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Diplopia (Double Vision): Causes, Types, Urgent Signs and Treatment
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Diplopia (noun; everyday term: double vision): diplopia is seeing two images of a single object. The two images can sit side by side, one above the other, diagonally or tilted, and they can be constant or come and go. It is a symptom, not a disease in itself, and it has two main types: monocular (in one eye, caused by the eye itself) and binocular (only with both eyes open, caused by the eyes not lining up). Squint (strabismus) surgery by Prof. Dr. Ahmet Satıcı is one treatment for binocular diplopia that glasses cannot fix.
Diplopia (double vision): key facts
- What it is
- Seeing two images of one object
- Quick home check
- Cover one eye. If the double image disappears, it is binocular (both eyes). If it stays, it is monocular (one eye)
- Monocular causes
- Dry eyes, astigmatism, cataract, keratoconus; rarely a retinal problem
- Binocular causes
- Most often misaligned eyes (squint), caused by eye-muscle or nerve problems; adult causes include diabetes, thyroid eye disease, myasthenia gravis, stroke, brain tumour and head injury
- Emergency signs
- Sudden double vision, double vision with eye pain, with a severe headache and an enlarged pupil, or after a head injury
- Main treatments
- Treat the cause: glasses or lenses, eye drops, cataract surgery, patching, prism glasses, eye exercises, botulinum toxin, eye-muscle surgery
- Specialist
- Ophthalmologist; for squint-related double vision at Laser Istanbul Clinic, Prof. Dr. Ahmet Satıcı
What is diplopia? Double vision meaning
Diplopia means seeing two images when you look at one object. The NHS describes it as looking at one object and seeing two, in one eye or in both. It is not usually serious in itself, the NHS says, but it is important to get it checked even if it comes and goes, because it can point to an eye-muscle problem or to a condition elsewhere in the body.
The word comes from the Greek for "double" and "sight". People describe it in different ways: two clear, separate copies of a letter or a face; a faint "ghost" beside the real image; or two images shifted sideways, stacked vertically or tilted. Where the second image appears, and when, gives your doctor useful clues, so notice it and write it down.
Double vision is different from blurred vision. With blur, one image is out of focus. With diplopia, there are two images, which may each be fairly sharp. A good result on the letter chart (your visual acuity) therefore does not by itself rule diplopia out.
Monocular vs binocular diplopia: how to tell the difference
The first question any doctor asks is whether the double image is still there when you cover one eye. According to the American Association for Pediatric Ophthalmology and Strabismus (AAPOS), monocular diplopia stays when the other eye is closed, while binocular diplopia is present with both eyes open and disappears when either eye is closed. The NHS suggests the same simple check: cover one eye at a time and see whether the double image goes away.
| Monocular diplopia | Binocular diplopia | |
|---|---|---|
| Double image with one eye covered? | Yes, it stays in the affected eye | No, it disappears |
| Where the problem is | In the eye itself: the cornea, lens or, rarely, the retina | In the eye muscles, the nerves that move them, or the brain |
| Typical causes | Astigmatism, dry eye, cataract, keratoconus | Misaligned eyes (squint), eye-muscle or nerve problems, thyroid eye disease, myasthenia gravis, stroke |
| Usual first step | Eye examination and glasses check | Eye examination, often with a search for the underlying cause |
| How serious? | Usually a focusing or eye-surface problem | In adults, can be a sign of a more serious condition, so get it checked promptly |
What causes double vision in one eye (monocular diplopia)?
Double vision in one eye is usually caused by a problem in the eye itself that makes the retina receive two images. AAPOS lists refractive errors such as astigmatism, dry eyes and cataracts as the typical causes, and notes that retinal problems are a rare cause. The NHS gives the same list and adds keratoconus. In more detail:
- Dry eye. An uneven tear film can distort the image. Artificial tears and dry-eye treatment are the treatments AAPOS lists. See also Glossary: Dry eye syndrome.
- Astigmatism. The cornea or lens is not perfectly round, so light does not focus at a single point. Glasses or contact lenses are the usual correction.
- Cataract. A clouded lens can cause double vision in one eye; AAPOS lists cataract surgery as the treatment.
- Keratoconus. The cornea thins and bulges into a cone shape. The NHS lists it among the causes of double vision in one eye.
Because monocular diplopia comes from the eye's own optics, it is often treatable once the cause is found. An irritated, allergic eye surface (see Glossary: Eye allergy) is worth mentioning to your doctor too if you notice both symptoms together.
What causes double vision in both eyes (binocular diplopia)?
Double vision that disappears when either eye is covered is caused by the two eyes pointing in slightly different directions. The NHS says binocular double vision is usually a symptom of a squint: problems with the eye muscles, or with the nerves that control them, make the eyes look in different directions. AAPOS says misalignment of the eye muscles (strabismus) is the most common cause of binocular diplopia.
Why children with a squint rarely see double
AAPOS explains that children who develop strabismus early often do not notice double vision because the brain learns to suppress the image from the turned eye. The American Academy of Ophthalmology (AAO) describes the other side of this: when a squint appears later in life, the brain cannot ignore the image from the turned eye, so the person sees two images. A squint that starts suddenly in adulthood, AAPOS says, almost always causes double vision.
Conditions that can cause adult-onset double vision
| Cause | What to know |
|---|---|
| Diabetes | Listed by the AAO among the health conditions behind adult squint |
| Thyroid eye disease (Graves' eye disease) | Listed by the AAO |
| Myasthenia gravis | The NHS lists double vision and drooping eyelids as main symptoms, typically worse when you are tired and often worse towards evening |
| Stroke or transient ischaemic attack (TIA) | Listed by the AAO and MedlinePlus; MedlinePlus advises emergency care for double vision, even if temporary |
| Brain tumour | Listed by both the AAO and MedlinePlus |
| Head injury | Listed by the AAO; the NHS treats double vision after a head injury as a 999 emergency |
| Earlier eye surgery | The AAO lists complications affecting the eye muscles |
| Giant cell (temporal) arteritis | The NHS lists double vision or loss of vision in one or both eyes as a symptom and says it needs urgent care, because untreated it can lead to stroke and blindness |
Most people with double vision do not have a life-threatening cause. But because some causes are serious, new double vision in an adult should always be assessed.
What are the symptoms of diplopia?
The main symptom is the double image itself. Features worth noticing and telling your doctor:
| What you notice | Why it matters |
|---|---|
| Image doubled side by side, above and below, diagonal or tilted | AAPOS notes the images can be horizontal, vertical, diagonal or tilted; the pattern helps your doctor find the cause |
| Constant, or comes and goes | AAPOS describes both patterns; intermittent double vision still needs checking (NHS) |
| Disappears when one eye is covered | Points to binocular diplopia (eye alignment) |
| Stays in one eye | Points to monocular diplopia (cornea, lens, tear film) |
| Worse when tired or later in the day | A typical pattern in myasthenia gravis (NHS) |
| Drooping eyelid | Listed with double vision in myasthenia gravis (NHS) |
| Eye pain, severe headache, an enlarged pupil, weakness, face drooping or slurred speech | Warning signs: see the next section |
Is double vision an emergency? Urgent signs
Sudden double vision is not something to wait out. This table follows NHS guidance:
| Situation | What to do |
|---|---|
| Double vision with a severe headache and a dilated (enlarged) pupil | Call emergency services (999 in the UK, 911 in the US and Canada, 112 in the EU and Türkiye) |
| Double vision after a head injury | Call emergency services |
| Double vision with face drooping, arm weakness or slurred speech | Call emergency services at once: these are stroke signs (NHS "FAST") |
| Sudden-onset double vision | Same-day medical help: an urgent GP appointment or NHS 111 in the UK, or an eye emergency service |
| Double vision with eye pain | Same-day medical help |
| Double vision with loss of vision in one or both eyes | Urgent care the same day; the NHS says temporal arteritis, which can cause this, can lead to stroke and blindness if not treated quickly |
| Double vision that comes and goes, or has been present for some time | Book an eye examination soon: the NHS says even double vision that comes and goes should be checked |
If your double vision started suddenly, deal with it where you live first. Any plan to travel for treatment can wait until the cause is known.
How is diplopia diagnosed?
Diagnosis starts with your story and simple, painless tests. The NHS says an optician or GP performs simple, painless eye tests and may refer you to a hospital eye specialist. An ophthalmologist usually:
Asks about the double vision
Is it in one eye or both? Horizontal, vertical or tilted? Constant or intermittent? When did it start, and have you had a head injury, diabetes, thyroid problems or other illness?
Checks the eyes
MedlinePlus lists a dilated eye exam, a slit-lamp examination, a refraction (glasses check) and an eye-pressure test among the tests used for vision problems.
Assesses how well the eyes line up and move
This is the key step in binocular diplopia, because it shows whether a muscle or a nerve is involved.
Looks for an underlying cause when needed
For some conditions, such as myasthenia gravis, the NHS says doctors may order blood tests, nerve function tests or scans.
When you send us your eye report, include the date the double vision began, whether it is in one eye or both, and any scans you already have.
How is double vision treated?
Treatment depends on the cause, and the aim is to remove the double image, or at least reduce it. AAPOS notes that treatment may reduce rather than completely eliminate double vision. The NHS lists eye exercises, an eye patch, and glasses or contact lenses as options, with surgery for some conditions.
| Treatment | What it does | Typically used for |
|---|---|---|
| Glasses or contact lenses | Correct refractive errors such as astigmatism | Monocular diplopia from astigmatism; some binocular cases |
| Artificial tears and dry-eye treatment | Restore a smooth tear film | Monocular diplopia from dry eye |
| Cataract surgery | Replaces the clouded lens | Monocular diplopia from cataract (AAPOS) |
| Blurring or covering one eye (patching) | Removes one of the two images | Binocular diplopia (AAPOS, NHS) |
| Prism glasses | Bend light so the two images line up; the AAO says they correct mild double vision | Small misalignments in binocular diplopia |
| Eye exercises | Improve eye coordination; the AAO lists exercises for convergence insufficiency | Convergence insufficiency |
| Botulinum toxin injection | Temporarily weakens one eye muscle to improve alignment; the NHS says the effect lasts under 3 months | Selected binocular cases |
| Strabismus (eye-muscle) surgery | Loosens, tightens or repositions eye muscles to straighten the eyes | Persistent binocular diplopia from a squint that other treatments cannot correct |
| Treating the underlying disease | For example the thyroid, diabetes or myasthenia treatment your doctor prescribes | Diplopia caused by a general condition |
Can surgery fix double vision?
Often, yes: surgery can straighten the eyes and reduce binocular double vision, but results vary. The AAO says surgery is the main intervention for adult strabismus and that it is never too late to treat it. AAPOS says most people see a big improvement in eye alignment after one operation, although more than one is occasionally needed, and that it can also improve depth perception (see Glossary: Stereopsis).
How the operation works: the surgeon either weakens a muscle by moving it back (recession) or strengthens it by shortening or folding it (resection or plication). In adults the muscle can be held with adjustable stitches that are fine-tuned after the operation, with the eye numbed and the patient awake (AAPOS).
Surgery has risks, and double vision itself can be one. EyeWiki reports temporary double vision after surgery in 9% of adults, usually settling within 6 weeks, and persistent, troublesome double vision in 0.8%. It also says around 20% of adults do not reach satisfactory alignment with one procedure. Your surgeon should go through these figures with you and say whether your cause is suitable for surgery.
Treatment with us: squint surgery for adults and children, including for double vision, is performed by Prof. Dr. Ahmet Satıcı in a fully equipped, Ministry of Health–licensed operating theatre in Istanbul. He first examines the eyes and recommends an operation only when glasses, prisms or other treatment are not enough.
When to see a doctor about double vision
See a doctor the same day for:
- double vision that started suddenly
- double vision with eye pain, a severe headache or an enlarged pupil
- double vision after a head injury, or with weakness, face drooping or slurred speech
- double vision with loss of vision in one or both eyes
Book an eye examination soon if:
- double vision comes and goes
- double vision appears when you are tired, reading or looking in one direction
- you see double with one eye and it does not clear with blinking or artificial tears
- you are an adult and one eye has started to turn
If you already have a diagnosis, such as a long-standing squint with double vision, and want an opinion on surgery, you can send your reports and scans for review before you decide on travel.
Frequently asked questions
Diplopia is the medical word for double vision: seeing two images of one object. It can affect one eye (monocular) or appear only when both eyes are open (binocular), and it can be constant or intermittent.
Often it is not, but it should always be checked. The NHS says double vision is not usually serious but needs checking even if it comes and goes. In adults, double vision with both eyes open can be a sign of a more serious condition, and sudden double vision needs urgent medical help.
It is usually a problem in the eye itself: dry eye, astigmatism, a cataract or keratoconus, according to AAPOS and the NHS. If the double image stays when you cover the other eye, tell your eye doctor, who will check your glasses prescription and examine the front of the eye.
Because the eyes are not pointing in exactly the same direction, so the brain receives two different pictures. The most common cause is a squint, due to an eye-muscle or nerve problem. In adults the brain cannot suppress the second image the way a child's can, so double vision appears.
Sometimes it comes and goes, but do not assume it will pass. The NHS recommends a check even when double vision is intermittent, because the cause needs to be found and some causes need treatment.
In many cases, yes. Depending on the cause, treatment can be glasses, artificial tears, patching, prism glasses, eye exercises or botulinum toxin injections. Surgery is considered when these do not give enough relief.
Yes. The AAO says it is never too late to treat strabismus, and AAPOS says eyes can be straightened at any age. Prof. Dr. Ahmet Satıcı assesses adults for squint surgery.
It can, because depth perception (stereopsis) depends on both eyes working together. When the eyes are misaligned, that teamwork is disturbed; AAPOS notes that surgery can improve depth perception.
Sources for the facts on this page
- NHS. Double vision. https://www.nhs.uk/conditions/double-vision/
- NHS. Squint. https://www.nhs.uk/conditions/squint/
- NHS. Myasthenia gravis. https://www.nhs.uk/conditions/myasthenia-gravis/
- NHS. Temporal arteritis (giant cell arteritis). https://www.nhs.uk/conditions/giant-cell-arteritis/
- NHS. Stroke: symptoms. https://www.nhs.uk/conditions/stroke/symptoms/
- AAPOS. Diplopia (glossary). https://aapos.org/glossary/diplopia
- AAPOS. Strabismus surgery (glossary). https://aapos.org/glossary/strabismus-surgery
- AAPOS. Adult strabismus. https://aapos.org/patient/patient-resources/adult-strabismus-new
- American Academy of Ophthalmology. Adult strabismus. https://www.aao.org/eye-health/diseases/adult-strabismus
- EyeWiki (AAO). Strabismus Surgery Complications. https://eyewiki.org/Strabismus_Surgery_Complications
- MedlinePlus. Vision problems and double vision: emergency care, eye tests. https://medlineplus.gov/ency/article/003029.htm
Double vision from a squint? Send us your reports.
Send us your eye report or scans. Prof. Dr. Ahmet Satıcı will review them and tell you whether squint surgery or another treatment may suit your eyes, with no obligation. If your double vision started suddenly, get urgent medical help where you live first.
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