Core Revision
Revision aid, not clinical advice. This page is educational material written for exam preparation. It is not a substitute for the current guideline or for clinical judgement, and must not be relied on for the care of any individual. Always check up-to-date national guidance and verify independently before acting on anything here.
The Red Eye Reasoner
Most red eyes are harmless — a few threaten sight. Instead of looking causes up, you’ll walk the path a clinician walks — history first, then pain, vision, pupil — and the tool will remember what you find hard and bring it back until it sticks. Revision aid, not clinical advice — always check the current guideline before treating real patients.
Reason mode: read a case, check the history first, then walk pain, vision and pupil — watch the differential narrow as you go.
0 · Does the history alone make this an emergency? (a chemical splash; a grinding, hammering or high-velocity injury; a hot, swollen eyelid with fever; a shingles rash on the forehead or nose)
1 · Is there true pain (not just grittiness)?
2 · Is vision affected?
3 · Is the pupil or cornea abnormal? (small/irregular, fixed & mid-dilated, hazy, or fluorescein uptake)
Differential — narrowing as you answer
The one call that matters most: same-day ophthalmology or routine? Make the danger call first, then name it.
Score 0 / 0
The mental model · benign eyes keep all three green
No true pain · normal vision · normal pupil & cornea. Break any one and you’re looking at the sight-threatening five (and a chemical splash, high-velocity trauma, a hot swollen lid with fever or a V1 shingles rash is urgent even when all three are green):
Pain, vision, pupil — in that order
A gritty, painless red eye with normal vision and a normal pupil is almost always benign. The moment a stem gives you true pain, reduced acuity, photophobia or an abnormal pupil — or mentions contact lenses — the answer shifts to same-day ophthalmology. Those three checks catch most dangerous causes — but ask about mechanism first: a chemical splash, high-velocity injury, shingles on the nose or lid swelling with fever overrides them.
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This tool is free. If you are preparing for the MRCGP AKT, the full course puts the same reasoning into exam-style questions: a question bank with Core Lens and Deep Dive explanations, a Core Calendar revision plan built around your exam date, and Core Compass to show you which topics need you next.
Preparing for the MSRA instead?
Sources last checked October 2026.
Core Revision Ltd is an independent educational platform and is not affiliated with the RCGP.
Written by practising UK GPs for exam revision. Sources are cited on this page and corrections are logged. Education only — always confirm against current guidance. Core Revision is an independent revision resource.