THYROID EYE DISEASEOphthalmologist Carolina Valdivia, MD explains thyroid eye disease: its symptoms, risk factors, and options for treatment. Thyroid eye disease (TED) is an autoimmune inflammatory disorder affecting the orbit of the eye. Although separate from thyroid disease, it is more common in Graves disease and other thyroid patients. TED also is known by several other names. Among them are Graves ophthalmopathy, thyroid-associated orbitopathy (TAO), and Graves orbitopathy.
The autoantibodies target the cells in the eye muscles called fibroblasts. These cells are the primary components of connective tissue and play a major role in wound healing. Fibroblasts attacked by autoantibodies can differentiate into fat cells (
adipocytes
). Fat cells and muscles expand and become inflamed. Veins become compressed, and are unable to drain fluid, causing swelling (edema). Who Gets Thyroid Eye Disease?In 1835, Robert James Graves was the first to describe the association of a thyroid goitre with another condition known as exophthalmos of the eye. Exophthalmos is characterized by an anterior bulging of the eye out of the orbit. The condition can involve both eyes (as is often observed in Graves disease) or only one eye (as is typical for an orbital tumor). Thyroid Eye Disease can occur before, during, or after the onset of overt thyroid disease and most often has a slow development over many months. TED typically affects persons 30-50 years of age. Of patients with Graves hyperthyroidism, 20-25% have clinically obvious TED, while only 3-5% will develop severe ophthalmopathy. Cigarette smoking, which is associated with many autoimmune diseases, raises the incidence of thyroid eye disease nearly 8-fold.
CLINICAL CHARACTERISTICS OF THYROID EYE DISEASETED is an orbital autoimmune disease. The primary target for autoantibodies appears to be the thyroid stimulating hormone receptor (TSH-R), a protein found in orbital fat and connective tissue. However, some patients with TED do not present with the antibodies identified in Graves disease, including anti-TSH-R. In TED, inflammation occurs because the orbital connective tissue is infiltrated by cells associated with an immune response, such as plasmocytes, lymphocytes, and mastocytes. The inflammation results in the inappropriate deposition of collagen and glycosaminoglycans* in the muscles, which leads to subsequent enlargement and fibrosis**. There also is a simultaneous induction of lipogenesis (fat production), which causes an enlargement of orbital volume.* Glycosaminoglaycans (GAG) are complex carbohydrates that are key components in synovial fluid, which lubricates body joints, and chondroitins that are found in connective tissues, cartilage, and tendons.** Fibrosis is the formation or development of excess fibrous connective tissue in an organ or tissue as a reparative or reactive process (e.g. scar tissue), in contrast to a formation of fibrous tissue as a normal constituent of an organ or tissue.SIGNS AND SYMPTOMS OF TED
Upper eyelid retraction is the most common ocular sign of TED. This finding is associated with a lag of the upper eyelid when looking downward (infraduction) known as Von Graefe's sign, a lag of the eyeball rotation upon looking upward (supraduction) known as Kocher's sign, a widened longitudinal opening between the eyelids (palpebral fissure) during fixation known as Dalrymple's sign, and an incapacity of closing the eyelids completely (lagophthalmos). Exophthalmos, eyelid retraction, and lagophthalmos make the cornea of the eye more susceptible to dryness, which may lead to swelling of the conjunctiva (chemosis), a breakdown or damage of the cells lining the surface of the cornea in a pinpoint pattern (punctate epithelial erosions), and inflammation of the conjuntiva and edges of the cornea in the upper half of the eye (superior limbic keratoconjunctivitis). Impaired function of the lacrimal gland is common, with a decrease of the quantity and quality of tears produced. Other symptoms experienced to varying degrees include eye irritation and grittiness, sensitivity to light (photophobia), swelling of tissues around the eyes (periorbital edema), and blurred vision. Patients usually do not report experiencing pain in the early stages, but often complain of feeling pressure in the orbit. Swelling around the orbit of the eye (periorbital edema) caused by inflammation also may be present. Symptoms are persistent and increasing as the disease progresses. Muscle weakness (thyrotoxic myopathy) in the eyes, face, throat, neck area, shoulders and hips can be present. Inflammation and edema of the extraocular muscles often lead to gaze abnormalities, such as strabismus. The inferior rectus muscle is the most commonly affected muscle and patients may experience intermittent vertical diplopia (double vision) upon gazing upward that gradually can become chronic. The actual ability to elevate the eyes may be limited due to fibrosis of the inferior rectus muscle. The medial rectus is the second-most commonly affected muscle. However, multiple muscles may be impacted, in unpredictable ways. Increases in intraocular pressure also may be observed at this point. Acute instances of TED present with a progressive exophthalmos, a restrictive myopathy that restricts eye movements, and an optic neuropathy. The
optic nerve
is at risk for damage due to enlargement of the extraocular muscle at the orbital apex (back of the eye), orbital fat deposition, or stretching of the nerve due to increased orbital volume. A loss of visual acuity,
visual field defects,
relative afferent pupillary defect, and loss of color vision may also be present. Acute TED constitutes a medical emergency and requires immediate surgery to prevent permanent blindness.
RISK FACTORS FOR THYROID EYE DISEASEThe following factors have been associated with elevated risk for progressive and severe TED.
The single most important thing that you can do to prevent thyroid eye disease or to control symptoms after its onset is to stop smoking. Tobacco smoke contains substances that affect thyroid function. Smokers are more likely to have thyroid enlargement. Moreover, smokers are twice as likely as nonsmokers to develop Graves disease and smoking significantly worsens the symptoms of TED.
TREATMENT OPTIONS FOR THYROID EYE DISEASESome patients experience spontaneous remission of their symptoms within a year. However, many require treatment. The first priority is for an endocrinologist to regulate thyroid hormone levels. This can significantly slow or halt the progression of TED symptoms. However, those already present still will require treatment.Corneal damage caused by exposure and reduced tear production. In mild cases, this can be be controlled through the use of eye drops. In extreme cases, tarsorrhaphy may be required. Tarsorrhaphy is a surgical procedure in which the eyelids are partially sewn together to narrow the eye opening (palpebral fissure). This option sometimes is necessary when eye drops alone prove insufficient to control the complications of ocular exposure. Orbital inflammation. Corticosteroids are effective in temporarily reducing orbital inflammation. However, the use corticosteroid treatment is limited by its many side effects, including raising intraocular pressure. Radiation therapy is an alternative option to reduce acute orbital inflammation, but there is some controversy surrounding its use and effectiveness. Recent reports indicate that rituximab, (brand names Rituxan and MabThera), a drug currently used in the treatment of some leukemias and lymphomas, shows promise in treating thyroid eye disease. Thus far, patients have not reported adverse side effects associated with its administration and significant improvement has been observed as early as one month following treatment. However, additional studies are needed to demonstrate the efficacy of rituximab in treating TED. Orbital decompression. Surgery may be conducted to decompress the orbit, to improve exophthalmos and to address the strabismus causing diplopia. A patient is considered a candidate for surgery if their disease has been stable for six months or more. The exception to this guideline is acute cases, in which urgent surgery is necessary to prevent blindness from optic nerve compression. The eye orbit is comprised of six major bones. Because the orbit is inflexible, it cannot adjust to accommodate eye muscle swelling and inflammation associated with TED. Consequently, the eyeball is pushed forward into a protruded position (exopthalmos). This can be very pronounced in some patients. Orbitial decompression consists of removal of some bone from the orbit to make space for the swollen tissue and to allow the eye to move back into a more normal position. This procedure also can relieve optic nerve compression and thereby reduce the risk of vision loss.
Fibrosis of the upper eyelid muscle (levator palpebrae superioris) reduces its effectiveness and contributes to a widened longitudinal opening between the eyelids (palpebral fissure) and an incapacity of closing the eyelids completely (lagophthalmos). A surgical procedure known as marginal myotomy can reduce the palpebral fissure height by 2-3 millimeters. This technique involves making two small incisions directly opposite each other at the margins of the levator palpebrae superioris. This exposes internal muscle tissue that is unaffected by fibrosis and allows the levator palebrae superioris to stretch. When upper eyelid retraction is severe, a second procedure known as lateral tarsal canthoplasty is recommended along with marginal myotomy. This can lower the upper eyelid by as much as 8 millimeters. Another procedure called blepharoplasty can remove excess fat from the lower eyelid.
REFERENCE:Dutton JJ and Haik BG. Thyroid Eye Disease: Diagnosis and Treatment. New York: Marcel Dekker, 2002:1-471.
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