprotumumab to placebo over 21 weeks. The results were striking. At 24 weeks, 83% of patients on teprotumumab had a meaningful reduction in eye bulging, compared to 10% on placebo. Double vision improved in 68% of teprotumumab patients versus 29% on placebo. Quality of life scores, clinical activity, and overall response all showed large advantages for the drug.20PubMed. Teprotumumab for the Treatment of Active Thyroid Eye Disease
Pooled data from both randomized trials showed that about 77% of patients who received teprotumumab achieved at least a 2-mm reduction in proptosis, with a number needed to treat of 1.6, which is unusually strong for any medical intervention. Most patients maintained their response over the long term.21The Lancet Diabetes & Endocrinology. Long-term efficacy and safety of teprotumumab in patients with thyroid eye disease
Teprotumumab is not without drawbacks. It is expensive, typically costing tens of thousands of dollars per infusion cycle, and access varies significantly by insurance plan and country. Side effects include hearing changes (some patients develop hearing loss or tinnitus), muscle spasms, and increased blood sugar. Some patients relapse after completing the infusion course and need retreatment. Still, for many people with active TED, it represents a qualitative leap over what was available before.
Other Biologic Options
For patients who cannot access teprotumumab or who have steroid-resistant disease, two other biologic drugs have shown promise. Tocilizumab, which blocks the immune signaling molecule IL-6, and rituximab, which depletes B cells, have both been used off-label. In a head-to-head comparison of 21 patients with steroid-resistant TED, all seven patients treated with tocilizumab achieved the primary outcome, compared to 9 of 14 on rituximab. Relapses were also less common with tocilizumab, though the study was small.22PubMed. Tocilizumab versus Rituximab in Patients with Moderate to Severe Steroid-resistant Graves’ Orbitopathy Neither drug has a formal TED indication, so their use depends on clinical judgment and local access.
Orbital Radiotherapy
Low-dose radiation aimed at the tissue behind the eyes has been used as a TED treatment for decades, though its role has been debated. A large randomized trial called CIRTED tested the combination of azathioprine (an immunosuppressant) and orbital radiotherapy and found that azathioprine provided benefit but radiotherapy on its own did not significantly improve outcomes.23The Lancet Diabetes & Endocrinology. Combined immunosuppression and radiotherapy in thyroid eye disease (CIRTED) However, when combined with corticosteroids, radiotherapy appears to offer a protective effect against the development of compressive optic neuropathy and improves eye muscle function more than steroids alone.24PubMed. Reduced risk of compressive optic neuropathy using orbital radiotherapy in patients with active thyroid eye disease So radiotherapy is less a standalone treatment and more of a useful add-on in certain patients, particularly those at higher risk of optic nerve compression.
When Surgery Becomes Necessary
Once TED enters the inactive phase and the inflammation has settled, many patients are left with permanent changes: protruding eyes, scarred and stiff eye muscles causing persistent double vision, retracted eyelids, and altered facial appearance. These problems are addressed surgically, and by convention the procedures are done in a specific order: orbital decompression first (removing bone and fat to let the eyes settle back), then strabismus surgery to realign the eye muscles and correct double vision, then eyelid surgery to fix retraction and swelling.25PubMed. Advances in surgical rehabilitation in thyroid eye disease26Thyroid Eye Disease. Sequence and Timing of Surgery for TED The staging exists because each surgery changes the anatomy for the next one: decompression shifts the globe position, which affects muscle alignment, which in turn affects eyelid position.
Not every patient needs all these steps. Some only need eyelid surgery. Others need the full sequence. And some surgeons are now exploring whether multiple stages can be safely combined into a single operation. A study of patients who underwent simultaneous orbital decompression, strabismus surgery, and eyelid correction found outcomes comparable to the traditional multi-step approach, with the obvious advantage of fewer surgeries and a shorter overall rehabilitation timeline.27PubMed. Single-stage Orbital Decompression, Strabismus and Eyelid Surgery in Moderate to Severe Thyroid Associated Orbitopathy
In emergencies, surgery does not wait for the disease to become inactive. Compressive optic neuropathy, where swollen muscles squeeze the optic nerve and threaten permanent vision loss, requires urgent decompression. Even in cases where vision has been completely lost, emergency endoscopic decompression through the nose to relieve pressure on the inner wall of the eye socket has been shown to restore sight in some patients.28PubMed. Reversal of No Light Perception in Dysthyroid Optic Neuropathy by Emergency Endoscopic Endonasal Orbital Decompression
Selenium for Mild Cases
For people with mild TED who do not meet the threshold for steroids or teprotumumab, the evidence base is thinner. One well-known randomized trial tested selenium supplementation (200 micrograms daily) against pentoxifylline and placebo in patients with mild Graves’ orbitopathy. At six months, selenium improved quality of life, slowed disease progression, and reduced eye involvement compared to placebo. Pentoxifylline did not show the same benefits.29PubMed. Selenium and the course of mild Graves’ orbitopathy European guidelines now recommend selenium supplementation as a first-line measure for mild TED. It is cheap, well-tolerated, and one of the few things patients can do on their own while monitoring the disease.
TED in Children
TED is rare in children, but it does occur. When it does, the presentation tends to be milder than in adults. Pediatric patients typically show proptosis and eyelid retraction but are less likely to develop strabismus, vision loss, or optic neuropathy.30PubMed. Pediatric Thyroid Eye Disease: Clinical Characteristics and Orbital Decompression Outcomes The milder course may be because children have more compliant orbital tissues and a less established autoimmune process. That said, the diagnosis is easy to miss in younger patients because pediatricians may not associate eye changes with thyroid disease, and the symptoms can be subtle.
The Psychological Toll
TED changes how people look, and that change affects more than vanity. The bulging eyes, eyelid retraction, and staring gaze can profoundly alter someone’s appearance and how others react to them. A large patient survey found that negative impacts on quality of life, sleep, depression, anxiety, and work productivity were reported across all severity groups, not just those with severe disease.31PubMed Central. Impacts of Thyroid Eye Disease (TED), Beyond the Signs and Symptoms: Results from the ElevaTED Patient Survey People with only mild TED still reported meaningful psychological distress. This is a part of the disease that clinical metrics like the Clinical Activity Score do not capture well. Someone whose proptosis measures a modest 2 mm above normal may still feel deeply self-conscious, withdraw from social situations, and struggle at work. The psychological dimension is real and worth discussing with a care team, not just as a footnote but as a core part of TED management.