Thyroid ophthalmopathy: what is it?
Thyroid ophthalmopathy – also known by the medical term Basedownian ophthalmopathy – is one of the clinical manifestations of Basedow-Graves Disease, i.e. an autoimmune thyroid disease, easily recognisable by its distinctive sign or symptom: the abnormal protrusion – called exophthalmos or proptosis – of the eyeballs outwards
In the context of an autoimmune thyroid disease, where the immune system is activated against the thyroid gland, certain cells or tissues – the eyes, in this case – are also misrecognised by the immune system as targets to fight, and consequently attacked.
This ocular pathological condition related to thyroid autoimmunity can be further aggravated by certain therapies aimed at treating the thyroid itself, such as surgical removal of the thyroid gland (thyroidectomy), causing the eyeballs to protrude further and creating injuries or compressions to extraocular muscles and the optic nerve.
The latter, if predominantly affected, may impede the proper exchange of information in the form of electrical impulses between the eye and brain, resulting in impaired vision.
Thyroid ophthalmopathy occurs more frequently in females than in males.
What are the causes and risk factors of thyroid ophthalmopathy?
Thyroid ophthalmopathy is an autoimmune-based disease and the risk factors involved in its occurrence are essentially genetic predisposition, female gender, age, thyroid dysfunction and – according to recent analyses – it appears that smokers are at greater risk of developing this disease.
T lymphocytes – immune cells that normally come into action in order to defend the organism from external attack by viruses or aggressive bacteria – also come into action in the absence of real danger, mistakenly going to attack healthy tissues believing them to be foreign and potentially dangerous.
Tissues that, in this case, are precisely the ocular and periocular ones.
This attack by the T lymphocytes triggers the start of an inflammatory process that consequently causes the eye muscles and tissues to increase significantly in volume, causing the bulbs to leave their physiological seat, protruding outwards.
Thyroid ophthalmopathy: recognising the symptoms
The manifestations by which thyroid ophthalmopathy is characterised are many and often very different; this wide range of symptoms varies depending on the severity with which the disease itself presents itself.
It is characterised by:
- Exophthalmos: i.e. protrusion, the protrusion of the eyeball outside its physiological seat. It is to all intents and purposes the first characteristic symptom of ophthalmopathy, as well as of this autoimmune form of hyperthyroidism. Exophthalmos is caused – as already mentioned – by increased volume of ocular tissues. It usually presents as bilateral, although the degree of protrusion often differs between the two eyes.
- Fixed gaze, with a ‘frightened expression’.
- Eye pain, especially during eye movement.
- Eyelid retraction resulting in incomplete eyelid closure. This characteristic is likely to make the proptosis of the bulb appear much more pronounced than in reality.
- Tremor of the eyelid when squinting.
- Reduction in both the frequency and amplitude of eyelid closure.
- Eyelid oedema.
- Dry eye, foreign body sensation, excessive tearing.
- Chemosis: an accumulation of fluid in the conjunctiva.
- Conjunctival hyperemia, i.e. reddening of the eye due to dilation of the blood vessels running through it.
- Corneal alterations, such as keratitis or ulcers, which occur when the eyelid can no longer adequately protect the cornea, resulting in the creation of lesions or real holes in the cornea.
- Photophobia: increased sensitivity to light.
- Blurred vision.
- Increased intraocular pressure.
- Optic neuropathy as, in cases of elevated exophthalmos, there may be signs of optic nerve compression distress.
Diagnosing thyroid ophthalmopathy
When thyroid ophthalmopathy is suspected, it is clear that the pathology affects two very different areas of medicine: ophthalmology and endocrinology.
Precisely for this reason, in order to reach a certain diagnosis, the investigation work must be carried out as a team, with a team that sees the symbiotic work of an ophthalmologist specialist and the endocrinologist.
During the specialist visit, the two specialists – after taking an accurate anamnesis, so as to highlight any other pathologies or the patient’s lifestyle habits – will immediately proceed with prescribing some specialist tests useful for investigating on both fronts the real nature of the symptoms complained of by the patient.
Thyroid dysfunction will have to be treated upstream by the endocrinologist, so as to eliminate the primary cause that generates thyroid ophthalmopathy at its base.
Subsequently, the ophthalmologist prescribes certain diagnostic tests, including visual acuity examination, ocular motility assessment, exophthalmometry, slit-lamp examination, tonometry, ophthalmoscopy and CT scan.
The eye test or visual acuity test will be useful to investigate visual acuity and colour perception.
Exophthalmometry is a diagnostic test to measure the protrusion of the eyeball in relation to the outer edge of the orbit.
To perform the test, an instrument known as a Hertel exophthalmometer is used.
Ophthalmoscopy, on the other hand, is a specialist test that uses an instrument – the ophthalmoscope – that is able to project a beam of light onto the retina through the pupil and, thanks to this, the ophthalmologist is able to draw information about the internal structures of the patient’s eye, especially if these structures are altered, torn or damaged.
A CT scan, on the other hand, may be useful for assessing the contents of the orbit.
Thyroid ophthalmopathy: the most appropriate therapy and possible complications
Once the team led jointly by the ophthalmologist and endocrinologist has arrived at a diagnosis consistent with the symptoms reported by the patient and the results of the tests conducted, a specific treatment can be jointly devised to put an end to the condition of thyroid ophthalmopathy.
In forms in which the thyroid ophthalmopathy is only mild, drug therapy based on the use of eye drops with artificial tears, which reduce dryness of the eye, may be sufficient.
The use of beta-blocking eye drops or corticosteroids is indicated in cases of both increased eye tone and general inflammation in the affected area.
In forms of thyroid ophthalmopathy that are particularly severe and accentuated, surgical therapy will be necessary, which consists of an operation to decompress the orbital cavity.
During the operation, an attempt is made to remove the bony wall between the orbit and the paranasal sinuses, so that the inflamed fat can be drained first and then the orbital space can be significantly increased, so that the eyeball can fit back into the orbit, its physiological seat.
Decompression surgery is an operation that unfortunately has many risks and complications.
The most common – though not frequent – are an inadequate result, the possible leakage of cerebrospinal fluid, sinus disorders and misalignment of the eyeballs resulting in diplopia.