Double Vision (Diplopia)

Monocular vs binocular double vision

Causes of binocular double vision

The two eyes must point at exactly the same target. Six muscles move each eye, controlled by three cranial nerves (the third, fourth and sixth). Anything that weakens, restricts or misdirects these muscles makes the eyes point in slightly different directions.

Cranial nerve palsies

• Third nerve palsy: drooping eyelid, eye turned down and out, sometimes a dilated pupil. A third nerve palsy with a dilated pupil can mean an aneurysm and is an emergency.
• Fourth nerve palsy: vertical or tilted double vision, worse looking down (for example on stairs). People often tilt their head to compensate. Common after head injury.
• Sixth nerve palsy: side-by-side double vision, worse looking into the distance and toward the affected side.

In adults over 50, the most common cause of an isolated nerve palsy is reduced blood supply to the nerve from diabetes or high blood pressure. These "microvascular" palsies usually recover within 3 months. See cranial nerve palsy.

Neuromuscular and muscle causes

• Myasthenia gravis: double vision and drooping lids that vary and worsen with fatigue, improving after rest.
• Thyroid eye disease: swollen, stiff eye muscles, often with bulging eyes, redness and grittiness. Usually with Graves' disease.
• Orbital injury: a blow-out fracture can trap an eye muscle, causing double vision when looking up.

Brain causes

• Stroke or transient ischemic attack in the brainstem
• Multiple sclerosis, especially in younger adults
• Raised pressure inside the skull, from a tumor or idiopathic intracranial hypertension, causing sixth nerve palsy
• Brain aneurysm pressing on the third nerve
• Head injury

Childhood and long-standing squint

Children with strabismus usually do not see double, because the brain ignores one image. Adults with an old squint can develop double vision if the eyes drift further or after cataract surgery.

Other causes

Alcohol, sedatives, some anti-seizure medicines, extreme fatigue, giant cell arteritis, botulism and Wernicke encephalopathy (from vitamin B1 deficiency in heavy drinkers) can all cause double vision.

Causes of monocular double vision

• Dry eye: a patchy tear film distorts the image; blinking helps
• Astigmatism or an out-of-date glasses prescription
• Cataract: clouding of the lens causing ghosting, often with glare
• Keratoconus: a cone-shaped cornea
• Corneal scarring or previous refractive surgery
• A dislocated lens or problems with an artificial lens

A pinhole held in front of the eye often makes monocular double vision disappear, confirming an optical cause.

How doctors find the cause

Your doctor will ask whether the images are side by side or vertical, whether it changes with direction of gaze or time of day, and about headaches, eyelid droop, weakness, diabetes and thyroid disease. Examination includes the cover test, eye movements in all directions, pupils, eyelids and a full neurological exam.

Tests depend on the findings:

• blood sugar, thyroid tests and inflammatory markers (ESR, CRP)
• acetylcholine receptor antibodies or an ice-pack test for myasthenia
• urgent MRI or CT, and blood vessel imaging, for stroke, aneurysm or a palsy with other neurological signs
• eye exam with a slit lamp for monocular causes

Treatment

Treatment depends on the cause:

• Covering one eye with a patch or frosted lens gives immediate relief from binocular double vision while the cause is treated.
• Prism glasses bend light to realign the images in mild, stable misalignment.
• Treating the cause: controlling diabetes and blood pressure, medicines for myasthenia, steroids or other therapy for thyroid eye disease, urgent stroke or aneurysm care.
• Botulinum toxin injections into an eye muscle for some palsies.
• Strabismus surgery to realign the eyes once things are stable, usually after 6 months.
• For monocular causes: lubricating drops, updated glasses, cataract surgery or specialty contact lenses.

Frequently asked questions

When should I worry about double vision?

Treat new double vision that disappears when one eye is covered as urgent, and get emergency care if it comes with headache, droopy eyelid, weakness, numbness, speech or swallowing problems, or after a head injury. These can signal stroke, aneurysm or myasthenia.

What causes sudden double vision?

Sudden binocular double vision is most often caused by a cranial nerve palsy from diabetes or high blood pressure in older adults. Other important causes include stroke, aneurysm, myasthenia gravis, multiple sclerosis, thyroid eye disease and head injury.

What does it mean if I see double out of one eye only?

Double vision that stays when the other eye is covered is monocular. It is caused by a problem in that eye, such as dry eye, astigmatism, cataract or a corneal irregularity. It is rarely an emergency, but an eye exam is needed.

Can tiredness cause double vision?

Mild double vision when very tired can happen if you have a small, normally controlled eye misalignment. Double vision that worsens through the day with droopy lids and improves with rest is typical of myasthenia gravis and should be checked.

Does double vision go away on its own?

Sometimes. Palsies caused by diabetes or high blood pressure usually improve within 3 months. Double vision from dry eye or fatigue may come and go. However, the cause should always be diagnosed first, as some causes need urgent treatment.