Thyroid - Related Eye Disease
- Hyperthyroidism almost always causes general eye symptoms like dryness and irritation, regardless of what the cause of the hyperthyroid state is. However, these need to be distuingished from Graves' ophthalmopathy, which can only occur in patients who have Graves' disease. (It could also, rarely, be seen in Hashimoto's thyroiditis, primary hypothyroidism, and thyroid cancer).
- About 20-25% of patients with Graves' disease will suffer from clinically obvious Graves' ophthalmopathy, and not just from the eye signs of hyperthyroidism. Only 3 to 5% will develop severe ophthalmopathy. However, when subjected to closer inspection (e.g. by magnetic resonance imaging of the orbits) several more patients have evidence of ophthalmopathy (primarily enlargement of retroocular muscles). It is estimated that for every 100,000 persons, 16 women and 3 men have Graves' ophthalmopathy every year.
- Although it is true that in most patients ophthalmopathy, goiter, and symptoms of thyrotoxicosis appear more or less coincidentally, it is also true that in certain cases eye signs could appear long before thyrotoxicosis is evident, or become worse when the thyrotoxicosis is subsiding or has been controlled by treatment. In approximately 20% of ophthalmopathy patients, ophthalmopathy appears before the onset of hyperthyroidism, in about 40% concurrently, and in about 20% in the six months after diagnosis. In the remainder, the eye disease initially becomes apparent after treatment of the hyperthyroidism, more often in patients treated with radioiodine.
- It can often be difficult to distinguish between eye symptoms due to hyperthyroidism and those due to Graves' antibodies, not in the least because the two often occur coincidently. What can make things particularly difficult, is that several patients with hyperthyroidism have lid retraction, which leads to stare and lid lag (due to contraction of the levator palpebrae muscles of the eyelids). This stare could then give the appearance of protruding eyeballs (proptosis), when none in fact exists. This subsides when the hyperthyroidism is treated.
Graves' ophthalmopathy is characterized by inflammation of the extraocular muscles, orbital fat and connective tissue. It results in the following symptoms, which can be extremely distressing to the patient:
- Most frequent are symptoms due to conjunctival or corneal irritation: burning, photophobia, tearing, pain, and a gritty or sandy sensation.
- Protruding eyeballs (known as proptosis and exophthalmos).
- Diplopia (double vision) is common.
- Limitation of eye movement (due to impairment of eye muscle function).
- Periorbital and conjunctival edema (accumulation of fluid beneath the skin around the eyes).
- Infiltrative dermopathy (pretibial myxedema).
- In severe cases, the optic nerve could be compressed and acuity of vision impaired.
- Occasionally loss of vision.
Due to hyperthyroidism
In the absence of Graves' ophthalmopathy, patients could demonstrate other ophthalmic signs due to hyperthyroidism:
- Dry eyes (due to loss of corneal moisture).
- A sense of irritation, discomfort, or pain in the eyes.
- A tingling sensation behind the eyes or the feeling of grit or sand in the eyes.
- Excessive tearing that is often made worse by exposure to cold air, wind, or bright lights.
- Swelling or redness of the eyes.
- Lid lag (Von Graefe's sign)
- Sensitivity to light.
- Blurring of vision.
- Widened palpebral fissures.
- Infrequent blinking.
- The appearance of lid retraction.