Diplopia, also known as double vision, happens when there is a mismatch in images produced by the two eyes; hence there is misalignment in the images produced. Diplopia can be subdivided into monocular and binocular, and horizontal and vertical. Binocular diplopia (89%) is far more common than monocular diplopia. Aetiology can be attributed to ophthalmological or neurological.  

Common causes

The table below highlights some of the common causes of diplopia.

Corneal pathologiesStrabismus
CataractsIsolated cranial nerve palsy
Macular degenerationRestrictive aetiology
Post ocular surgeryMyopathies
Multiple sclerosis
Common causes of monocular and binocular diplopia

History taking

During history taking, the following characteristics of diplopia need to be determined:

  • Monocular or binocular
    • Monocular: diplopia usually continues even when the other eye is covered, or when the patient looks in the other direction
    • Binocular: diplopia disappears if either eye is covered
  • Horizontal, vertical or oblique
  • Persistent or intermittent
  • Worse at near vision or far vision

When patients suffer from diplopia, the following associated clinical features may also be present:

  • Headache
  • Ptosis
  • Nausea and vomiting
  • Glare
  • Abnormal eye movement
  • Hemiparesis
  • Cerebellar sign

Refer to the Eye History & Exam and How to Use an Ophthalmoscope articles for a more detailed guide on eye history taking and examination.

Monocular diplopia

Corneal pathologies
1. Refractive error
• Refractive errors such as myopia, hypermetropia, astigmatism
• Diplopia improves with pinhole or blinking

2. Keratoconus
• A degenerative condition that causes the cornea to thin progressively and bulges outwards to form a cone shape.
• This can be treated with glasses and contact lens; ultimately, patient may require keratoplasty

3. Dry eye syndrome
• Dry eye syndrome can occasionally cause diplopia due to uneven tear film
• The diplopia improves with blinking

4. Corneal scarring
• This is usually secondary to corneal trauma or infection and causes corneal haziness
• Topical steroids can be considered but should only be given under specialist supervision


• This causes the lens to become less transparent and as a result incoming light is scattered by the cloudiness of the lens
• Associated symptoms include: blurry vision, light sensitivity, seeing halos, reduction in colour sensitivity and poor night vision

Macular degeneration

• The diplopia in macular degeneration often presents with “bent” or “warped” images
• There is a reduction in visual acuity (particularly near vision), contrast sensitivity and visual field.
• Photopsia and light glare may also be present

Post-ocular surgery

• Diplopia can happen after surgical intervention, such as iridotomy, glaucoma surgery, refractive surgery and scleral buckling surgery
• The diplopia is usually constant
• Dislocated intraocular lens causes diplopia at the lens edge within the visual axis

Binocular diplopia

Strabismus (Squint)

  • Most strabismus is due to abnormal neuromuscular control of eye muscles
  • Stroke is the leading cause in adults. Other less common causes include Graves’ disease and trauma.
  • Overall, it causes diplopia in adults and amblyopia in children
  • Non-paralytic (concomitant) strabismus
    • Children usually present with compensatory head tilt to minimise diplopia
    • Adults often complain of diplopia, alongside a headache and ocular discomfort
  • Paralytic (incomitant) strabismus
    • Diplopia is maximal when the patient looks in the direction produced by the weak muscle
  • The patient should be referred to an ophthalmologist or neurologist for further investigation and treatment
Isolated cranial nerve palsy

1. CN III (oculomotor) palsy

  • The aetiology of CN III palsy is mainly divided into ischaemic (96%) and compressive (4%)
  • The ocular features include:
    • Ptosis – due to paralysis of muscles supporting the upper eyelid
    • “Down and out” gaze at rest – the unopposed activity of superior oblique and lateral rectus
    • Eye movement – unable to elevate, depress or adduct eye
    • Diplopia – not always present as ptosis acts as a barrier to diplopia
    • Pupil
      • Pupil sparing is due to an ischaemic aetiology (and rarely, cavernous sinus syndrome)
      • Fixed and dilated pupil with loss of accommodation is due to a compressive aetiology (could be an indication of posterior communicating artery aneurysm, tumour or pituitary apoplexy)
CN III palsy
CN III (Oculomotor) Palsy

Patients with non-pupil sparing presentation should be referred urgently for neuro-ophthalmic evaluation (urgent CT and CTA).

2. CN IV (Trochlear) palsy

  • CN IV palsy is commonly caused by microvascular damage secondary to diabetes mellitus, hypertension, trauma or demyelinating conditions
  • Ocular features:
    • Diplopia – usually vertical and exacerbated by inward and downward gaze
    • Compensatory head tilt – in the direction away from the lesion
    • Ipsilateral hypermetropia
  • Fourth cranial nerve palsy secondary to microvascular aetiology usually resolve spontaneously in 4-6 weeks
  • Traumatic or congenital aetiology requires an ophthalmology referral so that the patient can be considered for an eye patch, prism or surgical management

3. CN VI (Abducens) palsy

  • This is the most common ocular motor palsy in adults as the Abducens nerve (CN VI) has the longest intracranial course of all the cranial nerves
  • Common aetiologies include vasculopathy and trauma
  • Ocular features:
    • Sudden onset (vascular aetiology) vs progressive onset (compressive aetiology)
    • Diplopia – horizontal and uncrossed, greater at distance than at near
    • Eye movement – inability to abduct eye
CN VI palsy
CN VI (Abducens) palsy
  • Microvascular aetiology usually resolves within 3 to 6 months
  • If an underlying or systemic cause is suspected, treat them primarily
Restrictive aetiology
Graves’ disease

  • In Graves’ disease the infiltration of lymphocytes causes oedema of the orbital fat and extraocular muscles
  • Ocular features:
    • Diplopia with ptosis, lid retraction and lid lag
    • Incomitant strabismus caused by restricted eye movement (especially on elevation and abduction)
Graves disease
Exophthalmos as seen in Graves’ disease
Myasthenia Gravis

  • Myasthenia Gravis is a neuromuscular disease which causes skeletal weakness, including extra-ocular muscles
  • Diplopia is intermittent with diurnal variation, tends to be worse towards the end of the day, and improves with rest
  • Ptosis is also present
Myasthenia gravis
Ptosis seen in Myasthenia Gravis
Multiple sclerosis

  • Multiple sclerosis is an autoimmune demyelinating condition affecting the central nervous system
  • Demyelination causes unilateral or bilateral internuclear ophthalmoplegia (INO)
    • The affected eye fails to adduct when attempting to gaze contralaterally (relative to the affected eye)
    • The non-affected eye would demonstrate dissociated horizontal nystagmus on abduction
  • Ocular features
    • INO presentation (as above)
    • Saccade (exclusively in the horizontal plane)
    • Upbeat or pendular nystagmus in the primary position
    • Ophthalmalgia
    • Loss of colour vision (especially red desaturation)
    • Light near dissociation
  • Visual loss and ocular movement deficit are indications of disease severity


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Written by Dr Charlotte Ho (FY1)
Reviewed by Ms Devina Gogi (Ophthalmology consultant)
Edited by Mudassar Khan (Y3 Medical Student)

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