TED is an autoimmune condition where the body’ own immune system attacks the tissues of the thyroid gland and the eye socket. Inflammation of the tissues in the eye socket causes the signs of TED, but the reason for the inflammation (not infection) is not fully understood. Inflamed tissues around and behind the eye become swollen and congested causing proptosis and sore/red eyes can result from the eyelids not closing fully. Swelling of the eye muscles reduces their ability to contract and relax thereby affecting eye movements. If the muscles get very swollen, they can compress the optic nerve at the back of the eye socket causing the vision to drop.