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Diplopia

Binocular + painful or pupil-involved = the ones that kill.

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Your objective: explain the approach, recognize important warning signs, then test your recall.

Abbreviations explained
ACS
Acute coronary syndrome
OMI
Occlusion myocardial infarction
ECG
Electrocardiogram
PE
Pulmonary embolism
POCUS
Point-of-care ultrasound
QTc
QT interval corrected for heart rate
LBBB
Left bundle branch block
RBBB
Right bundle branch block
hs-cTn
High-sensitivity cardiac troponin
CTA
Computed tomography angiography
ICU
Intensive care unit
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The jobBinocular + painful or pupil-involved = the ones that kill.

  1. Monocular (optical) vs binocular (alignment): covering either eye kills binocular diplopia.
  2. Painful pupil-involving CN III = CTA now (PCOM aneurysm).
  3. Age ≥50: ask about jaw claudication and treat GCA on suspicion.
  4. INO or crossed signs: MRI-DWI, not a reassurance CT.

First decide monocular (optical: refractive, cataract, functional) vs binocular (alignment: nerve, muscle, NMJ, internuclear).

Binocular diplopia that is painful, pupil-involving, or accompanied by other neuro signs is a neurologic emergency — think posterior communicating artery aneurysm (CN III), giant cell arteritis, myasthenia, and brainstem stroke. Cover-uncover and a careful pupil exam do more than a CT.

Posterior communicating artery aneurysm (CN III) Critical

Key: Painful pupil-involving third-nerve palsy (down-and-out, ptosis, blown pupil) — CTA/MRA now, neurosurgery. A complete pupil-sparing CN III in a vasculopath >50 y is more often microvascular, but pain or incomplete palsies still get imaged.

Brainstem stroke / INO (internuclear ophthalmoplegia) Critical

Key: Sudden diplopia with ataxia, dysarthria, or crossed findings — posterior-circulation pathway, MRI-DWI. INO (impaired adduction + contralateral nystagmus) is MLF until proven otherwise.

Giant cell arteritis Critical

Key: Age ≥50, new headache, jaw claudication, diplopia or amaurosis — start glucocorticoids immediately to protect the other eye; ESR/CRP can be normal.

Myasthenic crisis Critical

Key: Fatigable binocular diplopia and ptosis, worse late in the day; pupils spared. Watch NIF/VC; avoid triggering antibiotics.

Cavernous sinus thrombosis / orbital apex Critical

Key: Diplopia + proptosis, chemosis, fever or CN V1 pain — CT/MR venography, antibiotics if septic, anticoagulation if atraumatic.

Botulism Emergent

Key: Descending paralysis, poorly reactive pupils, GI prodrome — antitoxin; do not wait for culture.

Microvascular cranial neuropathy / decompensated phoria Common

Key: Isolated pupil-sparing CN III/IV/VI in a diabetic or hypertensive adult often resolves — still arrange close follow-up and image if incomplete, painful, or not isolated.

Tick what your patient has — the banner updates as you go.

Monocular (persists covering one eye) vs binocular (resolves covering either)

Pain, headache, scalp tenderness, jaw claudication

Fatigability through the day, ptosis, dysarthria, limb weakness

Vascular risks, atrial fibrillation, trauma, recent infection or canned food

Cover-uncover / alternate cover; ductions and versions in nine positions

Pupils

size, reactivity, RAPD; complete vs pupil-sparing CN III

Fatigable ptosis (sustained upgaze); ice-pack test if MG possible

Orbital signs

proptosis, chemosis, resistance to retropulsion

Full neuro

INO, ataxia, other cranial nerves, temporal arteries

Bedside

  • Visual acuity, pupils, cover testing; glucose
  • Ice-pack or rest test if MG is likely and the patient is stable

Labs

  • ESR/CRP if age ≥50 with diplopia or GCA features
  • AChR/MuSK later; they do not change the ED airway decision

Imaging

  • CTA/MRA for painful or pupil-involving CN III
  • MRI-DWI ± CTA for brainstem/INO features
  • CT/MR orbits and cavernous sinus if orbital or febrile
Medication safety reminder

Use this as a first-pass prompt; verify all medications, doses, concentrations, contraindications, weight, pregnancy status, and local protocols before administration.

Check indication, allergy, route, renal/hepatic risk, interactions, monitoring, and local formulary.

Discharge

  • Clear monocular optical cause, or isolated pupil-sparing microvascular CN palsy in a vasculopath after a careful exam, with ophthalmology/neuro follow-up within days and return precautions.

Admit

  • Incomplete or painful cranial neuropathies pending imaging, MG under NIF observation, treated GCA on steroids, orbital infection on IV antibiotics.

Stroke / neurosurgery / ICU

  • PCOM aneurysm, brainstem stroke, cavernous sinus thrombosis, myasthenic crisis, botulism.

Use objective reassessment and the local pathway.

Before the next decision · reassess and hand over

Use these learning prompts with the presentation’s pathway. They are not discharge criteria.

  1. Reassess: compare symptoms, observations and examination with the initial assessment and response to treatment.
  2. Warning signs for Diplopia:
    • Painful pupil-involving third-nerve palsy
    • Age ≥50 with diplopia plus headache or jaw claudication
    • Proptosis, chemosis, or fever with diplopia
    • Fatigable weakness or falling vital capacity
    • Crossed findings, ataxia, or INO
    • Poorly reactive pupils with descending weakness (botulism)
  3. Reconsider: check unresolved findings and alternative explanations, including the pitfalls below.
  4. Escalate: communicate deterioration, uncertainty or needs beyond the current setting.
  5. Plan the transition: identify outstanding results, responsibility for follow-up, patient understanding and specific return advice.
Review this presentation’s disposition pathway →Practice a handover →

Clinical Pearls

  • Binocular + cover test: if covering either eye kills the double vision, it is alignment.
  • Painful pupil-involving CN III = CTA now, not “follow up with neuro.”
  • Diplopia in the over-50s is GCA until you have asked about jaw claudication and started steroids when the story fits.
  • INO is a brainstem localizer — skip the reassurance CT.

Pitfalls

  • Calling a pupil-involving CN III “microvascular” without vascular imaging misses a PCOM aneurysm.
  • Monocular diplopia is almost never a brain-attack — check refraction, dry eye, and the lens.
  • GCA diplopia can be fleeting and the ESR can be normal — treat on suspicion.
  • Myasthenia pupils are spared; if the pupils are involved, look elsewhere.
  • CT is a poor posterior-fossa test — MRI-DWI when INO or crossed signs are present.
PRACTICE REFRESHER

Rapid recall

Test your first action and the dangerous diagnoses before revealing the answer.

01 · First move

Before you scroll, what needs to happen first?

02 · Immediate threats

Name at least two diagnoses that cannot wait.

PRIVATE TO THIS DEVICE

Your learning note

Capture a weak point, a teaching pearl, or a question to take to your next shift.

Review schedule starts when marked reviewed
HeadacheRed Eye & Eye EmergenciesWeakness & FatigueDizziness & Vertigo

Selected guidance · source check 2026-09-07. These 1 source links support selected teaching points, not a complete review of this topic. Check population, setting and local protocol before applying a recommendation.

  • Rosen’s Emergency Medicine, 10th ed. (2023) — diplopia
  • 2026 AHA/ASA stroke guidance; SAEM GRACE-3 (2023) acute dizziness guideline
  • ACR/EULAR GCA recommendations; AAO cranial neuropathy guidance
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