Thyroid eye disease

Thyroid eye disease (thyroid orbitopathy or TO) is a condition of inflammation and engorgement of the soft tissues surrounding the eyes.

How the eye works

We need light to see what is around us and to see colour. Light bounces off the objects we look at. These reflect different amounts of light which we see as different colours.

Light rays enter the front of our eye through the clear cornea and lens. It is very important that both the cornea and lens are clear as this allows the light to pass directly through the front of the eye to the retina. The cornea and lens bends light so that it can focus on the retina at the back of our eye. This gives us a clear, precise image. The cornea focuses the light towards our retina. The lens fine tunes the focussing of this light

Our tears form a protective layer at the front of the eye and also help to direct the light coming into our eye. The iris, the coloured circle at the front of our eye, changes the size of the pupil which allows different amounts of light into our eye. The pupil is the dark hole in the middle of the coloured part of our eye. The pupil gets smaller in bright conditions to let less light in and gets bigger in dark conditions to let more light in.

The middle of our eye is filled with a jelly-like substance called the vitreous. The vitreous is clear and allows light to pass directly from the front to the back of our eye.

The retina at the back of the eye is a light-sensitive layer which consists of rod and cone cells. These cells collect the light signals directed onto them and send them as electrical signals to the optic nerve at the back of our eye.

Rod cells are concentrated around the edge of the retina. They help us to see things that aren't directly in front of us, giving us a rough idea of what is around us. They help us with our mobility and getting around by stopping us from bumping into things. They also enable us to see things in dim light and to see movement.

Cone cells are concentrated in the centre of our retina where the light is focused by the cornea and lens. This area is called the macula. Cone cells give us our detailed vision which we use when reading, watching TV, sewing and looking at people's faces. They are also responsible for most of our colour vision.

The optic nerve is made up of thousands of nerve fibres. These fibres pass the electrical signals along to our brain where they are processed into the image we are looking at.

Seeing can be likened to the process of taking pictures on a film with a camera which you then get developed. The retina is like a camera film which stores an image of what we are looking at. The image directed onto the retina is then sent along to the brain where it is processed, like developing a camera film. Therefore we actually 'see' in our brain with the light information sent to it from our eyes. This whole process happens very quickly so that everything we see is in focus.

About thyroid eye disease

Thyroid eye disease (thyroid orbitopathy or TO) is actually a condition of the soft tissues such as the fat and muscles surrounding the eyes. The condition is characterised by a period of inflammation and engorgement of these tissues, followed by a healing response.

The condition most commonly occurs in association with an overactive thyroid gland, but also occurs with an under active thyroid gland; an identical picture sometimes occurs when the thyroid gland is not itself affected.

Thyroid gland

The thyroid is one of the body's endocrine glands; these are glands which produce hormones. Hormones are chemical messengers in our blood streams, which co-ordinate long term changes in function. The thyroid is located in the neck just below the Adam's apple, and its hormones regulate our metabolism.

Diseases of thyroid

The main problem affecting the thyroid is auto-immune disease. Thyroid cancers also occur. The effect of thyroid disease is felt as either an over-activity or under-activity of the gland, and therefore either a speeding up or a slowing down of metabolism.

Auto-immune disease and the thyroid

Auto-immune problems are caused by inappropriate behaviour of the body's immune system. The immune system usually fights off infection but in auto-immune disease it attacks the body's own tissues with auto-antibodies. At the moment the reason for this is not entirely clear.

Why thyroid problems affect the eyes

When an auto-immune attack starts on the thyroid, it responds by producing more of its hormones. At the same time the auto-antibodies attacking the thyroid gland also attack the tissues around the eyes.

More information on thyroid problems is available from the British Thyroid Association, details at the end of this page.

How thyroid disease affects the eyes

The commonest problem is dry eyes. This is because, in auto-immune disease, more than one organ may be attacked, and commonly the thyroid and all the orbital contents (the soft tissues around the eye), including the lacrimal gland, are attacked by the immune system. The lacrimal gland produces the tears in our eyes, so when it is affected fewer tears are produced. As a result, the eyes may feel dry and gritty. It is worth noting that, although the eyes are described as 'dry', they can water and produce more tears than normal.

As the orbital contents (the soft tissues around the eye) become inflamed, all the tissues of the orbit become red and swollen.

  • The eyelids become puffy and red (lid swelling)
  • The muscles of the eyelids contract, producing a staring appearance (lid retraction)
    • The muscles and fat surrounding the eye swells, pushing the eyes forward so that they bulge out of the orbits (exophthalmos)
  • Lid retraction and exophthalmos make the dry eye symptoms worse.
  • The swelling of the muscles which move the eyes produces unequal movements and double vision (diplopia)
  • The orbits may become painful, particularly on eye movement.

How thyroid orbitopathy affects sight

If the muscles become swollen, then this can affect how well the muscles are able to control the ability of the eyes to move together. This can cause double vision. This is a symptom which occurs when the eyes do not quite point in the same direction and therefore each sends a slightly different message to the brain. When this happens our brains 'see' two of everything. This can make activities like reading very difficult, and driving very dangerous. If someone develops double vision then they must stop driving, it is illegal to drive with double vision which isn't controlled.

If you do develop double vision then you have to inform the Driver and Vehicle Licensing Authority (DVLA) and, usually, they will contact your ophthalmologist for a medical report. If your double vision then becomes controlled with glasses at a later date the DVLA will declare you fit to drive. Not informing the DVLA of double vision could have serious consequences for your insurance status and you would be also be driving illegally.

In severe Thyroid Orbitopathy, especially in younger patients whose firm tissues do not allow the eyes to bulge forwards, the pressure inside the orbits increases, compressing the optic nerve and causing sight problems. The optic nerve carries the messages from the eye to the brain and can be damaged by pressure.

If the pressure starts to compress the optic nerve sight may become dim, colours begin to look washed out, and the visual field may constrict. If this starts to happen, then medical attention needs to be sought as soon as possible, to reduce the pressure on the optic nerve before permanent damage occurs.

The treatment options for optic nerve compression are steroids, immunosuppressant drugs, orbital radiotherapy and emergency orbital decompression surgery. These all aim to lower the pressure on the optic nerve and hopefully avoid permanent damage.

Treatment for thyroid disease

The first priority is to deal with the primary thyroid problem. This is firstly with anti-thyroid drugs, and then with either surgery or radiotherapy. The treatment of an overactive thyroid often produces an under active thyroid, which then requires treatment with thyroid replacement therapy. It is very important to be aware that the treatment of the underlying thyroid condition often makes the associated eye condition worse, and to be ready for this.

Thyroid orbitopathy treatment

When the eyes are dry and gritty then the best treatment is to use lubricating eye drops - artificial tears.

These can help to make the eyes feel more comfortable and help to prevent the eye being damaged by being so dry.

Treatment for double vision

A variety of treatments are available depending on whether the double vision is temporary or permanent. An orthoptist (an eye professional who specialises in double vision) should be involved in such treatments.

Occlusion

In this treatment, one eye is simply covered up so that the brain receives only one image.

Prisms

Prisms work by bending light in a direction which compensates for the angle between the eyes. They can be tailored to the angle between the eyes and affixed to spectacles. Stick-on prisms, often called Fresnel prisms, are used until it is established that the angle is constant, at which point prisms, can be incorporated into the spectacle lens by an optometrist.

In temporary double vision during the active stage of TO, prisms may be the only treatment necessary. As TO burns out, however, it often leaves some residual double vision requiring surgical treatment.

Long term effect of thyroid orbitopathy

In the majority of cases, the active inflamed stage of TO burns itself out in about two years, leaving a variable amount of scarring, with lid retraction, exophthalmos or double vision.

A decision can then be made by the patient as to whether the problems that are left are acceptable, or whether they are severe enough to justify the risks of surgery.

If, after the thyroid orbitopathy has burned itself out, there are still problems with the eyes (including exophthalmos, lid retraction and double vision), then it becomes necessary to decide whether or not to have further surgery to help improve these things. Sometimes the problems that are left may only be minor and someone may feel it isn't necessary to have more treatment, or that the risks of the surgery outweigh the problems that they have. However, there may be cases where surgery is a more obvious choice.

If surgery is needed then it is carried out in the sequence of orbital decompression, surgery to the muscles of the eye for double vision, and surgery to correct the lid position.

Orbital decompression is carried out to place the eyes further back in the orbits where they belong. This is normally accomplished by removing a small amount of bone from inside the orbit of the eye so that the eye can sit further back in its socket. Occasionally fat may also be removed from the inside of the orbit. One of the major risks of this surgery is the development or worsening of double vision, so it should be expected that after this surgery someone may need muscle surgery as well. There is also a small risk of serious sight problems with this surgery.

If someone is left with stable permanent double vision, surgery is the treatment of choice to correct this. This surgery lengthens the muscles of the eye so that the eyes are brought back into alignment. This is usually done with an adjustable suture technique. Muscle surgery may alter the position of the eyelids and so it should be expected that at some point after muscle surgery, lid surgery may be necessary.

Lid surgery aims to correct the position of the upper and lower eyelids over the eyes, allowing proper closure.

To perform any of this surgery it is necessary for the thyroid disease itself to be stable and for the active phase of the orbital disease to have burnt out. Because of this some ophthalmologists believe that early low dose radiotherapy given early in the active phase of the TO can help improve the outcome after the TO has burnt out.

All this means that if someone is left with problems once the TO has burnt itself out then they could face a program of operations to improve vision. Usually the operations are performed in the following order: orbital decompression, surgery to the muscles for double vision and surgery to correct the lid position. Typically these operations are carried out over about 18 months to 2 years.

With modern surgical techniques, very few people are left to cope with the difficult after-effects of TO. The modern surgical techniques now aim to restore the position, function and appearance of the eyes to as near to normal as possible.

What next

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Useful contacts

Thyroid Eye Disease Charitable Trust (TEDct)
PO Box 1928
Bristol
BS37 0AX
Tel: 0844 800 8133
Email: ted@tedct.co.uk
Provides information, care and support to those affected by thyroid eye disease.

British Thyroid Foundation
PO Box 97
Clifford
Wetherby
West Yorkshire
LS23 6XD
Tel / Fax : 01423 709707
Aims to provide information and support for people with any kind of thyroid problems and their families.

Driver and Vehicle Licensing Agency (DVLA)
Drivers Medical Group
Longview Road
Moriston
Swansea
SA6 7UL
Can give advice on sight standards for driving.

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