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PubMed This is a summary of 20 peer-reviewed journal articles Updated
Ophthalmology · Thyroid Eye Disease (Graves' Orbitopathy)

Tracking the Journey: Activity, Severity, and the Disease Timeline

At a Glance

Thyroid eye disease can be active without being severe, or severe after inflammation has stopped. Doctors combine symptoms, an inflammation score, eye function, disease changes, and sometimes MRI to decide how the condition is progressing and when treatment may help.

Navigating Thyroid Eye Disease (TED) can feel like trying to hit a moving target. Because the disease changes over time, doctors use two very different “yardsticks” to measure it: Activity (is there active inflammation?) and Severity (how much functional or cosmetic impact has it caused?).

Understanding where you are in the disease course is the first step in deciding whether you need anti-inflammatory medical treatments now or rehabilitative surgery later.

Rundle’s Curve: A Historical Model

In the 1940s, a doctor named Francis Rundle described a general historical model of the typical TED “life cycle,” now known as Rundle’s Curve [1]. While it is a helpful concept, it is not a strict timetable, and every person’s experience varies. The disease generally follows a biphasic (two-phase) path:

  1. The Active Phase: This is the inflammatory period where the immune system is actively attacking the eye tissues. You may notice increasing redness, swelling, and pain. While historically estimated to last between 18 and 24 months, activity can resolve sooner, persist longer, or relapse [2][3].
  2. The Plateau/Inactive Phase: Eventually, the inflammation settles down into a stable phase. While the active inflammation is gone, it often leaves behind structural changes like scarring (fibrosis), bulging eyes (proptosis), or double vision (diplopia) [2][4].

It is important to know that some patients have “quiet” TED where they experience progressive changes without obvious redness or swelling, and others may experience a recurrence of inflammation even after the disease has stabilized [5][6].

Activity vs. Severity: Two Different Measures

One of the most confusing parts of a TED diagnosis is that a “mild” case can be highly active, and a “severe” case can be completely inactive.

  • Activity refers to current inflammation. If your eyes are red, painful, or getting worse every week, your disease is “active” [7].
  • Severity refers to the functional and cosmetic impact on your life. If you have permanent double vision or significant bulging that makes it hard to close your eyelids, your disease is “severe,” even if the inflammation has stopped [8][9].

The Clinical Activity Score (CAS)

Doctors use the Clinical Activity Score (CAS) to check for active inflammation. They look for 7 key signs, such as eye pain, redness of the eyelids or whites of the eyes, and swelling of the caruncle (the small pink bump in the inner corner of the eye) [10].

A score of 3 or higher conventionally indicates active disease [10]. However, the CAS has major limitations:

  • The “Quiet” Progressor: You can have a low CAS (1 or 2) and still have disease that is rapidly worsening or even threatening your vision. A low score does not necessarily exclude progression [11][12].
  • Inconsistency: Different doctors may score the same patient differently [13].

EUGOGO Severity Tiers

While the CAS measures the inflammation, the EUGOGO (European Group on Graves’ Orbitopathy) classification measures the severity in three tiers [14][8]:

  1. Mild: The disease has a minor impact on daily life. It may involve slight eyelid swelling or minor bulging.
  2. Moderate-to-Severe: This includes significant bulging, constant double vision, or eyelid retraction that interferes with daily activities.
  3. Sight-Threatening: This is the most serious tier, where the swelling is so severe it compresses the optic nerve (Dysthyroid Optic Neuropathy) or causes the surface of the eye to break down (corneal ulceration) [9][15].

Using MRI to Support the Clinical Exam

When your clinical symptoms are worsening but ambiguous, your doctor may use an MRI for supportive evidence. While the CAS only looks at the surface, an MRI can view the tissues behind the eye [16].

  • Detecting Hidden Edema: Active inflammation often shows up as a “bright” signal on specific MRI sequences (like T2 or STIR). This supports the presence of edema or activity [17][18].
  • Interpreting Results: Conversely, if the muscles look dark, this is helpful information, but it does not definitively prove that anti-inflammatory treatment will not help. An MRI should never delay the treatment of suspected optic neuropathy. Treatment decisions are always made by combining vision, motility, appearance, disease trajectory, examination, and imaging [19][20].

Common questions in this guide

What is the difference between active and inactive thyroid eye disease?
Active thyroid eye disease means inflammation is currently causing or worsening signs such as redness, swelling, pain, or changes in eye movement. Inactive disease means the inflammation has settled, although lasting changes such as bulging eyes, scarring, or double vision can remain. Inflammation can sometimes return, so ongoing changes should be discussed with an eye specialist.
Can thyroid eye disease worsen even if my CAS is low?
Yes. The Clinical Activity Score focuses on selected signs of inflammation, so a low score does not always exclude progression or a threat to vision. Doctors also consider changes in vision, eye movement, appearance, examination findings, and the overall disease course.
What does a CAS of 3 or higher mean?
A Clinical Activity Score of 3 or higher conventionally indicates active thyroid eye disease because several signs of inflammation are present. The score is not a complete measure of disease severity and may vary between examiners. Your clinician should interpret it alongside your vision and other examination findings.
How is thyroid eye disease severity classified?
The EUGOGO system groups thyroid eye disease as mild, moderate-to-severe, or sight-threatening. Classification considers how much the disease affects daily activities, eye appearance, eye movement, vision, and the eye surface. Sight-threatening disease can involve pressure on the optic nerve or breakdown of the cornea.
Can an MRI show inflammation that an eye exam misses?
MRI can show tissue changes behind the eye, and active inflammation may appear as a bright signal on certain sequences such as T2 or STIR. It provides supporting information rather than a definitive answer about treatment response. Clinicians combine MRI with vision, eye movement, appearance, examination findings, and the disease trajectory, and MRI should not delay treatment when optic nerve compression is suspected.
When is surgery considered for thyroid eye disease?
After inflammation has settled and the condition is stable, lasting changes such as bulging, double vision, or eyelid problems may be addressed with rehabilitative surgery or non-surgical management. Timing and options depend on your examination, symptoms, and disease stability. An eye specialist can explain which approach is appropriate.

Get notified when new evidence is published on Euthyroid Graves orbitopathy.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.

References

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This page is for informational purposes only and does not constitute medical advice. An ophthalmologist or other treating clinician should interpret your CAS, imaging, examination findings, and vision changes.

Guide contents Euthyroid Graves orbitopathy
Research & Literature
01 When Thyroid Tests Are Normal 03 Cooling the Fire