Proptosis (bulging eyes): UK causes and when to worry

Proptosis — sometimes called exophthalmos — means one or both eyes protrude further forward than normal. It is always a sign that something behind the eye is pushing it out, and the underlying cause matters more than the appearance itself. Most cases in UK adults are due to thyroid eye disease, but imaging is important to exclude other causes.

How proptosis is measured

Proptosis is measured with a Hertel exophthalmometer. Normal ranges are roughly 12–22mm depending on ethnicity. A difference of more than 2mm between the two sides is significant regardless of the absolute number.

Common causes

**Thyroid eye disease (Graves' orbitopathy)** — the commonest cause in UK adults. Usually both eyes but often asymmetric. Associated with lid retraction, staring appearance, dry eye and double vision.

**Orbital tumours** — benign lesions such as cavernous haemangiomas, lymphomas, or metastases. Usually unilateral and slowly progressive.

**Orbital inflammation** — idiopathic orbital inflammatory disease (pseudotumour), IgG4-related disease.

**Orbital cellulitis** — acute proptosis with severe pain, redness and fever. A medical emergency.

**Vascular malformations** — carotid-cavernous fistula produces pulsatile proptosis with a bruit.

**High myopia** — very short-sighted eyes are longer front-to-back and can look mildly proptotic without disease.

Red-flag symptoms — same-day review

- Sudden proptosis over hours to days

- Severe pain, redness, fever (possible orbital cellulitis)

- Loss of vision, colour desaturation, or an afferent pupillary defect (optic nerve compression)

- Complete inability to move the eye

Any of these means the same-day emergency eye service or A&E.

Investigation

A first assessment includes:

- Full eye examination with visual fields and colour vision

- Hertel measurement

- Thyroid function tests, TSH receptor antibodies

- CT or MRI of the orbits

- Ophthalmic specialist review, and often an endocrinology or oculoplastic opinion

Treatment

Treatment depends on cause. Thyroid eye disease is managed with selenium supplementation and lubricants in mild cases, and steroids, teprotumumab, orbital radiotherapy or decompression surgery in more severe cases. Orbital tumours are managed by biopsy or excision. Cellulitis needs intravenous antibiotics.

Book a consultant-led orbital assessment

If you are worried about a change in the appearance of your eyes, or a difference between the two sides, book a consultation with my private practice or call **020 3137 3237**. Same-week specialist assessment and imaging can be arranged.