Thyroid Eye Disease
The thyroid gland is a small gland that is located in the neck close to the Adam’s apple. It is responsible for the secretion of thyroid hormone. When the thyroid gland does not work the way it should, it can lead to several different symptoms.
One of the primary clinical problems associated with thyroid disease is eye disease. This is often seen when the gland is overactive i.e. in hyperthyroidism or Grave’s disease.
In Grave’s disease, there is development of ‘autoantibodies’ that are directed against the cells that are present in the thyroid gland. They can also interact with tissue behind the eye. Eye problems are seen in nearly 50% of people with Grave’s disease within 6 months of onset of symptoms.
Let’s take a brief look at the common eye problems seen with an overactive thyroid gland.
The primary problem that is seen with the eyes in Grave’s disease is the inflammation of fat and muscle tissue that is located behind the eye. Due to this, the eye is pushed forward, giving the appearance of larger than normal eyes. This is called exophthalmos.
The spectrum of eye problems seen with Grave’s disease is called Grave’s ophthalmopathy. However, it must be borne in mind that Hashimoto’s thyroiditis and thyroid cancer can sometime cause similar eye problems.
Some of the common problems associated with Grave’s ophthalmopathy include –
As the eye is bulged forwards, the upper eyelid fails to cover the entire eye to moisten it with secretions from the lacrimal gland. Due to this, the cornea, which is the part of the eye exposed to the surrounding atmosphere, can get dry.
A dry cornea can make blinking difficult and patients may experience a gritty sensation. This can lead to either completely dry eyes, or sometimes make the eyes water excessively as a protective mechanism.
A dry and exposed cornea also makes it prone to getting infected. Ulcers may form on the cornea which can sometimes be very painful and can lead to blurred vision.
With the expansion and inflammation of tissues at the back of the eye, the increased pressure that develops pushes the eyeball forward even further.
This can make the eye painful, especially on movement of the eyes. Associated with this is an intense headache which also worsens when the eyes are moved.
The excessive pressure on the eyeball can also lead to blurred vision.
The bulging of the eyeballs is called proptosis. Proptosis can be cosmetically unpleasant and makes patients very wary of how their eyes look.
Proptosis leads to what is called a ‘staring’ look. This is where the pupils and iris are clearly seen, along with a large portion of the ‘white’ of the eyeball. Some people compare it to a ‘startled’ look.
Strabismus is the medical term for squint. Due to the pushing of the eyeballs out of the socket, the position of the eyeball may not be symmetrical to each other.
In other words, the eyes may not bulge out in a straight manner. Furthermore, the excessive tissue behind the eyeball makes eye movements harder and more restricted.
This restricted movement can lead to a squint (strabismus) along with double vision.
The optic nerve is the nerve that is responsible for transmitting images that we see in the form of electrical signals to the brain. It is located at the back of the eye and is surrounded by fat tissue and muscle.
In advanced cases of Grave’s disease, the excessive fat and muscle tissue growth behind the eyeball can place a great deal of pressure on the optic nerve. This compression of the nerve can lead to a condition called optic neuropathy.
Optic neuropathy causes blurred vision, and in rare cases can lead to irreversible blindness.
Some other symptoms that patients with thyroid eye disease may experience include lid tremor (when eyes are closed), infrequent blinking, difficulty eversing the eyelid and decreased forehead wrinkling.
Thyroid eye disease can be diagnosed from clinical examination. A thyroid function test can confirm the presence of Grave’s disease.
A CT scan of the orbit may show inflamed and enlarged tissues behind the eye. An MRI scan may also be useful.
There are some simple measures that can be taken to help treat thyroid eye disease.
Applying a cool pack can soothe the eyes as the moisture can provide a degree of relief. Wearing protective sunglasses is important as excessive exposure of the cornea of the eye to sunlight can lead to problems with vision.
As dryness of eyes is a common problem, ophthalmologists often prescribe lubricating eye drops. These can keep the eyes moist and prevent the grittiness experienced when blinking.
Facial swelling is a common problem that can be avoided by elevating the head end of the bed when sleeping. Swelling can also be treated with the help of steroids eye drops.
Prescription glasses with prisms may help some people with double vision.
There are different surgical procedures that could help patients with thyroid eye disease.
As previously noted, lid lag is a common problem leaving a large part of the cornea exposed. Repositioning the eyelid can prevent over-exposure of the cornea, preventing ulcer formation.
Muscle infiltration that is seen in Grave’s ophthalmopathy can lead to scarring as time passes. Scarring makes the eye muscles shorter than normal, prohibiting smooth eye movements. As time passes, this can lead to double vision. Surgical resection of these muscles and reattachment to allow better movement and easy reading is often done to treat this problem.
In advanced cases of eye disease when eyesight itself is threatened, orbital decompression surgery is necessary. Here, the eye socket bone (orbit) is removed so as to allow extra space from the sinuses for eye movements. As time passes, the vision improves as there is more room for the swollen tissues to sit and for the eye to move. However, this surgery does bear certain risks of double vision in rare cases.
Always ensure that all surgical procedures are performed after the risks and benefits have been explained by expert ophthalmologists.
Once thyroid eye disease has been treated, it is important to keep the thyroid function within normal limits. This can be achieved through medical therapy. The long term prognosis is generally good.
There are no specific preventive measures to avoid thyroid eye disease. However, when treatments are ongoing for Grave’s disease, steps may be taken to prevent eye disease from getting any worse.
For example, if radio-iodine therapy is being prescribed, there is always a chance that eye disease could worsen. Co-prescribing steroids could help prevent this.
Stopping smoking can prevent worsening of eye disease.