Reviewed by Dr Norhafizah Hamzah, Paediatric Ophthalmologist & Squint Surgeon of OasisEye Specialists | Last updated: July 2026
Have you ever looked at a single object and seen two overlapping copies of it? This is called diplopia, or double vision. It can be alarming the first time it happens, but understanding what causes it — and how treatable it usually is — can make it much less frightening.
What Is Double Vision (Diplopia)?
Normally, each eye sends a slightly different image to the brain, which fuses them into one clear, three-dimensional picture. Double vision happens when that process breaks down — either because the eyes aren’t pointed at the same spot, or because something inside one eye is distorting the image before it even reaches the brain. The first step in figuring out the cause is identifying which of the two main types you have.
Binocular Diplopia vs. Monocular Diplopia
A simple way to tell the two apart: cover one eye at a time.
- If the double vision disappears when either eye is covered, it’s binocular diplopia.
- If the double vision remains even with one eye closed, it’s monocular diplopia — and the problem lies within that specific eye.
Causes of Binocular Diplopia
Binocular diplopia occurs when both eyes are open, and it disappears as soon as one eye is closed. It happens when the images sent by each eye are not similar in position or sharpness for the brain to merge, usually because of strabismus — a misalignment of the eyes, also known as a squint.
Strabismus itself can stem from neurological or mechanical causes, including:
- Cranial nerve palsy
- Brain tumor
- Stroke
- Myasthenia gravis
- Graves’ disease (hyperthyroidism)
- Uncorrected refractive error
Causes of Monocular Diplopia
Monocular diplopia is double vision experienced in just one eye — it persists even when the other eye is closed. Common causes include:
Is Double Vision a Medical Emergency?
Most cases of double vision are not life-threatening, but some are — so it’s worth knowing the warning signs. Seek immediate medical attention if double vision appears suddenly and is accompanied by any of the following:
- Severe headache
- Slurred speech or difficulty understanding speech
- Facial drooping or weakness
- Numbness or weakness on one side of the body
- Loss of balance or coordination
- Eye pain or a bulging eye
- Recent head injury
These can be signs of a stroke, aneurysm, or other neurological emergency, and warrant urgent assessment. Even without these symptoms, any new or persistent double vision — sudden or gradual — should be evaluated by an eye doctor, since it rarely resolves on its own without identifying and addressing the underlying cause.
How Is Double Vision Diagnosed?
If you experience double vision, your eye doctor or optometrist will run a series of diagnostic tests to pinpoint the cause:
- Refraction — measures how light focuses in your eye to check for refractive errors.
- Cover Test — checks for eye misalignment that causes binocular diplopia by observing how each eye moves when the other is covered.
- Comprehensive Eye Examination — to rule out other eye conditions such as, dry eyes, corneal issues, and cataracts.
- CT scan or MRI — used to rule out brain-related causes such as tumors, aneurysms, or stroke.
- Blood Tests — elevated levels of certain antibodies or hormones can point to underlying conditions, such as myasthenia gravis or thyroid eye disease, that affect the eye muscles and nerves.
Treatment Options for Double Vision
Once the cause is identified, treatment is tailored to it. Common approaches include:
- Treating the Underlying Cause — if a condition like a brain tumour, stroke, or diabetes is responsible, treatment focuses on managing that condition first; the double vision often improves as it does.
- Prism Glasses — special lenses that bend light before it enters the eye, realigning the two images into one.
- Vision Therapy — structured eye exercises that can strengthen eye muscles and improve coordination and alignment over time.
- Strabismus Surgery — a procedure to adjust the eye muscles directly, used when misalignment is significant or doesn’t respond to non-surgical options.
Double Vision FAQs
It can be. Most cases are caused by manageable issues like uncorrected refractive error or dry eye, but binocular diplopia in particular can occasionally signal a serious neurological condition such as stroke or a brain aneurysm, so it should always be evaluated promptly.
Occasionally — for example, double vision caused by simple eye strain or fatigue may resolve with rest. However, persistent double vision rarely resolves without treating its underlying cause, so it shouldn’t be ignored.
Binocular diplopia happens only when both eyes are open and disappears when either eye is closed; it’s caused by eye misalignment. Monocular diplopia persists even with one eye closed and points to a problem within that specific eye, such as astigmatism or cataract.
Eye strain and fatigue can cause temporary, intermittent double vision in some people, particularly toward the end of a long day. However, because double vision can also signal more serious conditions, new double vision should still be checked by an eye doctor rather than assumed to be stress-related.
Treatment depends entirely on the cause — it may involve glasses to correct a refractive error, prism lenses to realign images, vision therapy to strengthen eye muscles, management of an underlying condition like thyroid eye disease or diabetes, or strabismus surgery in more significant cases.
Start with an ophthalmologist or optometrist, who can determine whether the cause is within the eye or related to eye alignment and nerve function, and refer you to a neurologist or other specialist if needed.
When to See an Ophthalmologist
Double vision can stem from anything as minor as an uncorrected refractive error to as serious as a neurological disorder — and the only way to know which you’re dealing with is a proper eye examination. With the right diagnosis and care, most people with double vision find relief and regain clear, single vision.
This article is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. If you experience sudden double vision with headache, weakness, slurred speech, or facial drooping, seek emergency medical care immediately.
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