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), aqueous humour can no longer escape, and 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 is a sudden, severely painful, red eye with blurred vision and haloes around lights, accompanied by headache, nausea and vomiting. The eye often feels hard to the touch.
The key skill in primary care is twofold: 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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