Thyroid Disease Can Blind
The thyroid is a large gland located in the neck. Its main purpose is to produce thyroxin, a hormone which regulates our metabolism. If the thyroid produces too much thyroxin, hyperthyroidism will occur. A reduced level of thyroid hormone produces hypothyroidism. Unfortunately, both conditions can affect vision and cause eye problems.
The symptoms of hyperthyroidism include a fast heartbeat, weight loss, fatigue, heat intolerance, and diarrhea. An underactive thyroid can also cause fatigue, but usually with a slow heartbeat, weight gain and constipation.
Early symptoms of thyroid related eye disease (TRED, sometimes referred to as Grave's Disease) include puffiness (edema) of the tissues surrounding the eyes, especially the lower lids, along with dry eyes and a staring appearance. SweIling of the normal fatty tissue surrounding the eyeball can push the eye forward creating a prominence or protrusion of the eye. The degree of protrusion is variable and may involve one or both eyes. Swelling of the muscles which move the eye may produce double vision. When the eyes protrude significantly, the clear cornea of the eye can become severely dry and break down. In some cases, the optic nerve may become compressed, resulting in a permanent loss of vision.
It is interesting that a person can have TRED even though routine thyroid function tests are normal. The reason for this is not well understood, but may relate to an immune system abnormality which affects both the thyroid and the ocular tissues. However, most patients with eye symptoms have abnormal thyroid hormone levels.
The treatment of TRED can be difficult and challenging. If a thyroid abnormality is suspected, proper medical treatment can usually restore normal thyroid hormone levels. Unfortunately, the eye disease may continue to progress even though the thyroid abnormality is corrected. It has been well documented that smoking can make thyroid eye disease worse. So this is a factor that must seriously be considered in patients with this condition.
Usually treatment consists of two phases. The first phase involves treating the active eye disease, with treatment focused on preserving the patient's sight. Sometimes surgery is required to achieve this goal. The active phase can last two to three years before the ocular changes stabilize. Once stabilized, the second phase begins. This involves correcting the permanent ocular changes including the ocular protrusion, the staring appearance of the eyes and double vision.
The prognosis for patients with TRED is excellent. Early diagnosis, with the cooperative efforts of the internist and the ophthalmologist, can prevent permanent visual loss and reduce both the physical and psychological scarring.
