Thyroid Eye Disease: Signs, Symptoms & Diagnosis

Part of our complete guide to Thyroid Eye Disease (TED) — this page covers TED diagnosis and evaluation in depth.

Thyroid eye disease is recognized by a characteristic set of eye findings and graded by how active and how severe it is. This page covers the clinical signs, the orbital imaging, and the scoring systems used to guide treatment.

Eye Signs of Thyroid Eye Disease

The hallmark findings of TED include proptosis, lid retraction, restricted eye movement, and periorbital swelling. The combination of these features gives the characteristic “staring” or “startled” appearance.

Clinical Findings

• Proptosis (exophthalmos): Forward displacement of the globe due to expanded orbital volume. Hertel exophthalmometry readings > 21 mm, or ≥ 2 mm of asymmetry between the eyes, are considered significant (normal values vary by ethnicity). Thyroid eye disease is the most common cause of proptosis in adults, and is also the most common cause of bilateral proptosis
• Eyelid retraction: Upper lid scleral show (limbus to upper lid margin >2 mm) and lower lid scleral show below the limbus. Both sympathetic over-stimulation and levator fibrosis contribute
• Restrictive strabismus: Tight, fibrotic extraocular muscles restrict movement and cause diplopia, most commonly on upgaze (inferior rectus) and lateral gaze (medial rectus)
• Periorbital edema and chemosis: Inflammatory swelling of eyelids, conjunctiva, and caruncle
• Corneal exposure keratopathy: Incomplete eyelid closure and reduced blink rate from proptosis and lid retraction expose the cornea — causing dryness, pain, and risk of corneal ulceration
• Compressive optic neuropathy (CON): The most vision-threatening complication — enlarged muscles at the orbital apex compress the optic nerve. Presents with decreased visual acuity, color desaturation, and relative afferent pupillary defect. Requires urgent treatment

Radiological Findings

CT of the orbits characteristically demonstrates enlarged extraocular muscles (particularly inferior and medial rectus) with sparing of the tendinous insertions — a key feature distinguishing TED from orbital myositis, where the tendon is involved. Crowding of the enlarged muscles at the orbital apex (apical crowding) predicts risk of optic neuropathy.

Disease Activity & Severity

TED has two distinct phases: an active (inflammatory) phase of variable duration (typically 6–24 months) followed by an inactive (fibrotic) phase. Timing of treatment is critical — most medical therapies work only during the active phase.

Clinical Activity Score (CAS)

The CAS assigns one point for each of the following signs of active inflammation:

• Spontaneous orbital pain
• Pain on eye movement
• Eyelid erythema
• Conjunctival injection
• Chemosis
• Swelling of the caruncle or plica
• Eyelid edema

A CAS ≥ 3/7 indicates active disease. Active disease may respond to medical therapy such as corticosteroids and the IGF-1R inhibitor teprotumumab (Tepezza); teprotumumab requires monitoring for hearing impairment and hyperglycemia; it can harm a developing fetus, so it must not be used in pregnancy and effective contraception is required during treatment and for 6 months after the final dose; inactive disease does not — surgical rehabilitation is the appropriate approach for stable inactive TED.

Severity Classification

Conservative Management

• Preservative-free lubricating eye drops (frequently) and gel or ointment at night
• Selenium supplementation 200 μg/day for 6 months — shown to slow progression in mild active TED (evidence from selenium-deficient European populations)
• Taping eyelids closed at night for lagophthalmos
• Elevated head of bed to reduce morning periorbital edema
• Prism glasses for diplopia
• Smoking cessation — the single most impactful intervention a patient can make

Orbital & Muscle Anatomy

In TED, the extraocular muscles become infiltrated with inflammatory cells, expand due to glycosaminoglycan deposition, and eventually fibrosis. The inferior and medial rectus muscles are most consistently affected, producing the characteristic upward and outward gaze restrictions and diplopia.