[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Ophthalmology](https://durgical.com/en/ophthalmology/) › [Approach by symptom](https://durgical.com/en/ophthalmology/areas/approach/) › Double vision: monocular or binocular

# Double vision: monocular or binocular

- Clinical approach

Cover one eye. If the double image goes, the eyes are misaligned (nerve, muscle or brain); if it stays, the problem is inside that eye.

Updated Nov 5, 2026

**See it in 3D:** [Oculomotor nerve (III)](https://durgical.com/en/anatomy/oculomotor-nerve/) · [Trochlear nerve (IV)](https://durgical.com/en/anatomy/trochlear-nerve/) · [Abducens nerve (VI)](https://durgical.com/en/anatomy/abducens-nerve/) · [Lateral rectus](https://durgical.com/en/anatomy/lateral-rectus-muscle/) · [Superior oblique](https://durgical.com/en/anatomy/superior-oblique-muscle/) · [Medial rectus](https://durgical.com/en/anatomy/medial-rectus-muscle/)

## Key points

- Cover one eye: diplopia that persists is monocular (an eye problem).
- Third nerve palsy + dilated pupil = aneurysm until proven otherwise.
- Vertical diplopia worse going downstairs = fourth nerve palsy.
- Fatigable ptosis and diplopia, normal pupils = myasthenia gravis.

## What it is

Diplopia is seeing two images of one object. Monocular diplopia persists when the other eye is covered and comes from the optics of one eye: refractive error, cataract, dry eye or corneal irregularity. Binocular diplopia disappears when either eye is covered and means the eyes are misaligned: a cranial nerve palsy (III, IV, VI), myasthenia gravis, thyroid eye disease, an orbital fracture, or a brainstem lesion such as internuclear ophthalmoplegia.

## Red flags

- A dilated pupil with ptosis and an eye that is down and out: compressive third nerve palsy (posterior communicating artery aneurysm).
- Headache, papilloedema or vomiting: raised intracranial pressure (sixth nerve palsy can be a false localising sign).
- More than one cranial nerve, or other neurological signs.
- Fluctuating diplopia and ptosis that worsen through the day: myasthenia gravis, which can affect breathing.
- Over 50 with headache or jaw claudication: giant cell arteritis.
- A child, or after facial trauma with restricted upgaze, nausea or a slow pulse.

## Step-by-step approach

- Cover each eye in turn: monocular or binocular diplopia.
- For monocular diplopia, check whether a pinhole removes it: refractive or optical cause.
- Ask whether images are side by side or one above the other, and in which direction of gaze they separate most.
- Look for ptosis, pupil size and proptosis.
- Test eye movements in the nine positions of gaze and do a cover test.
- Ask about fatigability, thyroid disease, trauma, vascular risk factors and other neurological symptoms.

## Causes of binocular diplopia

| Cause | Pattern | Key sign | Next step |
| --- | --- | --- | --- |
| [Third nerve palsy, pupil involved](https://durgical.com/en/conditions/oculomotor-nerve-palsy/) | Mixed, with ptosis | Eye down and out, dilated pupil | Emergency CT or MR angiography |
| [Third, fourth or sixth nerve palsy, microvascular](https://durgical.com/en/conditions/oculomotor-nerve-palsy/) | By the nerve; over 50 with diabetes or hypertension | Pupil spared | Risk-factor control; image if atypical or not recovering |
| Sixth nerve palsy | Horizontal, worse looking to the side of the lesion | Eye does not abduct | Look for papilloedema; image if present |
| Fourth nerve palsy | Vertical, worse looking down (stairs, reading) | Head tilted away from the affected side | Image if no trauma or vascular cause |
| [Myasthenia gravis](https://durgical.com/en/conditions/myasthenia-gravis/) | Variable, worse late in the day | Fatigable ptosis, pupils normal | Antibodies, chest imaging for thymoma |
| [Thyroid eye disease](https://durgical.com/en/conditions/thyroid-eye-disease/) | Vertical or horizontal, worse in the morning | Lid retraction, proptosis, restricted upgaze | Thyroid tests, ophthalmology |
| [Internuclear ophthalmoplegia](https://durgical.com/en/conditions/multiple-sclerosis/) | Horizontal | Adduction fails on side gaze, nystagmus of the other eye | MRI (multiple sclerosis or stroke) |

## Keys to the differential

- The pupillomotor fibres run on the outside of the third nerve: compression dilates the pupil, while microvascular ischaemia usually spares it.
- Fourth nerve palsy is the commonest cause of vertical diplopia after head trauma.
- Myasthenia gravis never affects the pupil and can mimic any nerve palsy.
- In a child with a facial blow, restricted upgaze with nausea and a slow pulse suggests a trapped inferior rectus muscle (trapdoor fracture).

## Next step / Initial management

- Monocular diplopia: routine optometry or ophthalmology (refraction, cataract, dry eye).
- Third nerve palsy with pupil involvement, pain or other signs: emergency CT or MR angiography for an aneurysm.
- Isolated pupil-sparing palsy in a person over 50 with vascular risk factors: control glucose and blood pressure and expect recovery within about three months; image if young, atypical or not recovering.
- Suspected myasthenia: acetylcholine receptor antibodies, chest CT for thymoma, neurology; urgent if swallowing or breathing are affected.
- Diplopia with papilloedema, headache or other neurological signs: urgent brain imaging.

## Test yourself

Think of the answer, then tap the question to see it.

## Diplopia persists when the other eye is covered. Where is the problem?

In the optics of the uncovered eye: refractive error, cataract, dry eye or an irregular cornea.

## Why is a third nerve palsy with a dilated pupil an emergency?

Because it suggests compression of the nerve, typically by a posterior communicating artery aneurysm that can rupture.

## Which clinical feature suggests myasthenia gravis as the cause of diplopia?

Variability and fatigue: diplopia and ptosis that worsen through the day, with normal pupils.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/ophthalmology/double-vision-monocular-or-binocular/)

## Elsewhere in DurgiPedia

- [The visual pathway, pupillary reflexes and eye movements](https://durgical.com/en/physiology/the-visual-pathway-pupillary-reflexes-and-eye-movements/)
- [Eye exam: visual acuity, visual fields and eye movements](https://durgical.com/en/clinical-exam/eye-exam-visual-acuity-visual-fields-and-eye-movements/)

## Connections

## See it in 3D 6

The structures of Durgical's 3D anatomy where it is found.

- [Oculomotor nerve (III)](https://durgical.com/en/anatomy/oculomotor-nerve/)
- [Trochlear nerve (IV)](https://durgical.com/en/anatomy/trochlear-nerve/)
- [Abducens nerve (VI)](https://durgical.com/en/anatomy/abducens-nerve/)
- [Lateral rectus](https://durgical.com/en/anatomy/lateral-rectus-muscle/)
- [Superior oblique](https://durgical.com/en/anatomy/superior-oblique-muscle/)
- [Medial rectus](https://durgical.com/en/anatomy/medial-rectus-muscle/)

## Related 5

- [Eye movements and the cover test](https://durgical.com/en/ophthalmology/eye-movements-and-the-cover-test/)
- [Extraocular muscles and the cardinal positions of gaze](https://durgical.com/en/ophthalmology/extraocular-muscles-and-the-cardinal-positions-of-gaze/)
- [Drooping eyelid (ptosis)](https://durgical.com/en/ophthalmology/drooping-eyelid/)
- [Anisocoria: which pupil is abnormal](https://durgical.com/en/ophthalmology/anisocoria-which-pupil-is-abnormal/)
- [Proptosis and periorbital swelling](https://durgical.com/en/ophthalmology/proptosis-and-periorbital-swelling/)

## Related conditions 7

- [Oculomotor (third) nerve palsy](https://durgical.com/en/conditions/oculomotor-nerve-palsy/)
- [Myasthenia gravis](https://durgical.com/en/conditions/myasthenia-gravis/)
- [Thyroid eye disease (Graves orbitopathy)](https://durgical.com/en/conditions/thyroid-eye-disease/)
- [Multiple sclerosis](https://durgical.com/en/conditions/multiple-sclerosis/)
- [Orbital floor (blowout) fracture](https://durgical.com/en/conditions/orbital-floor-fracture/)
- [Giant cell arteritis](https://durgical.com/en/conditions/giant-cell-arteritis/)
- [Raised intracranial pressure and brain herniation](https://durgical.com/en/conditions/raised-intracranial-pressure-and-brain-herniation/)

## In Pharmacology 1

- [Pyridostigmine](https://durgical.com/en/pharmacology/pyridostigmine/)

[← All of ophthalmology](https://durgical.com/en/ophthalmology/)

Educational content; not a clinical guideline and no substitute for assessment by a health professional. For sudden visual loss, severe eye pain, a chemical burn or an eye injury, go to an emergency department at once.

Sources: [Diplopia](https://www.ncbi.nlm.nih.gov/books/NBK441905/) (StatPearls Publishing (NCBI Bookshelf), 2024); [Neuroanatomy, Cranial Nerve 3 (Oculomotor)](https://www.ncbi.nlm.nih.gov/books/NBK537126/) (StatPearls Publishing (NCBI Bookshelf), 2023); [Abducens Nerve Palsy](https://www.ncbi.nlm.nih.gov/books/NBK482177/) (StatPearls Publishing (NCBI Bookshelf), 2023); [Myasthenia Gravis](https://www.ncbi.nlm.nih.gov/books/NBK559331/) (StatPearls Publishing (NCBI Bookshelf), 2023).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/ophthalmology/double-vision-monocular-or-binocular/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/ophthalmology/double-vision-monocular-or-binocular/