In order to understand thyroid eye disease, it is important to know the function of a normal thyroid. The thyroid is a gland at the bottom of the neck, and it is responsible for producing hormones that control the body’s metabolism. Heart rate, body temperature, and blood pressure are some of the most important aspects of one’s metabolism. When thyroid hormones are elevated, it causes the body to go into a hypermetabolic state that increases heart rate, blood pressure, sweating (and heat intolerance), weight loss, and hair loss. Hyperthyroidism (too much thyroid hormones in the blood) is commonly caused by Graves’ disease, which is an autoimmune condition that affects the production of thyroid hormones. Of the people diagnosed with Graves’ disease, only a fraction have ocular complications. The diagnosis of thyroid eye disease is made when the eyes become involved, to any degree, in response to the thyroid condition.
What causes thyroid eye disease?
When we think of our immune system, we picture our body fighting off a cold or infection. In people with hyperthyroidism caused by Graves’ disease, the body produces an abnormal antibody that fools the body into thinking it is a normal molecule of thyroid-stimulating hormone, or TSH. As these antibodies mimic TSH, the body produces more thyroid hormones (T3 and T4) in response to the signal. This is a type of autoimmune condition, which means the immune system attacks normal, healthy tissues in the body. It is speculated that the tissues around the eye are similar to those of the thyroid and the faulty antibodies “accidentally” attack the eye tissues, in addition to the thyroid.1 This causes progressive inflammation that is detrimental to the tissues around the eyes.
What are the signs and symptoms of thyroid eye disease?
It is common for ocular signs and symptoms to be the first indication of Graves’ disease, which prompts an initial diagnosis and subsequent treatment plan. Symptoms can fluctuate and tend to worsen during periods of active episodes of the disease. When hyperthyroidism affects the eyes, it usually targets the eye muscles, fat and connective tissues around the eye and within the socket. The muscles, fat, and connective tissues enlarge, which makes the eye socket very crowded and eventually painful.
This crowding can lead to proptosis or bulging of the eyes, which gives the classic “staring” appearance, and lid retraction. The eyelids might not be able to fully close during a blink or while sleeping if the eyes are bulging forward. When the eyes are not protected by the eyelids, the cornea (clear front part of eye) tends to dry out. Dry eye syndrome can make the eyes feel gritty and irritated, while they may also water and appear red.
If the eye muscles are restricted or unable to move as fully and/or quickly as they should, strabismus (misalignment of the eyes) and double vision may occur. Similarly to restricted eye muscles, the optic nerve can be compressed in severe cases. If the optic nerve is compressed for too long, the nerve fibers that are responsible for vision can die and cause permanent visual field defects (areas of missing vision).
Once the symptoms and swelling subsides, there may be residual scarring of the muscles and tissues, which can change the “normal” appearance of the eyes.
Who is at risk for thyroid eye disease?
– Women (typically middle-aged) – Cigarette smokers – Personal history of thyroid disease – Family history of thyroid disease
What is the treatment for thyroid eye disease?
Treating the overactive thyroid can help decrease the amount of ocular involvement, however, it will not resolve any active eye signs or symptoms of thyroid eye disease. Medications are available to decrease the production of thyroid hormones. Radiation and thyroidectomy (partial or full removal of the thyroid) are other options to treat hyperthyroidism. It is also possible that the thyroid hormone levels become too low after treatment, which is called hypothyroidism. This may need to be treated with oral medications to increase and stabilize thyroid levels.
The treatment for dry eye syndrome associated with thyroid eye disease consists of artificial tears, gel, and ointment. If the eyelids do not shut fully, taping the eyelids closed while sleeping is necessary for some individuals to prevent permanent damage from corneal scarring.
Double vision can be treated with glasses that have prism in the lenses or temporarily patching an eye. In some cases, the double vision does not fully resolve after the inflammation is treated. Surgery to realign the eye muscles and debulk the orbital cavity is an option for some individuals.
The most serious complications arise when the optic nerve is compromised. Optic neuropathy is caused by prolonged compression and damage to the optic nerve tissue. Surgical decompression is a complex treatment option to relieve pressure off the nerve and hopefully preserve vision. Oral and intravenous steroids are occasionally needed to decrease inflammation in these severe cases.
How do you prevent thyroid eye disease?
Once diagnosed with a thyroid condition or Graves’ disease, it is important to have regular eye exams to monitor for any changes that could be associated with thyroid eye disease. Controlling thyroid hormone levels can help minimize the chance of ocular involvement. An endocrinologist is a specialist that treats conditions related to the thyroid. A CT scan can be useful in detecting changes to the eye muscles, surrounding tissues, and optic nerve.
