GPAtlas🧭 When to suspect
Acute angle-closure glaucoma (AACG) is a sight-threatening ophthalmic emergency.
• The peripheral iris suddenly blocks the eye's drainage angle (the trabecular meshwork), so aqueous humour can no longer escape.
• The intraocular pressure (IOP) rises steeply within hours.
• The pressure spike causes intense pain and, if not relieved quickly, ischaemic damage to the optic nerve and irreversible visual loss.
The usual trigger is pupil mid-dilation – from dim light (an evening, a darkened cinema) or a mydriatic drug – which brings the iris forward against the lens and seals off aqueous flow (“pupillary block”).
The classic picture:
• A sudden, severely painful, red eye with blurred vision and haloes around lights.
• Accompanying headache, nausea and vomiting.
• The eye often feels hard to the touch.
Recognise the pattern among the many causes of a red eye, and refer the same day – never wait for investigations.
| Condition | Typical pupil | Discriminating features |
|---|---|---|
| Acute angle-closure glaucoma | Mid-dilated, fixed, vertically oval | • Severe pain, haloes, hazy (“steamy”) cornea, hard globe, reduced acuity, nausea/vomiting • IOP very high |
| Anterior uveitis (iritis) | Small, sometimes irregular | • Deep ache, marked photophobia, watering, circumcorneal redness • Vision mildly reduced • IOP usually normal |
| Acute conjunctivitis | Normal, reactive | • Gritty rather than painful, discharge, diffuse redness • Vision normal, no haloes |
| Scleritis | Normal | • Boring deep pain that can wake from sleep, bluish/violaceous hue, tender globe • Vision usually preserved • Often systemic disease |
Raise suspicion particularly in older patients, in women (more commonly affected), in those of East or South-East Asian or Inuit heritage, in long-sighted (hypermetropic) eyes, and where there is a family history of angle closure. AACG is rare in short-sighted (myopic) eyes.
Source: Royal College of Ophthalmologists · College of Optometrists
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