Graves disease is an autoimmune disease.  This means that the immune system, the white blood cells, are attacking your own body.  You may have heard of other diseases where the immune system attacks the patient's own body.  In Rheumatoid Arthritis, the white blood cells attack the joints.  In Lupus, they attack the lungs.  In the commonest type of Graves disease, the white blood cells attack the thyroid gland, releasing thyroid hormone.  Testing the blood for the level of thyroid hormone confirms the diagnosis.  This hormone affects many systems of the body.

In a small percentage of patients with Graves disease, the white blood cells also attack the fat and muscles behind the eyes, causing

inflammation of and around the eye

swelling of the upper and lower eyelids

pain around the eyes

sometimes double vision

rarely, loss of vision. 

The inflammation usually lasts from six months to two years.  The attack on the tissues behind the eye can happen before the thyroid is attacked, at the same time, or later.  In most patients with Graves disease the immune system, white blood cells, attack only the thyroid and not the eyes.  Graves eye disease is much more common in people who smoke. In some patients the attack can be on the tissues behind the eye and not on the thyroid gland, so that the thyroid blood tests are negative.  In that case, the diagnosis is made by seeing enlarged muscles behind the eyes on the CAT scan (a kind of x-ray), and sometimes by a special blood test for chemicals (antibodies) attacking the thyroid.

When Graves disease affects the eyes, several problems can occur: 

The inflammation can result in redness of the eye and pain and pressure around the eyes.  If it is mild, this can be treated with medications like Advil.  In more severe cases, prednisone pills are used.

The eyelids can open too widely, and this interferes with the way the eyelids blink and lubricate the eyes, resulting in irritation of the surface of the eyes and discomfort.  This is treated initially by using lubricating eye drops.  After the disease has stabilized, the eyelids can be placed back into their normal position by surgery.

When the muscles are swollen they cannot move the eyes smoothly, and if the two eyes do not move together, then double vision can result.  This can be treated by special glasses or surgery.

If the swelling behind the eyes is severe, the eyes can be pushed forward in the socket (orbit).  The pressure behind the eyes can damage the optic nerve, which carries the image from the eye to the brain, decreasing the vision.  The first treatment is with prednisone pills. Some patients require surgery, which opens the bones around the orbit to allow more room for the swollen muscles, relieves the pressure on the optic nerve, and allows the eye to move back into the orbit.

The eye symptoms of Graves disease can be quite distressing and can last for some time. Once the disease has stopped evolving, corrective surgery can generally improve the comfort, eliminate the double vision, and even  improve the appearance of the eyes.