Overview

Thyroid Eye Disease (TED), also known as Graves’ Orbitopathy (GO), is an autoimmune condition that affects the tissues around the eyes. It is most commonly linked to Graves' disease, but it can also occur in patients with Hashimoto’s thyroiditis.¹,² 

TED is tested based on characteristic signs and symptoms, including bulging eyes, double vision, eye movement restriction, eyelid retraction, and swelling around the eyes.³ The disease starts by making the eyes feel pain, after a while the symptom can worsen and the can cause a permanent change in the appearance of your eyes.⁴

Imaging techniques including CT, MRI, and ultrasound, can help assess disease severity, identify complications, and guide treatment decisions.⁵

This article explores how different imaging techniques are used to evaluate TED, providing insight into their benefits, limitations, and role in understanding the disease. Early detection is crucial, as TED can lead to serious complications, including vision loss, if left untreated.⁶

Pathophysiology and clinical features of TED 

Epidemiology 

Thyroid Eye Disease (TED) is a rare condition, affecting mostly persons assigned female at birth, approximately 0.54–0.9 per 100,000 men and 2.67–3.3 per 100,000 women each year.^1,7 Graves' orbitopathy (GO) occurs in about 25%–40% of cases at different stages of the disease. There are several key risk factors that contribute to its onset.

Risk factors for thyroid eye disease

• Gender - Mostly persons assigned female at birth are five times more likely to get Graves’ eye disease⁸
• Age - There is a bimodal peak incidence. Occurs in age groups of 40 to 44 years and 60 to 64 years in persons assigned female at birth and ages of 45 to 49 years and 65 to 69 years in persons assigned male at birth⁸
• Ethnicity -The African-American population has the greatest risk, followed by the White and Asian populations (Shah et al, 2025)
• Smoking – The strongest modifiable risk factor ( ratio 1:7.7)⁹ 
• Thyroid dysfunction – Imbalances in thyroid hormone levels both hyper and hypothyroidism¹
• Radioiodine therapy – A treatment for hyperthyroidism that has a small risk of worsening symptoms¹ 
• Elevated TSH receptor antibodies (TRAbs) – Higher levels are associated with greater disease severity¹ 
• Oxidative stress – Cellular damage that contributes to inflammation¹ 
• High cholesterol (hypercholesterolemia) Can make the outcome of the disease worsen¹
• Genetic predisposition – Family history of autoimmune thyroid disorders
• Environmental triggers – Stress and excessive iodine intake¹⁰,¹¹

Pathogenesis 

TED is an autoimmune disorder where autoantibodies (target the body's own tissues) - TSHR-Ab, activate orbital fibroblasts, leading to inflammation and expansion of orbital tissues.¹⁰ The orbital fibroblasts are special cells in the eye socket that help maintain its structure, support tissue repair, and contribute to inflammation and scarring in conditions like Graves' ophthalmopathy. The activation of orbital fibroblasts produce extracellular matrix, resulting in the immune response from B- and T-cells, mast cells, and macrophages to the orbital tissue.¹² Therefore, causing the swelling of extraocular muscle, excessive fat accumulation, and fluid retention, causing bulging eyes and restricted eye movement.¹³ 

Figure 1. Immune Mechanisms in Thyroid Eye Disease (TED) ¹⁴

The figure illustrates how T cells and B cells drive inflammation by releasing thyroid-stimulating autoantibodies (TSHR-Ab) and IGF-1R antibodies, which activate orbital fibroblasts. Autoantibodies generated against the thyrotropin receptor, orbital cells causing the activation of an inflammatory cascade mediated by cytokines and ultimately ending in the deposition of glycosaminoglycans in the extraocular muscles (EOM) of the orbit. This leads to two fibroblast responses: Type I fibroblasts increase fat production, while Type II fibroblasts contribute to scar formation. Source: (Scarabosio et al., 2024).¹⁴

Key clinical features 

TED presents with a variety of symptoms, ranging from mild irritation to significant orbital complications 1. Early signs include puffiness around the eyes, eyelid retraction, excessive tearing, and eye redness.¹³ In severe cases, optic nerve compression can result in reduced vision.¹⁰ Hallmark features of TED include eyelid retraction, bulging eyes (proptosis), and double vision (diplopia).¹² Upper eyelid retraction is the most common feature observed in over 90% of TED patients.¹⁵ Imaging techniques such as CT, MRI, and ultrasound are essential for assessing disease severity, differentiating TED from other orbital disorders, and guiding treatment decisions.¹⁰

Figure 2. Schematic representation of the clinical manifestations of thyroid eye disease. The most common clinical symptoms involved in thyroid eye disease are depicted in this illustration. Source: (Kulbay et al, 2024) .¹² 

Figure 3 Key Clinical Feature in TED. Upper Eyelid Retreaction (Courtesy of P Perros).¹⁵

Disease progression

Thyroid eye disease (TED) progresses through two distinct stages, which are evaluated using clinical scoring systems like the Clinical Activity Score (CAS) and NOSPECS classification (Johnson et al,2021).The European Group on Graves’ Orbitopathy (EUGOGO) has three categories of TED severity: mild, moderate-to-severe and sight threatening.¹⁶,¹⁷ The early, active phase involves inflammation and deposition of extracellular matrix components in the orbital tissues, resulting in swelling and tissue remodeling. Later, the inactive phase involves fibrosis and scarring, which reduces the elasticity of the extraocular muscles (EOM), often resulting in restrictive myopathy.¹⁸ A thorough understanding of these disease mechanisms is essential for interpreting imaging findings across different modalities, particularly MRI, and assessing disease severity and activity in TED.¹⁸

Role of CT (Computed Tomography) 

A CT( Computed Tomography) scan provides superior, detailed images of bones and soft tissue and is essential for guiding the management of TED¹² It is primarily used to assess extraocular muscle hypertrophy, orbital fat expansion, and potential optic nerve compression.¹⁹Additionally, CT is essential for preoperative planning in orbital decompression surgery.¹²

Key Findings on CT:

• Extraocular Muscle Enlargement: TED typically affects the inferior rectus first, followed by the superior rectus, medial rectus, and, less commonly, the lateral rectus¹⁹
• Coca-Cola Sign: The characteristic bowing of the medial orbital wall seen in TED¹² 
• Orbital Fat Prolapse: Increased orbital fat volume contributes to proptosis¹ 
• Optic Nerve Compression: Enlargement of the extraocular muscles and fat accumulation can lead to crowding at the orbital apex, increasing the risk of compressive optic neuropathy¹⁰
• Bony Remodeling: Chronic cases may exhibit remodeling of the orbital walls²⁰

Figure 4 Axial CT in Thyroid Eye Disease : CT shows enlarged medial rectus muscles and remodeling of the medial orbital walls, forming the "Coca-Cola sign" due to their characteristic bowing shape. Source : Ophthalmic Plastic & Reconstructive Surgery34(4S):S41-S51, July/August 2018 .¹⁸ 

Advantages of CT in TED

• High spatial resolution – Provides detailed imaging of orbital structures¹² 
• Detects hallmark TED findings – Identifies extraocular muscle hypertrophy (tendon-sparing enlargement), orbital fat prolapse, and optic nerve compression¹⁹
• Preoperative planning – Essential for orbital decompression surgery¹ 
• Rapid and readily available – Offers fast imaging with widespread accessibility²⁰
• Natural contrast between tissues – Differentiates fat, muscle, bone, and optic nerve structures without needing intravenous contrast in many cases²⁰

Limitations of CT in TED

• Radiation exposure – Ionising radiation limits repeated imaging for long-term monitoring¹ 
• Limited in differentiating active disease – Cannot reliably distinguish between inflammation and fibrosis²⁰
• Less effective for soft tissue assessment – Lacks the soft-tissue contrast detail provided by MRI¹² 
• Potential metal artefacts – Dental implants or metal prosthetics can distort images²⁰

Role of MRI (Magnetic Resonance Imaging) 

Magnetic Resonance Imaging (MRI) is a non-invasive imaging technique that provides high-resolution soft tissue contrast, making it essential for assessing thyroid eye disease (TED).²¹ MRI works by exploiting the behaviour of hydrogen nuclei, which act as small magnets in a strong magnetic field. A radio-frequency (RF) pulse excites these protons, and as they return to their original state, they emit signals detected as T1 and T2 relaxation times. T1-weighted (T1w) images highlight anatomical structures, while T2-weighted (T2w) images differentiate inflamed from fibrotic tissues.^{20, 23}

Figure 5 MRI Measurements in GO

(A–C) Show proptosis, extraocular muscle thickness, and orbital fat measurements, with medial and lateral rectus muscles assessed in axial images. (D) Dixon-T2WI sequence evaluates signal intensity using SIR. Source: Song et al,2022.²²

Key findings

• Detecting optic nerve compression, especially in dysthyroid optic neuropathy (DON)¹² 
• Differentiating active inflammation from fibrosis²²
• Assessing orbital fat volume, extraocular muscle (EOM) involvement, and lacrimal gland changes¹⁵

Advantages

• Safe, no ionizing radiation¹⁵
• Superior soft tissue contrast for detecting inflammation, edema, and fibrosis¹² 
• Advanced imaging sequences like STIR and Diffusion-Weighted Imaging (DWI) enhance disease activity detection²²

MRI Findings in TED

• T2-weighted (T2w) images: Active TED appears hyperintense due to muscle inflammation and edema¹² 
• T1-weighted post-contrast (T1w+C) images: Highlighted edematous tissues and disease activity²¹
• Commonly affected muscles: The superior and inferior rectus, sparing tendinous insertions²²

Limitations

• Longer scan times¹⁵
• Higher cost and limited availability compared to CT²²

MRI is a crucial tool in TED, aiding in disease assessment, treatment planning, and detecting optic nerve involvement.

Role of ultrasound 

Ultrasound is a useful initial imaging tool in TED, particularly in outpatient settings. It helps in monitoring disease progression and evaluating treatment response.¹⁰

Key findings

Key sonographic features include extraocular muscle thickening, muscle & fat proliferation, and increased muscle reflectivity, which indicates active inflammation. Doppler ultrasound can assess vascularity, aiding in the differentiation of active and inactive disease.²⁴

Advantages

Ultrasound is non-invasive, cost-effective, and radiation-free, making it ideal for serial monitoring. It allows precise measurement of extraocular muscle thickness and detection of orbital fat changes. Moreover, it is widely available and can be performed in ophthalmology clinics.¹⁹

Limitations

Ultrasound is operator-dependent, with limited ability to visualize deep orbital structures, such as the orbital apex. While effective in detecting muscle enlargement, it is less sensitive than CT and MRI for assessing disease severity and complications, including optic neuropathy.²⁵

Despite limitations, ultrasound is a valuable tool for monitoring TED progression and providing an accessible, safe option when more advanced imaging is unavailable.²⁵

Summary 

• Early diagnosis and preventive measures are essential to slow TED progression
• Contrast-enhanced CT or MRI is useful in severe or atypical cases to assess disease activity and rule out other conditions
• A multimodal imaging approach improves diagnostic accuracy and treatment planning, with noncontrast CT preferred for surgical candidates
• Advances in neuroimaging have enhanced the detection of orbital and brain changes in TED, aiding in prognosis
• Innovations like image-guided surgery using intraoperative CT and MRI improve precision, reducing complications such as optic nerve damage and strabismus