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Thyroid-associated Eye Disease

DR. R.A. Bell, MD
Queen's University, Kingston, Ontario

Many terms have been proposed to describe the ocular complications associated with thyroid dysfunction. A relatively simple and descriptive term is "Thyroid-Associated Eye Disease". This encompasses a collection of signs and symptoms which individually are non-specific, but collectively are very characteristic.

TAED has a loose association with thyroid dysfunction and may occur a) before thyroid dysfunction, b) concomitantly with hyperthyroidism or hypothyroidism, or c) after treatment of thyroid disease either immediately or delayed.

The etiology of TAED remains unknown. It is apparent that the thyroid dysfunction and the eye disease probably have a similar etiology but the thyroid dysfunction does not cause the eye disease per se. The ocular manifestations are due to increased fluid and inflammatory cells within the orbital tissues leading to compression and scarring of ocular structures. The cause of this accumulation of fluid and inflammatory cells is thought to be due to an immunological structures. However, this theory has not been proven.

The incidence of TAED in patients with thyroid dysfunction varies from 40 to 90 per cent overall. However, serious ocular problems occur in only 5 per cent or less of patients.

Several generalities can be made regarding the course, duration and severity of TAED. Firstly, it is extremely unpredictable and, therefore, it is virtually impossible to predict at the onset of the disease what the eventual outcome will be. Secondly, TAED in most cases is unrelated to the course of the thyroid disease and good control of the thyroid disease does not necessarily prevent TAED. In some cases, TAED may even occur after the thyroid disease has been controlled. Thirdly, the onset of TAED is usually slow over a period of months but it can be rapid or extremely slow. Fourthly, the disease is usually bilateral but often asymmetric (one eye affected more than the other). Lastly, the activity usually runs from 6 months to 3 years but once activity has ceased, reoccurrence is extremely rare. Complete recovery is infrequent but often there is good to excellent improvement in both signs and symptoms.

Staging of TAED is helpful for research purposes but it is not particularly useful for patient understanding of what is happening. It is more meaningful to describe the condition as mild, moderate, or severe and to describe the state of the ocular structures involved. The following is a description of ocular complications that may occur in TAED. They may occur separately or in combination. Contrary to popular belief, glaucoma is not a manifestation of TAED.

None
It is important to remember that not everyone with thyroid disease will have TAED. It is also equally important to understand that patients with thyroid disease may have other eye diseases which in some cases may mimic TAED. It is, therefore, important that patients with eye problems have an ophthalmological check up. In the majority of cases, a correct diagnosis can be made.

Lid Retraction
This is a condition in which the upper eyelid is retracted upwards, exposing a greater area of the eye. This may create the appearance of anger, staring, daydreaming, etc., and may also create the appearance of large prominent eyes. Unless the patient is aware of what is happening, he or she may be subjected to various untrue and non-complimentary remarks.

Lid Retraction may cause slight drying and irritation of the eye but rarely leads to serious problems. Glasses are often helpful both from a cosmetic and a protective standpoint. Carefully chosen glasses often diminish the prominent eye appearance as well as provide protection from dust, wind, etc. Eye drops such as Guanethidine which paralyze the muscle of the upper lid and allow it to cover a greater part of the eye have been suggested by suggested by some. However, the drops are absorbed systemically and may have serious side effects and are not encouraged. Surgical procedures which weaken the muscle of the upper lid thereby allowing the lid to rest in a more normal position are often successful.

Poor Lid Closure
This is a condition in which the eyelids do not completely close and allow exposure of the cornea. This may result in drying of the eye causing redness, irritation, and photophobia (sensitivity to light). Patients with this problem may also be accused of "sleeping with their eyes open".

In the majority of cases, poor lid closure does not result in serious complications and the drying of the eye can be controlled with lubricating eye drops. However, in severe cases, systemic medications, surgery, and/or radiotherapy may be necessary (these will be discussed later).

Tissue Swelling
This is a condition in which fluid accumulates in the eyelids and "white part" of the eye resulting in redness, puffiness, photophobia, irritation, and tearing of the eye. Patients may be accused of "keeping late nights" when in fact this is not the case.

In most cases, tissue swelling does not lead to major ocular complications, and often sleeping with the head of the bed elevated decreases the excess accumulation of fluids. Again, glasses are often helpful in preventing exposure to dust, wind, etc., and in creating a cosmetic improvement. Lubricating eye drops are helpful in relieving the irritation. In severe cases, systemic medications, surgery, and/or radiotherapy may be used.

Proptosis
Proptosis or exophthalmos is a condition in which the eyes are pushed forward due to accumulation of fluid and cells within the orbit and behind the eyes. This creates the appearance of large prominent eyes and, depending upon the degree of forward displacement, may result in drying of the eye causing redness, irritation, photophobia and blurred vision.

Mild proptosis usually does not lead to complications. Treatment with glasses and lubricating drops is often successful. In severe cases, systemic medications, surgery, and radiotherapy may be necessary.

Corneal Problems
The cornea is the "clear window" at the front of the eye and is extremely important for vision. Exposure of the cornea results in drying, causing irritation, photophobia, tearing, pain, and in some cases, decreased vision.

The severity of corneal exposure depends upon a combination of poor lid closure, lid retraction and proptosis. In mild cases, lubricating eye drops are successful in preventing any complications. In more severe cases, such as when ulceration occurs, systemic medications, surgery and/or radiotherapy may be necessary to prevent permanent damage.

Ophthalmoplegia
This is a condition in which the eye muscles become thickened and scarred, preventing the eyes from moving freely and/or together. It may result in "crossed eyes", double vision or blurred vision.

Unless straight ahead or down vision are affected, ophthalmoplegia usually does not require treatment. If these positions are affected however, glasses with prisms may eliminate the double vision in mild cases. In more severe cases, systemic medications, surgery and/or radiotherapy may be used. However, in the majority of cases, severe ophthalmoplegia can be helped only with surgical procedures which either weaken or strengthen various muscles allowing the eyes to work together again.

Optic Neuropathy
This is a condition in which the optic nerve is compressed by swollen structures in the orbit leading to poor central and side vision.

This is a serious complication and requires aggressive treatment such as systemic medications, surgery, and/or radiotherapy. In the majority of cases, if detected early, serious impairment to vision can be prevented.

Treatment
Treatment is aimed at providing comfort for the eyes and preventing serious complications. Although there is no treatment which cures the disease, permanent impairment to vision can usually be prevented. Treatment can be divided into two groups, minor and major.

Minor
Minor treatment includes the use of glasses, warm compresses, elevation of the head of the bed, and lubricating eye drops. Glasses often provide a cosmetic improvement and they also protect the exposed eye from dust, wind, etc. Warm compresses provide excellent symptomatic relief in many cases. Elevating the head of the bed often decreases the accumulation of fluid within, and around, the eyes. Lubricating eye drops are extremely helpful in preventing drying of the eyes.

Major
There are three main categories of major treatment; a) systemic medications such as steroids, Cyclophosphamide; b) surgery; c) radiotherapy. The general indication for major treatment is any condition which may lead to permanent damage to vision. In most cases of TAED, however, permanent decrease in vision does not occur and, therefore, these forms of treatment are often not necessary.

Drugs such as steroids and cyclophosphamide have an anti-inflammatory effect which causes a decrease in swelling of the ocular tissues, allowing the eye to retract back into the orbit.

The various surgical techniques include weakening of the upper eyelid, weakening and/or strengthening of the eye muscles and removal of excess tissue from behind the eye.

Radiotherapy causes a decrease in the swelling of the ocular tissues similar to the systemic drugs.

All three forms of major treatment have their advantages and disadvantages and it is difficult to list one as being superior. In all cases, the patients should be informed of the various forms of treatment, their advantages and disadvantages and their complications. Other illness - both past and present - must be taken into consideration when considering these forms of treatment. In some cases, a second opinion is often reassuring to the patient and if requested in a friendly and open manner, is constructive for both the patient and physician.

Summary
In conclusion, several important points can be made regarding TAED.

  1. Many patients with thyroid disease have associated eye problems but in the majority of cases, it is not severe.
  2. TAED can occur before, during, or after the thyroid problem.
  3. The course, duration, and severity of TAED is extremely unpredictable but it usually runs from 6 months to 3 years. Once remission occurs, it is extremely rare to re-occur.
  4. Complete recovery is infrequent but often this is good to excellent improvement.
  5. In the majority of cases, treatment is successful in preventing serious damage to the eye.

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Reviewed 2000