Enfermedad ocular tiroidea (EOT) is a complex autoimmune condition affecting the tissues around the eyes and is commonly associated with other thyroid conditions, such as Graves’ disease (1). It is caracterizado by inflammation, pain, swelling or protruding eyeballs (proptosis), eyelid retraction or inability to close the eyes completely, eye surface dryness, double vision (diplopia), and in severe cases, compression of the optic nerve (2). When most people think of TED, they imagine both eyes bulging forward and looking unusually wide or irritated (redness and puffiness) (3). Indeed, TED usually affects both eyes, but there is an important caveat that sometimes appears to affect only one eye or is markedly asymmetric, especially early during the course of the disease (4). Awareness of this possibility and the reasons behind it can help patients and clinicians recognize TED symptoms sooner and begin appropriate care (5).
¿Qué es la enfermedad ocular tiroidea?
Thyroid eye disease is an autoimmune inflammatory condition (the body’s immune system starts attacking itself) involving tissues around and behind the eyes, including muscles, fat, and connective tissue. It most often occurs in association with Enfermedad de Graves, but it can also occur in other thyroid diseases or even in the background of a normal thyroid. TED causes inflammation, swelling, eyelid changes, irritation, tearing, double vision, and in more severe cases, optic nerve compression. The common signs and symptoms include:
- Eyelid retraction (incomplete closure of the upper eyelid)
- Redness, puffiness, and swelling around the eyes
- Dryness or a gritty sensation in the eyes
- Proptosis (forward bulging of the eye)
- Visión doble (diplopía)
- Pain or discomfort with eye movement
- Visual field changes or optic nerve involvement
These symptoms typically affect both eyes as TED is a systemic autoimmune process rather than a localized injury. However, TED can disproportionately affect one eye over the other or very rarely, only one eye shows TED-associated changes.
Why TED is Usually Bilateral but Can Also be Asymmetric
Due to the systemic inflammation, most cases of TED affect both orbits, as the antigens that are targeted during the autoimmune attack are uniformly present in both orbital tissues. However, the severity and timing of inflammatory changes can differ between the two sides, leading to asymmetric involvement (6). Investigación has shown that many TED patients show asymmetric orbital involvement and up to 33% to 41% of patients have unilateral TED. Even though asymmetric TED eventually progresses to involving both eyes, a focused study found that roughly 5% to 11% of cases remain as pure unilateral TED. In other words, while most people with TED will gradually involve both eyes, obvious symptoms may first manifest only in one eye or the degree of involvement may differ significantly from one side to the other (7). This can lead to confusion or delayed recognition of the condition.
Reasons for Asymmetric or Unilateral TED
En exact reasons why TED sometimes affects one eye more than the other are not fully understood, but there are many varying hypotheses:
1. Uneven Immune Targeting
Intriguingly, despite its systemic nature, the autoimmune process that drives TED may not act uniformly and the orbit tissues on one side might have a higher concentration of inflammatory cells or react more strongly at a given point of time.
2. Anatomic Differences Between Orbits
Natural anatomical variation and asymmetry between a person’s left and right orbits, including slight differences in bone structure, blood flow, or tissue composition could result in greater inflammation or swelling on one side, especially early in the course of disease.
3. Asymmetric Muscle Enlargement
MRI or CT imaging often shows that enlargement of extraocular muscles (a hallmark of TED) may be more pronounced on one side, resulting in uneven bulging or functional effects such as double vision 8.
Why Unilateral or Asymmetric Symptoms Can Be Misleading
Because TED is typically considered a bilateral condition, clinicians and patients may overlook it when only one eye appears affected, particularly early in the course of the disease. This can delay diagnosis or cause misattribution of symptoms to other conditions, such as orbital cellulitis, orbital tumors, idiopathic orbital inflammatory disease, sinus disease-related swelling, trauma, or infections. Hence, when patients present symptoms, particularly proptosis in one eye alone, these differential diagnoses often come first to mind. So, it is important to suspect TED along with the repertoire of other overlapping diseases, especially when symptoms align with other TED symptoms and a history of thyroid dysfunction.
Confirmation of TED Diagnosis
Due to the above overlapping conditions and similar symptoms, clinicians and specialists often use a comprehensive checklist to both rule out other eye diseases and narrow down on TED during the event of unilateral asymmetric disease.
1. Comprehensive Eye Examination
An eye doctor (optometrist, ophthalmologist or oculofacial plastic surgeon) will undertake several layers of physical examination, which can hint at possible TED:
- Eyelid positioning and movement
- Proptosis using exophthalmometry (measurement of eyelid protrusion)
- Eye movement and alignment
- Signs of inflammation
- Corneal exposure and/or dryness
- Visual acuity and color vision
2. Thyroid Function Tests
Blood tests that evaluate thyroid-stimulating hormone (TSH), T3, T4, and thyroid-related antibodies. Elevated levels of abnormal antibodies or thyroid dysfunction can support the diagnosis. But it is important to note that TED can present without obvious thyroid dysfunction in a minority of patients.
3. Orbital Imaging
When presentation is unilateral or asymmetric, CT or MRI of the orbits is fundamental to confirming TED. These scans can show extraocular muscle enlargement, increased orbital fat volume, infiltration and inflammation behind the eye, and compression of adjacent structures. These characteristic patterns on imaging help distinguish TED from other orbital pathologies, such as tumors or inflammatory pseudotumors.
Why Early Evaluation of Both Eyes Is Important
Even when only one eye seems affected, early and thorough evaluation of both eyes is critical for several reasons:
Prevent Progression and Complications
TED invariably evolves and what begins as a unilateral condition will eventually become bilateral. Early detection allows clinicians to monitor changes over time with timely initiation of therapies (e.g., steroids, biologics), particularly during the active inflammatory phase when they are the most effective. It also helps prevent complications such as optic nerve compression and severe dry eye caused by eyelid retraction. Overlooking early signs, especially in the “less affected” eye, can mean missing the window for optimal treatment.
Symmetric Assessment Prevents Under-Treatment
Symptoms like dry eye, redness, or subtle eyelid lag can appear in both eyes even when only one protrudes more prominently. Evaluating both sides ensures that subtle signs are not overlooked and that treatment plans account for the full scope of the disease.
Accurate Monitoring of Disease Activity
Tracking both eyes over time, even when one appears normal at first, allows clinicians to gauge whether TED activity is stabilizing, improving, or worsening. This is essential in tailoring therapy and deciding whether interventions such as immune modulation, orbital radiotherapy, or surgery are warranted.
Even Subtle or One-Sided Eye Symptoms Deserve Expert Attention
Thyroid eye disease symptoms most often affect both eyes, but asymmetric presentation is common, and true unilateral TED is rare (around 5–11 % of cases remain unilateral). The asymmetry arises from uneven immune targeting, anatomical differences, or early-stage disease dynamics. Also, unilateral or markedly asymmetric signs can mimic other orbital problems, making accurate clinical assessment and imaging essential. Simultaneous confirmatory evaluation should also include thyroid labs, detailed ophthalmic exams, and orbital imaging to differentiate TED from other causes of proptosis.
If you are noticing eye discomfort, swelling, redness, bulging, double vision, or changes in eyelid position, especially if you have a thyroid condition, schedule an appointment with Dr. Raymond Douglas without delay.
Referencias
- Shah, S. S. y Patel, B. C. en StatPearls (2025).
- Johnson, B. T., Jameyfield, E. y Aakalu, V. K. Neuropatía óptica y diplopía por enfermedad ocular tiroidea: actualización sobre fisiopatología y tratamiento. Opinión actual sobre neurología 34, 116-121 (2021). https://doi.org/10.1097/WCO.0000000000000894
- Wiersinga, W. M., Eckstein, A. K. & Zarkovic, M. Thyroid eye disease (Graves’ orbitopathy): clinical presentation, epidemiology, pathogenesis, and management. Lancet Diabetes Endocrinol 13, 600-614 (2025). https://doi.org/10.1016/S2213-8587(25)00066-X
- Rana, K.y otros. Asymmetric proptosis in thyroid eye disease. Int Ophthalmol 44, 206 (2024). https://doi.org/10.1007/s10792-024-03141-6
- Strianese, D.y otros. Unilateral proptosis in thyroid eye disease with subsequent contralateral involvement: retrospective follow-up study. BMC Ophthalmol 13, 21 (2013). https://doi.org/10.1186/1471-2415-13-21
- Antonelli, A. & Benvenga, S. Editorial: The Association of Other Autoimmune Diseases in Patients With Thyroid Autoimmunity. Front Endocrinol (Lausana) 9, 540 (2018). https://doi.org/10.3389/fendo.2018.00540
- Tran, A. Q.y otros. Evolution of asymmetric proptosis during the active phase of thyroid eye disease. Orbit 42, 251-255 (2023). https://doi.org/10.1080/01676830.2022.20888078 Luccas, R., Riguetto, C. M., Alves, M., Zantut-Wittmann, D. E. & Reis, F. Computed tomography and magnetic resonance imaging approaches to Graves’ ophthalmopathy: a narrative review. Front Endocrinol (Lausana)14, 1277961 (2023). https://doi.org/10.3389/fendo.2023.1277961
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