• Binocular diplopia is usually sinister (monocular not so)
  • Beware: new headache or ocular pain, unilateral pupil dilation, neurological features or fatigability, ptosis, facial trauma, papilloedema
  • Advise all patients with diplopia to stop driving


  • Monocular—diplopia persists when one eye is covered
  • Monocular generally = eye abnormality (cornea/ant chamber/lens/post chamber/retina) or non-organic
  • Binocular—Diplopia disappears when one eye is covered
  • Vertical diplopia = abnormal elevation/depression of eye:
    • Trauma
    • Fourth nerve palsy
    • Squint, T4 eye disease
  • Horizontal diplopia = abnormal ab/adduction of eyes
    • 6th nerve palsy
    • MS
    • Squint
  • Intermittent or fatigue diplopia - myasthenia gravis (±ptosis)
  • Check worse direction / triggering movement
  • Trauma - blow out # with entrapment
  • Sudden onset - acute aetiology e.g. ischaemia/vascular
  • Headache/eye pain - ischaemia, arterirtis, infection, ↑ICP, aneurysm
  • May indicate ischaemia, inflam., infection, ↑ICP, or aneurysm
  • Jaw claudication, temporal tenderness, myalgia suggest temporal arteritis
  • Check Hx for coagulopathy risks
  • Lamotrigine, topiramate, gabapentin, fluroquinolones, and citalopram are associated with diplopia

Red flags

  • New headache
  • New ocular pain
  • Unilateral mydriasis
  • Associated neuro. features
  • Fatigability
  • Ptosis
  • Facial trauma (ANY) eye signs
  • Papilloedema


  • Eyelid - ptosis = 3rd N palsy or myaesthenia
  • Eyelid - retraction = T4 disease
  • Proptosis = orbital disease (cellulitis, tumour, AVM) or T4
  • Record visual acuity
  • New poor vision = neurological or orbital
  • Fundoscopy (papilloedema)
  • Cranial and peripheral nerve examination
  • Check for strabismus in all directions (see diagram)
3rd 4th and 6th nerve palsy clues


  • Unilateral mydriasis, headache and diplopia (3rd N) = aneurysm
  • Meiosis (±ptosis) = Horner's (cavernous sinus or neck pathology)


Painful 3rd N palsy with ipsilateral dilated pupil or 6th nerve palsy with papilloedema

  • Discuss with your senior re imaging or refer neurology

Suspected giant cell arteritis

  • Request ESR/CRP. Start PO steroid treatment and refer medical

Trauma associated diplopia

  • Refer maxillofacial or ophthalmology

Long-standing or spectacle related diplopia or painless monocular diplopia

  • Ophthalmology OPD via GP

New isolated fourth and sixth cranial nerve palsies

  • Assume stroke (admit medical)

Suspected T4 eye disease

  • Check TFTs (results to GP). Stop smoking. GP follow up

Advise patients with diplopia not to drive.

Content by Dr Íomhar O' Sullivan . Last review Dr ÍOS 18/08/23.