The most common cause of thyroid eye disease is Graves’ disease, an autoimmune disorder which mostly affects women of childbearing age. Other causes of hyperthyroidism, with less tendency to affect the eyes, include multinodular goitre, subacute thyroiditis and excessive thyroid hormone medication.
Thyroid eye disease in the context of Graves’ disease is termed thyroid-associated ophthalmopathy (TAO). It generally progresses independently of thyroid hormone levels, and occasionally occurs with normal thyroid function. Ocular changes may include:
- Acute inflammation: of the conjunctiva, lacrimal gland and other periorbital tissues
- Proptosis (exophthalmos): due to chronic inflammation within the orbit and extraocular muscles. Eyelid retraction occurs in approximately half of patients with Graves’ disease, due to a combination of increased sympathetic activity, proptosis and fibrosis.
- Ocular motility is restricted by edema in the acute phase, and later by fibrosis, resulting in diplopia.
- Optic nerve compression by enlarged extraocular muscles at the orbital apex is a serious complication affecting 5 percent of patients with TAO. Compression of the optic nerve within 15mm of the globe may compress the venous outflow, leading to optic disc swelling.
Ocular involvement is often asymmetrical. The eyes are swollen and red in the acute phase, with discomfort and possible blurred vision in severe cases. Diplopia occurs with exophthalmos and ocular motility disturbance. Optic nerve compression causes progressive visual loss.
- Proptosis (‘thyroid stare’) may be measured with an exophthalmometer. Lid retraction is measured as visible sclera between the limbus and eyelid margins. With lid lag, there is delay of the upper lid in following downward rotation of the globe in downward gaze.
- Limitation of eye movements
- Corneal exposure: superficial punctate keratitis, ulceration or necrosis.
- Optic nerve compression may cause relative afferent pupillary defect, reduced central acuity, and color vision or visual field defects. Fundoscopy may reveal disc swelling with congested retinal veins in acute compression, and a pale, atrophic optic disc in longstanding cases. However, the fundus appears normal in up to half of patients, when the optic nerve compression is more than 15mm from the globe.
TAO is the most common cause of proptosis in adults.
Corneal exposure and optic nerve compression are preventable causes of severe visual impairment.
Orbital Inflammatory Pseudotumour, Orbital Cellulitis, Orbital Tumors, Orbital Trauma
Thyroid function tests are performed during diagnosis and monitoring. Anti-TSH (thyroid-stimulating hormone) antibodies are detectable in almost all cases of Graves’ disease. Orbital computed tomography (CT) or magnetic resonance imaging (MRI) demonstrate thickening of extraocular muscles, and may help differentiate active inflammation from fibrosis.
Ocular lubricants and artificial tears may relieve conjunctival or corneal irritation.
In more severe cases, and in cases of optic nerve compression, oral corticosteroids (often prednisolone) may be used. Other immunosuppressives, radiotherapy and/or surgical decompression may be considered. Although systemic hyperthyroidism will require treatment on its own merits, lid retraction is the only ocular manifestation likely to respond.
Diplopia may be temporarily relieved by prisms or, in severe cases, occlusion.
- Proptosis and diplopia. Surgery for proptosis entails removal of part of two or more orbital walls, allowing the orbital contents to prolapse into the surrounding sinuses. Surgery is considered when the inflammation has resolved and the diplopia has been stable for several months. Loosening (recession) of a fibrosed inferior rectus muscle is a common procedure.
- Lid retraction. Lid position surgery for exposure keratopathy or cosmetic reasons is best performed subsequent to any orbital or eye muscle surgery.
Disc swelling with flame-shaped haemorrhages from compression of the optic nerve. Visual failure usually occurs without disc swelling unless within 15mm of optic nerve head.
Same patient: CT scan showing grossly enlarged medial rectus muscles impinging on the optic nerve.