Progression of Thyroid Eye Disease
When the immune system attacks the muscles and other ocular tissues in the eye socket, the swelling and scarring resulting from the inflammation can cause the symptoms and signs noted above. In severe cases, the transparent window of the eye (cornea) may become overly exposed and dry, leading to ulceration, or the optic nerve may be damaged from compression by scarred muscles or by stretching from eye protrusion. Either of these devastating complications may result in a permanent loss of vision if not treated appropriately. Corneal damage is often due to a combination of the eyes bulging forward and eyelid retraction from eyelid tissue scarring, leading to exposure of the cornea from poor lid closure (see below). Optic nerve damage is due to thickened, inflamed and/or scarred muscles impinging on the optic nerve at the back of the socket (apex), just as the nerve exits the orbit to enter the brain (see below).
In most patients who develop thyroid eye disease (also known as Graves’ ophthalmopathy), the eyes bulge forward and/or the eyelids retracts to some degree. Many patients with mild thyroid eye disease will experience spontaneous improvement over the course of two to three years, once the thyroid endocrine disease is treated. Many patients also adapt to the abnormality and learn to compensate. Severe ophthalmopathy usually affects approximately 10% of patients. It is caused by inflammation of the muscles and orbital fat, which causes them to swell. As they swell, the muscles and fat can scar in the swollen state, push the eye forward, stretch the optic nerve, and press on the nerve in the orbital apex. Pressure or stretching of the nerve can cause permanent vision loss. Scarring of the muscles can also lead to double vision because the muscles can no longer work well together. In some patients, eye protrusion makes it difficult for the lids to close properly and the cornea becomes exposed and vulnerable. Rarely, orbital swelling may precipitate glaucoma that can also affect the optic nerve. Surgical intervention is often required in order to save or restore adequate visual function.