Introduction

Excessive thyroid hormone circulating in the blood leads to a condition called ‘hyperthyroidism’. ‘Thyrotoxicosis’, though often used interchangeably with ‘hyperthyroidism’, is the clinical manifestation at the tissue level due to abnormally high levels of circulating thyroid hormone (T3 and T4) in the body. Excessive thyroid hormone levels in the blood affect different parts of the body differently. When this excessive thyroid hormone in the blood leads to swelling and inflammation of the tissues around the eyes, it is called ‘Ophthalmopathy’.

Understanding thyrotoxicosis

Thyroid hormone is crucial for regulating various bodily functions including metabolism (process of converting food into energy), heart rate, body temperature, digestive functions, and overall body development and maintenance. An overactive thyroid gland (hyperthyroidism), is the most common cause of thyrotoxicosis.

Definition of thyrotoxicosis

The medical condition is characterised by an excess of thyroid hormone in the bloodstream, regardless of the underlying cause. The clinical presentation of thyrotoxicosis ranges from asymptomatic to severe life-threatening complications, such as thyroid storm/thyoid crisis.

Causes

• Hyperthyroidism or Graves’ disease
• Toxic multinodular goitre
• Thyroiditis
• Toxic adenoma
• Pituitary adenoma
• Drug-induced thyrotoxicosis

Signs and symptoms 

Signs and symptoms associated with thyrotoxicosis include:

• Increased sweating
• Increased sensitivity to heat
• Intolerance to heat
• Increased heart rate (tachycardia)
• Irregular heartbeat (arrhythmia)
• Palpitations
• Explained weight loss
• Increased weight loss
• Increased bowel movements
• Tremors or shakiness of the hands
• Moist palms
• Muscle weakness
• Fatigue
• Nervousness or anxiousness
• Amenorrhea (absence of periods) or oligomenorrhea (infrequent periods)
• Hair loss

Diagnosis

Thyrotoxicosis is diagnosed using a combination of physical or clinical examination, a group of blood tests called the thyroid function tests and imaging techniques such as an ultrasound or radioactive iodine uptake scan.

What is ophthalmopathy?

Definition

Ophthalmopathy is an autoimmune inflammatory condition that affects the eyes and tissues around the eyes, causing swelling, bulging of the eyes and vision impairments.²

Other names

Graves’ ophthalmopathy, or Thyroid Eye Disease (TED) or Thyroid-associated orbitopathy, or Thyroid-associated ophthalmopathy.

Symptoms

• Swelling of the eyelids
• Swelling and redness of the conjunctiva
• Proptosis or bulging eyes (due to increased intraocular pressure)
• Dryness and irritation of the eyes
• Feeling of pressure behind the eyeballs
• Double vision (diplopia) 
• Restricted movement of the eye
• Sensitivity to light

Link between thyrotoxicosis and ophthalmopathy

Thyrotoxicosis affects the eyes and their surrounding tissues, leading to disorders affecting the eyes. Thyroid-associated ophthalmopathy is an autoimmune condition in which the body’s own immune system attacks the eyes and their surrounding tissues, leading to inflammation and swelling.

Diagnosis of ophthalmopathy associated with thyrotoxicosis

Diagnostic techniques

Clinical presentation: 

• Exophthalmos: One of the classic signs of ophthalmopathy is exophthalmos (proptosis) or bulging of the eyeball. This happens due to increased intraocular pressure and deposition of fat behind the eyeball
• Eyelid retraction: Due to muscle weakness and dysfunction, the upper eyelid is elevated or retracted
• Periorbital oedema: Due to inflammation, there is swelling around the eyes
• Impaired vision: As the muscles of the eye become weak and dysfunctional, there is impaired eye movement leading to changes in the vision, such as double vision, blurring or restricted movement of the eye
• Irritation or dryness of the eyes
• Photophobia: Increased sensitivity to light and increased tearing of the eyes

Physical examination:

• Inspection of the eyelids and the conjunctiva: Eyelid retraction and chemosis (swelling of the conjunctiva) may be observed.
• Palpation of the orbits: Increased orbital volume due to swelling of muscles and fat in the eye socket.
• Assessing ocular motility: Restrictions in eye movement suggest muscle involvement.

Blood tests:

• Thyroid function tests (TFTs): Blood tests, such as thyroid function tests and thyroid antibodies, are measured to diagnose thyrotoxicosis
  • In Graves' disease, there is typically a low TSH level with elevated free T4 and free T3 levels
  • The presence of TSH receptor antibodies can confirm Graves' disease

Ultrasound: This may be used to assess the size of the optic nerve and muscle enlargement

Orbital imaging (CT or MRI scans): These are used to assess the extent of the disease, especially in moderate to severe cases.

• CT Scan: show any changes in the eye socket
• MRI: shows any muscular changes, swelling, fat deposition and compression of the optic nerve if present

Visual acuity and fundoscopy: They are used to assess changes in vision due to impairment or involvement of the optic nerve

Classification and severity sssessment¹

The NOSPECS classification system is used to assess the severity of thyroid eye disease:

• N: No signs or symptoms
• O: Only signs, no symptoms
• S: Soft tissue involvement (lid retraction, swelling, etc.)
• P: Proptosis (exophthalmos)
• E: Extraocular muscle involvement (restricting eye movement)
• C: Corneal involvement (keratopathy, dryness, etc.)
• S: Severe optic neuropathy

The Clinical Activity Score (CAS): This score is used to assess the disease based on symptoms such as pain, swelling, and redness.

Differential diagnosis

• Orbital Cellulitis: Inflammation and infection of the orbital tissues, often accompanied by fever and severe pain
• Tumours or Mass Lesions: Any masses in the orbit can present with proptosis or similar symptoms
• Orbital Pseudotumor: This is an idiopathic inflammatory condition that can cause orbital pain and proptosis
• Other causes of thyroid disease: Hypothyroidism and Hashimoto’s thyroiditis, though less common, can occasionally lead to orbital changes

Treatment and management of ophthalmopathy 

Treatment of ophthalmopathy depends on the severity of the disease and may range from the use of medication such as steroids, thyroid hormone regulation, radioactive iodine therapy, and immune-modulating therapies to surgical interventions that may include orbital decompression or strabismus (misalignment of the eyes) surgery in severe cases. Referral to an ophthalmologist or an endocrinologist is usually required for a comprehensive management approach.³

Prognosis and long-term consideration

Prognosis of the condition depends on its phase- active, inactive or recurrent – and the severity of the condition – mild, moderate or severe.¹ Usually, early diagnosis and ongoing care are key to preventing serious complications. Regular eye checkups, thyroid level monitoring can help manage the condition and maintain a good quality of life. In severe cases, surgery followed by ongoing care may be required to prevent permanent damage to the eyes and vision. 

FAQs

What is the thyroid disease that affects the eyes?

The thyroid disease that affects the eyes is known as Grave’s ophthalmology or thyroid eye disease (TED).

What is Grave’s ophthalmopathy?

Grave’s Ophthalmopathy or thyroid eye disease (TED) is an autoimmune condition that affects the eye and its surrounding tissues with symptoms such as bulging eye, irritation and redness of the eyes, swelling around the eyes and retraction of the upper eyelid.

How to remember eye signs of thyrotoxicosis?

Eye signs of thyrotoxicosis can be remembered by using the mnemonic- NOSPECS

• N: No signs or symptoms
• O: Only ocular irritation (dryness, gritty sensation)
• S: Soft tissue involvement (conjunctival oedema or injection)
• P: Proptosis
• E: Extraocular muscle involvement
• C: Corneal exposure and ulceration
• S: Severe optic neuropathy

Summary

Ophthalmopathy, or thyroid eye disease (TED), is a common complication of thyrotoxicosis, particularly in patients with Graves' disease. It is characterised by inflammation and swelling of the tissues around the eyes, including the extraocular muscles, orbital fat, and connective tissue. This can lead to a range of symptoms, including eye dryness, bulging eyes (exophthalmos), double vision (diplopia), eye pain, and in severe cases, loss of vision.

The primary cause of thyroid eye disease is an autoimmune response, where the body’s immune system attacks the tissues around the eyes. This results in inflammation and fluid accumulation, which can cause the eyes to protrude. While the exact cause is unclear, the condition is often linked to hyperthyroidism, particularly in patients with uncontrolled thyroid hormone levels.

Long-term complications of thyroid ophthalmopathy can include compressive optic neuropathy, which occurs when the swollen tissues put pressure on the optic nerve, potentially leading to permanent vision loss. Patients may also experience chronic dry eyes, corneal damage, and strabismus (misalignment of the eyes).

Treatment focuses on controlling thyroid function through medications, radioactive iodine therapy, or surgery. Steroids may be used to reduce inflammation, and in severe cases, surgical options like orbital decompression or corrective surgery for double vision may be necessary. Regular monitoring of thyroid levels and eye health is crucial for preventing long-term complications and improving patient outcomes.