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PubMed This is a summary of 10 peer-reviewed journal articles Updated
Ophthalmology · Thyroid Eye Disease

What Is the Clinical Activity Score for Thyroid Eye Disease?

At a Glance

The Clinical Activity Score (CAS) measures current eye inflammation in thyroid eye disease. A score of 3 or more on the initial 7-point scale or 4 or more on the follow-up 10-point scale commonly indicates active disease, but a low score does not rule out sight-threatening complications.

In this answer

3 sections

01

The 7 Criteria of the Standard CAS

02

Follow-up Visits and the 10-Point Score

03

Why This Matters for Your Care

Your doctor uses the Clinical Activity Score (CAS) to measure how actively inflamed your eyes are right now [1]. It is one part of a comprehensive ophthalmic assessment that helps your care team determine if your thyroid eye disease is in the “active” inflammatory phase or the “inactive” stable phase [2].

Important Safety Warning: The CAS measures inflammation, not whether your disease is sight-threatening [3]. You can have a low score but still experience dangerous complications like optic nerve compression or severe corneal exposure. Seek urgent medical care if you experience new or worsening reduced vision, washed-out color vision, changes in your visual field, severe eye pain, or an inability to fully close your eyelids. Do not wait for your next routine CAS measurement.

The 7 Criteria of the Standard CAS

During your initial exam, the doctor will check for seven specific signs of pain, redness, and swelling [4]. Each sign that is present counts as one point, for a total possible score of 7 [5]. Please note that these must be assessed by a clinician—do not try to calculate your own score at home.

  • Spontaneous pain behind the eye: An aching, throbbing, or pressure feeling behind your eyeball, even when resting [4].
  • Pain when moving the eyes: Discomfort or pain when you attempt to look in different directions, especially upward or downward [5].
  • Redness of the eyelids: Noticeable redness (erythema) on the skin of your eyelids [4].
  • Redness of the whites of the eyes: Bloodshot eyes caused by enlarged blood vessels in the conjunctiva (conjunctival injection) [5].
  • Swelling of the eyelids: Puffiness or fluid buildup (edema) in your upper or lower eyelids [4].
  • Swelling of the conjunctiva: Fluid accumulation in the clear membrane covering the white part of your eye (chemosis), which can look like a blister or jelly-like swelling [5].
  • Swollen caruncle or plica: Inflammation of the small, pink nodule and tissue in the inner corner of your eye [4].

A score of 3 or higher on this 7-point scale is commonly used by doctors to classify thyroid eye disease as currently “active” [6][4].

Follow-up Visits and the 10-Point Score

When you return for follow-up appointments, your doctor may use an expanded 10-point version of the CAS to check for progression [7]. This version includes the original seven signs of inflammation but adds three points for specific, clinically measured worsening of your condition since your last visit [8][9]:

  • An increase in eye bulging (proptosis) of at least 2 millimeters.
  • A decrease in eye movement of at least 8 degrees in any direction.
  • A decrease in visual acuity equivalent to one line on the Snellen eye chart.

For this 10-point scale, a score of 4 or higher generally indicates active disease [9].

Why This Matters for Your Care

Knowing your CAS score helps guide your treatment plan, but it is not the only factor. Your care team will also consider the overall severity of your disease, visual risks, how long you have had symptoms, and your personal preferences [2].

It is important to know that “inactive” disease means the inflammation has quieted down; it does not mean the disease has completely disappeared. You may still have lasting effects like bulging eyes or double vision. Generally, active disease with a high score is managed with anti-inflammatory medications or other urgent therapies, while rehabilitative surgeries (like orbital decompression or eyelid surgery) are usually reserved for when the disease is clinically inactive and stable [2].

Always share any changes in your symptoms with your doctor. The CAS is just one tool, and your daily experience and visual function matter just as much [10][3].

Common questions in this guide

What does a Clinical Activity Score measure in thyroid eye disease?
The Clinical Activity Score (CAS) measures signs of current inflammation in and around the eyes, such as pain, redness, and swelling. It helps clinicians judge whether thyroid eye disease is in an active inflammatory phase or an inactive phase, but it does not by itself show whether the condition is threatening vision.
How is the 7-point CAS calculated?
At an initial examination, a clinician checks seven signs of inflammation. Each sign that is present contributes one point, for a maximum of seven; a score of 3 or more is commonly used to classify the disease as active. Do not try to calculate the score yourself at home.
What is the 10-point CAS used at follow-up visits?
At follow-up, a clinician may use a 10-point CAS that keeps the original seven inflammation signs and adds points for measurable worsening since the previous visit. The added changes include more eye bulging, reduced eye movement, or a drop in visual acuity. A score of 4 or more generally indicates active disease on this scale.
Can thyroid eye disease be dangerous even with a low CAS?
Yes. The CAS reflects inflammation, not all risks to vision, so a low score does not rule out optic nerve compression or severe corneal exposure. Seek urgent medical care for new or worsening reduced vision, washed-out color vision, visual-field changes, severe eye pain, or inability to close the eyelids fully.
Does an inactive CAS mean thyroid eye disease is gone?
No. Inactive disease means the inflammation has quieted, but lasting effects such as eye bulging or double vision may remain. Your doctor can discuss whether monitoring or later rehabilitative surgery is appropriate once the condition is stable.
How does my CAS score affect treatment?
Your CAS helps your care team decide whether anti-inflammatory treatment or other urgent therapy may be appropriate, but it is only one part of the decision. They also consider disease severity, visual risk, symptom duration, examination findings, and your preferences; rehabilitative procedures are usually considered after the disease is inactive and stable.

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Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What was my total Clinical Activity Score today, and which specific signs were present?
  2. 2.Did you use the 7-point or the 10-point scale for my exam?
  3. 3.Based on my score and other exams, is my thyroid eye disease considered active or inactive right now?
  4. 4.Are there any signs of sight-threatening complications that the CAS doesn't cover?
  5. 5.How does my current CAS change the treatment options available to me?

References

References (10)
  1. 1

    The 2021 European Group on Graves' orbitopathy (EUGOGO) clinical practice guidelines for the medical management of Graves' orbitopathy.

    Bartalena L, Kahaly GJ, Baldeschi L, et al.

    European journal of endocrinology 2021; (185(4)):G43-G67.

    PMID: 34297684
  2. 2

    Updates on Treatment in Thyroid Eye Disease for the Neurologist.

    Alryalat SA, Alasheh A, Salim QA, Yaaqba N

    Neurologic clinics 2026; (44(2)):321-335 doi:10.1016/j.ncl.2025.12.002.

    PMID: 41922040
  3. 3

    Assessment of disease activity in Graves' orbitopathy.

    Potvin ARGG, Lacraru IC, Bisschop PH, et al.

    Frontiers in ophthalmology 2025; (5()):1697892 doi:10.3389/fopht.2025.1697892.

    PMID: 41384130
  4. 4

    Grading Severity and Activity in Thyroid Eye Disease.

    Dolman PJ

    Ophthalmic plastic and reconstructive surgery 2018; (34(4S Suppl 1)):S34-S40 doi:10.1097/IOP.0000000000001150.

    PMID: 29952931
  5. 5

    Machine learning-assisted system using digital facial images to predict the clinical activity score in thyroid-associated orbitopathy.

    Moon JH, Shin K, Lee GM, et al.

    Scientific reports 2022; (12(1)):22085 doi:10.1038/s41598-022-25887-8.

    PMID: 36543834
  6. 6

    Teprotumumab for Thyroid-Associated Ophthalmopathy.

    Smith TJ, Kahaly GJ, Ezra DG, et al.

    The New England journal of medicine 2017; (376(18)):1748-1761 doi:10.1056/NEJMoa1614949.

    PMID: 28467880
  7. 7

    Association of Patient Age and the Thyroid Eye Disease-Clinical Activity Score.

    North VS, Zhou HW, Tran AQ, et al.

    Ophthalmic plastic and reconstructive surgery 2023; (39(6S)):S46-S50 doi:10.1097/IOP.0000000000002501.

    PMID: 38054985
  8. 8

    Development of an excel-based decision support tool for graves orbitopathy.

    Kilic D, Aksoy M

    Orbit (Amsterdam, Netherlands) 2026; 1-4 doi:10.1080/01676830.2026.2666295.

    PMID: 42112668
  9. 9

    Rituximab for thyroid-associated ophthalmopathy.

    Kang S, Hamed Azzam S, Minakaran N, Ezra DG

    The Cochrane database of systematic reviews 2022; (6()):CD009226 doi:10.1002/14651858.CD009226.pub3.

    PMID: 35709102
  10. 10

    Inter-observer Variability of Clinical Activity Score: Assessments in Patients With Thyroid Eye Disease.

    Perros P, Žarković M, Pearce SH, et al.

    American journal of ophthalmology 2023; (252()):94-100 doi:10.1016/j.ajo.2023.03.027.

    PMID: 37028695

This page explains how clinicians use the CAS in thyroid eye disease for informational purposes only and does not constitute medical advice or replace an eye examination. Seek urgent medical care for new or worsening vision changes.