Thyroid eye disease (thyroid orbitopathy or TO) is a condition that causes the muscles and soft tissues of the eye socket to swell. It happens when you have a problem with your thyroid gland. You may also hear it being called Graves’ disease. The condition is characterised by a period of inflammation and swelling of these tissues, followed by a healing response.

The condition most commonly occurs in association with an overactive thyroid gland, but can also occur if you have an underactive thyroid gland; an identical picture sometimes occurs when the thyroid gland itself is not affected.

Autoimmune disease and the thyroid

The main problem affecting the thyroid is autoimmune disease. Our immune system normally makes small proteins (antibodies) to attack bacteria and other ‘germs’ that are foreign to us. If you have an autoimmune condition, your immune system makes antibodies to act against normal tissues of your body. At the moment the reason for this is not entirely clear. Thyroid cancers can also occur.

Why thyroid problems affect the eyes

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

How thyroid disease affects the eyes

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

Some signs you may notice:

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

The law states that 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 the law requires you 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 then DVLA may declare you fit to drive again. Not informing the DVLA of double vision could invalidate your insurance and you would also be driving illegally.

In severe thyroid eye disease, 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. Your optic nerve carries the messages from your eye to your brain and can be damaged by pressure.

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