Thyroid Eye Disease: Causes, Diagnosis, and Treatment

Thyroid eye disease affects roughly 1 in 1,000 people in the general population, but among those with Graves' disease — the most common cause of hyperthyroidism — the orbital complications appear in an estimated 25–50% of cases (National Eye Institute). The consequences range from cosmetic changes that alter a person's appearance to vision-threatening corneal exposure and optic nerve compression. It is, in short, a condition that deserves more attention than it typically gets outside of endocrinology and ophthalmology clinics.

What Is Thyroid Eye Disease?

Thyroid eye disease (TED) — also called Graves' orbitopathy or Graves' ophthalmopathy — is an autoimmune condition in which the body's immune system attacks the soft tissues and muscles surrounding the eyes. The orbit becomes inflamed, the extraocular muscles swell, and fatty tissue behind the eye expands. That expansion pushes the eyeball forward, producing the characteristic proptosis (bulging eyes) associated with the disease.

TED most commonly accompanies Graves' disease, though it can also occur in people with Hashimoto's thyroiditis or even in those with no detectable thyroid dysfunction at all. The thyroid connection is real but imperfect — thyroid function and eye disease activity don't always move in lockstep, which catches patients and physicians alike off guard.

What Causes It?

The underlying mechanism centers on a shared antigen: the thyroid-stimulating hormone receptor (TSHR). In Graves' disease, antibodies called thyroid-stimulating immunoglobulins (TSIs) bind to TSHRs on the thyroid gland — but those same receptors are expressed in orbital fibroblasts. When antibodies activate orbital fibroblasts, the cells proliferate and produce glycosaminoglycans, particularly hyaluronan, which attracts water and causes tissue swelling (American Thyroid Association).

Insulin-like growth factor-1 receptor (IGF-1R) also plays a role, forming a complex with TSHR that amplifies the inflammatory response. This receptor pairing became clinically significant when it emerged as the target for teprotumumab, the first FDA-approved treatment specifically designed for TED.

Smoking is the single most consistently documented modifiable risk factor. Smokers with Graves' disease face an approximately 8-fold higher risk of developing significant orbitopathy compared to non-smokers, and the disease tends to be more severe (Tobacco Control, BMJ Publishing Group). Radioactive iodine therapy for hyperthyroidism can also trigger or worsen TED in susceptible individuals, particularly in smokers.

Recognizing the Symptoms

TED tends to announce itself gradually. Early symptoms include:

TED follows a biphasic course described by the Rundle curve: an active inflammatory phase lasting 6 months to 2 years, followed by a plateau and then a stable, inactive phase. Treatment timing relative to this curve significantly affects outcomes.

Diagnosis

No single test confirms TED. Diagnosis is clinical, supported by imaging and laboratory findings.

Clinical assessment uses the Clinical Activity Score (CAS), a 7-point scale rating pain, redness, and swelling. A CAS of 3 or higher indicates active inflammation. The European Group on Graves' Orbitopathy (EUGOGO) guidelines stratify disease severity into mild, moderate-to-severe, and sight-threatening categories (EUGOGO guidelines via Thyroid journal, Mary Ann Liebert).

Laboratory tests typically include TSH, free T4, free T3, and TSI (or TRAb — TSH receptor antibody) levels. Elevated TRAb supports the diagnosis, though levels don't predict severity.

Orbital imaging — CT or MRI — visualizes muscle enlargement, optic nerve compression, and helps distinguish TED from orbital pseudotumor, lymphoma, or other conditions that can mimic it. CT scans show the classic "muscle belly sparing of tendon insertion" pattern characteristic of TED.

Treatment

Active Phase: Reducing Inflammation

Intravenous glucocorticoids — typically high-dose methylprednisolone administered in weekly pulses — remain the first-line treatment for moderate-to-severe active TED. EUGOGO recommends a cumulative dose not exceeding 8 grams per cycle (EUGOGO, European Journal of Endocrinology). Oral steroids are less effective and carry a higher side-effect burden.

Teprotumumab (Tepezza) is a monoclonal antibody targeting IGF-1R, approved by the FDA in January 2020 — making it the first medication specifically approved for TED. In phase 3 clinical trials, 83% of patients treated with teprotumumab showed a clinically meaningful reduction in proptosis (≥2 mm) compared to 10% in the placebo group (NEJM, 2020). Infusion-related hearing changes have been identified as a notable adverse effect, prompting audiological monitoring during treatment.

Orbital radiation is used in select cases, typically combined with glucocorticoids, targeting active inflammation with 20 Gy in 10 fractions over 2 weeks.

Inactive Phase: Surgical Rehabilitation

Once disease activity has stabilized for at least 6 months, surgical intervention can address residual structural changes. The sequence matters: orbital decompression surgery is performed first (when needed to relieve proptosis or optic neuropathy), followed by strabismus surgery to correct diplopia, and finally eyelid surgery — always in that order, because each prior step changes the anatomy.

Orbital decompression removes bone from one or more walls of the orbit, allowing displaced fat and muscle to redistribute. Techniques and the number of walls decompressed depend on the degree of proptosis.

Selenium supplementation (200 mcg daily for 6 months) has shown benefit in patients with mild TED in a randomized trial published in the New England Journal of Medicine, reducing disease activity and improving quality of life in selenium-deficient populations (NEJM, 2011).

References

The law belongs to the people. Georgia v. Public.Resource.Org, 590 U.S. (2020)