What Is Thyroid Eye Disease: A Comprehensive Overview

The thyroid gland is an endocrine gland located in the neck that produces the hormone thyroxine, which controls various functions of the human body. The thyroid hormone¹ regulates the Basal Metabolic Rate (BMR) and heat production, promotes brain and bone growth, and checks the metabolism of different substances.

Thyroid disease is characterized by deranged levels of thyroid hormones and can manifest with a spectrum of symptoms clinically. It can be due to either an underactive thyroid gland or an overactive thyroid gland.

But, what is thyroid eye disease, and how does a problem in some gland in the neck cause such alarming effects in the eye? To know all about the disease and its cure, go through this article till the end.

What Is Thyroid Eye Disease (TED)?

Thyroid eye disease is essentially an autoimmune disorder² that affects the orbital tissue and is seen most commonly in people with thyroid dysfunction. Rarely, this can also be seen in people with normal thyroid levels.

An autoimmune disorder is when the human body’s protective guards – the immune system – launch an abnormal immune reaction against its cells instead of foreign pathogens. This abnormal immune response causes widespread damage to healthy tissue.

Causes of Thyroid Eye Disease

An overactive thyroid gland produces increased levels of thyroid hormones, which is known as hyperthyroidism in clinical terms. One of the common causes of hyperthyroidism is an autoimmune condition called Graves’ disease³.

In Graves’ disease, our body’s immune cells produce autoantibodies against the normal thyroid cells and the receptors on their surface. This results in the overproduction of thyroid hormones which manifests as increased BMR leading to heat intolerance, weight loss, increased heart rate, blood pressure, menstrual disturbances, etc.

It is said that the autoantibodies produced in Graves’ disease do not just attack the thyroid gland but also the eye muscles and connective tissues in the eye socket, leading to thyroid eye disease. Thus, Thyroid Eye Disease (TED) is also called Graves’ eye disease or Graves’ orbitopathy⁴.

Much research is underway to find out what is thyroid eye disease’s exact cause and how it progresses.

The Course of Thyroid Eye Disease

1. Onset of Eye Disease

The thyroid eye disease can present as early as 6 months after diagnosing underlying thyroid disorders such as Graves’ disease. The eye disease progresses in a couple of years and may leave long-term effects in some severe cases.

In Graves’ disease, the abnormal antibodies produced are called thyroid-stimulating autoantibodies. These autoantibodies act on the TSH (Thyroid Stimulating Hormone)⁵ receptors and cause excessive stimulation of the thyroid gland, resulting in hyperplasia of thyroid cells.

In addition, these autoantibodies attack the eye tissues, which contain similar proteins as that of the thyroid gland. The affected structures include the orbital fatty tissue, eye muscles, and connective tissue in orbit. As a result, there is progressive swelling, inflammation, and scarring.

2. Progression of Graves’ Eye Disease

The ongoing inflammation and scarring lead to the progression of eye disease. The disease progression is marked by worsening symptoms such as excessive eye pain, watering, restriction of eye movements, double vision, and even vision loss. All these complaints should be addressed to an eye doctor, and immediate treatment should be initiated.

Now that we know what is thyroid eye disease, its causes, and how it progresses, let us look at the prevalence of the condition.

Prevalence of Thyroid Eye Disease

1. Age

Graves’ eye disease is commonly seen in middle age, and the mean age of onset of eye symptoms from the diagnosis of thyroid disease is 2.5 years.

2. Sex

According to research conducted on Graves’ eye disease, the incidence of the eye disease is more in women (16 per 1,00,000 population) than in men (2.9 per 1,00,000 population). The difference might be compared to the fact that thyroid disorders are more common in females than males.

3. Thyroid Status

Patients with hyperthyroidism are more likely to develop thyroid eye disease. However, it has also been associated with hypothyroidism and even euthyroid states (normal thyroid hormone levels). Global study results reveal that the prevalence of thyroid eye disease in hyperthyroid patients was 86.2%, in hypothyroid patients was 10.36%, and 7.9% in individuals with normal hormone levels.

What Are the Risk Factors That Predispose an Individual to Thyroid Eye Disease?

If present in a person with Graves’ disease or other thyroid disorders, certain traits increase their chances of developing thyroid eye disease. Those factors include:

• Female sex
• Smoking – both active and passive
• Genetic predisposition
• Radioiodine therapy
• Other autoimmune diseases include Type 1 Diabetes mellitus, Rheumatoid arthritis, and Lupus (SLE).
  

Therefore, one with the above-mentioned risk factors must take caution and follow up regularly with their endocrinologist and ophthalmologist. Smoking cessation is imperative as it can worsen thyroid eye disease so that complete loss of vision might ensue.

Read more about what is thyroid eye disease.

What Is Thyroid Eye Disease’s Clinical Picture?

A person with Graves’ eye disease or thyroid eye disease can be singled out in a crowd by the bulging eyes and the blank and staring look on their face. It is most often accompanied by a swelling in the neck, which is due to the overactive thyroid gland.

Early Symptoms of Thyroid Eye Disease

Graves’ eye disease symptoms can start occurring as early as months after the diagnosis of Graves’ disease or years later. Also, the eye symptoms one presents can vary from person to person.

Generally, the early symptoms of thyroid eye disease are redness, pain, and irritation of the eyes, which may be associated with excessive watering or dry eyes. But the most prominent feature is the protruding or bulging eyes, known clinically as proptosis or exophthalmos.

Exophthalmos

Exophthalmos⁶ is a characteristic feature of Graves’ orbitopathy and can be unilateral or bilateral. This is due to inflammation which causes the accumulation of hydrophilic substances called glycosaminoglycans behind the eye, leading to the displacement of the involved eye out of the eye socket.

Other Symptoms of Thyroid Eye Disease 

Upper eyelid retraction is another common feature of thyroid eye disease. This leaves the cornea exposed and thus can result in corneal ulceration.

The optic nerve is responsible for carrying the visual signals from the eyes to the brain. The optic nerve can be compressed by the swollen eye and therefore can cause optic neuropathy. Vision loss can be due to corneal ulceration or damage to the optic nerve.

There may be difficulty moving the eyeballs, photophobia (light intolerance), blurred vision, or double vision. Double vision occurs due to fibrosis of eye muscles and can manifest as a squint.

Investigations and Diagnosis

Thyroid eye disease can be diagnosed with the help of blood tests and scans. A simple blood test specifically known as the thyroid function test is done to study the thyroid hormone levels. It will reveal the underlying problem with the thyroid gland.

Thyroid autoantibodies can also be detected in blood if an autoimmune condition such as Graves’ disease is suspected.

Radiological scans such as Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) of the orbit can be done to visualize the swelling of eye muscles and check for compression of the optic nerve. Other tests to assess the vision may also be ordered.

What Is Thyroid Eye Disease’s Line of Management?

Management of thyroid eye disease is incomplete without treating underlying thyroid dysfunction. The treatment for hyperthyroidism and hypothyroidism is different and should be managed accordingly.

1. Treatment of the Underlying Cause

Anti-thyroid drugs⁷ such as carbimazole, methimazole, or propylthiouracil are given to treat hyperthyroidism. These drugs will reduce the levels of thyroid hormones. To treat hypothyroidism, synthetic preparation of thyroid hormone called levothyroxine is given.

2. Treatment of the Eye Disease

Conservative Methods

Smoking cessation is the first and foremost step in managing thyroid eye disease. Other measures depend on the individual’s symptoms – sunglasses can be worn to prevent photophobia, artificial tears can be used for dry eyes, and prism glasses to correct double vision.

Medical Management

Steroids are prescribed to reduce swelling and inflammation. Other immunosuppressant drugs can also be added if there is no improvement. Recently, the Food and Drug Administration (FDA) has approved a drug called teprotumumab for thyroid eye disease.

Surgery

If double vision is not corrected by using spectacles, there might be a need for eye muscle surgery. In eye muscle surgery, the muscles are detached and reattached properly to normalize the alignment. This is the definitive treatment for double vision.

Eyelid surgery may be needed to correct the retracted upper eyelid. This will ensure that the eyelids adequately cover the cornea and prevent irritation and ulceration.

When the bulging eyes and surrounding swollen tissues are tightly compressed within the eye socket, orbital decompression surgery can relieve the pressure. Orbital decompression surgery involves removing a piece of bone that forms the walls of the orbit, thus allowing more space for the structures inside it.

What Is Thyroid Eye Disease’s Prognosis?

Once proper treatment is ensured, the prognosis of thyroid eye disease is good. Follow-up with an endocrinologist is essential. Regular blood tests are to be done to monitor thyroid function and adjust anti-thyroid drug dosage.

Thyroid eye disease has become a common eye problem over the years. There is much ongoing research on the condition’s cause and treatment for the same. Also, support groups like Thyroid Eye Disease Charitable Trust, Graves’ Disease and Thyroid Foundation, etc., are available for people suffering from the disease.

That concludes the overview of what is a thyroid eye disease. Glance at the following article to learn more about hypothyroidism and hyperthyroidism.

1. Brent, Gregory A. “Mechanisms of thyroid hormone action.” The Journal of clinical investigation 122.9 (2012): 3035-3043. ↩︎
2. Angum, Fariha, et al. “The prevalence of autoimmune disorders in women: a narrative review.” Cureus 12.5 (2020). ↩︎
3. Weetman, Anthony P. “Graves’ disease.” New England Journal of Medicine 343.17 (2000): 1236-1248. ↩︎
4. Dolman, Peter J. “Evaluating graves’ orbitopathy.” Best Practice & Research Clinical Endocrinology & Metabolism 26.3 (2012): 229-248. ↩︎
5. Szkudlinski, Mariusz W., et al. “Thyroid-stimulating hormone and thyroid-stimulating hormone receptor structure-function relationships.” Physiological reviews 82.2 (2002): 473-502. ↩︎
6. Grove Jr, Arthur S. “Evaluation of exophthalmos.” New England Journal of Medicine 292.19 (1975): 1005-1013. ↩︎
7. Brent, Gregory A., and Ronald J. Koenig. “Thyroid and anti-thyroid drugs.” Goodman and Gilman’s the Pharmaceutical Basis of Therapeutics 12 (2002): 1129-62. ↩︎

Last Updated on July 22, 2024 by Sathi Chakraborty, MSc Biology