The thyroid gland is a butterfly-shaped gland present in the front of the neck and secretes the thyroxin hormone, which is responsible for maintenance of the normal metabolic activities of the human body. But when present in abnormally high quantities it can cause various adverse side effects as a result of the increased rate of metabolism.
Paradoxically the thyroid gland and the muscles, which move the eyes (extra-ocular muscles), share a common antigen and the antibodies that attack the thyroid gland also attack the extra-ocular muscles resulting in swelling of the muscles and the surrounding fat tissues. As the bony orbit that encases the eye cannot expand to accommodate the sudden increase in volume, the eye is pushed forward giving the affected person a “staring look”.
Changes in the eye
This condition in which the eyes are affected by the underlying thyroid condition is called Thyroid Related Ophthalmopathy (TRO) or Graves Ophthalmopathy. Usually the patient presents with eye changes first following which the underlying hyperthyroid condition is diagnosed. The eyes usually become red (congested) and irritable and the patient feels a sense of tightness behind the eyes. The eyes become prominent (Proptosis) and the lids are puffed up. If the condition is left untreated it can result in the patient experiencing double vision (Diplopia); in rare cases, the enlarged muscles press on the optic nerve, which takes the visual impulses from the eye to the brain, and can result in blindness.
The first step in managing this condition lies in performing appropriate blood investigations to detect levels of circulating thyroid hormones and presence of anti-thyroid antibodies. A routine eye examination to check vision, colour vision, field of vision and eye pressure and extra-ocular movements is done. Imaging studies like ultrasound or CT scan may also be required to find out whether the eye muscles are enlarged.
The patient should be managed medically by the endocrinologist using drugs to reduce the thyroid hormone levels and inflammation. Smoking and high stress levels increase the intensity and so patients are advised to abstain from smoking and undertake stress management courses.
Management of TRO first involves applying lubricating eye drops (artificial tears) and ointment to keep the eye moist. Also sleeping with the head elevated with an extra pillow at bedtime helps decrease the early morning puffiness around the eyes.
The staring look (lid retraction) usually improves once the condition is under control. Long standing cases, which do not improve, can be corrected with surgery to bring the lids back to its normal position (Lid repositioning).
Diplopia also improves if the condition is treated early; late stages may require surgery to readjust the position of the eye muscles (squint surgery) and special glasses with prisms.
Long-standing untreated cases result in a cosmetically unacceptable appearance with huge, bulgy eyes (proptosis). Surgery can be done but will involve removing bone from the surrounding orbital walls (orbital decompression surgery) to create more space for the extra tissues and will result in the eye going back into the socket.
Rare cases
In rare situations, orbital decompression surgery will have to be done on an emergency basis if there is risk to vision due to optic nerve compression and can help salvage vision if done at the appropriate time. This is quite complex and should be done only by surgeons who have sufficient expertise and training.
TRO is a debilitating condition that can result in psychological difficulties like loss of self-esteem or self-confidence due to changes in the facial appearance. Early diagnosis and appropriate therapy jointly by an ophthalmologist and endocrinologist will help prevent many of the disabling long-term side-effects.
Thyroid Gland
The thyroid is a small (25 gm) butterfly-shaped gland at the base of the throat. The largest of the endocrine glands, it consists of two lobes joined by the isthmus. It is composed of many functional units called follicles, which are separated by connective tissue.
It is one of the vital endocrine glands and the hormones it secretes control metabolic pathways and thereby various physiological functions. The gland operates in concert with the hypothalamus and the pituitary, commonly referred to as the “hypothalamic-pituitary-thyroid axis”. The thyroid is stimulated by the pituitary hormone Thyroid stimulating hormone TSH to produce two hormones, thyroxine (T4) and triiodothyronine (T3), in the presence of iodide.
The writers are Chennai-based ophthalmologists.
