Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 7 Sept 2026Clinical review pending
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A new third-nerve palsy needs urgent imaging
A compressive aneurysm can cause a third-nerve palsy even when the pupil remains reactive. Severe headache, neurological deficits or reduced consciousness increase the urgency.
Action: Arrange immediate emergency assessment for suspected aneurysm or stroke. Every acute isolated third-nerve palsy requires prompt specialist assessment and neurovascular imaging; do not use pupil sparing to justify observation.
Synopsis
Recognise ocular motor nerve patterns, identify emergencies behind binocular diplopia, and arrange appropriate investigation and recovery support.
Binocular diplopia disappears when either eye is covered; persistent doubling in the uncovered eye suggests an optical or ocular cause.
Third-nerve palsy may combine ptosis with impaired adduction, elevation and depression; pupil findings do not reliably exclude aneurysm.
Fourth-nerve dysfunction usually produces vertical or tilted images, often troublesome when reading or descending stairs.
Key red flags
A new ocular motor palsy with severe headache, pupil enlargement or other neurological signs needs emergency hospital assessment.
Investigation priorities
01
Urgent neurovascular imaging for an acute third-nerve palsyFirst step
Exclude an aneurysm or other compressive lesion before assigning a microvascular explanation.
Management branches
EmergencyNew third-nerve or complex palsy
Acute third-nerve dysfunction or diplopia with neurological, orbital or severe headache red flags.
Arrange immediate hospital assessment when aneurysm, stroke, infection or another dangerous intracranial process is suspected.
Document onset, pupils, acuity, eye movements and neurological findings without delaying emergency referral for a complete clinic work-up.
AssessmentSelected isolated fourth or sixth palsy
A stable isolated deficit has been assessed and no emergency feature has been found.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 7 Sept 2026; clinical approval remains outstanding.