Double vision occurs when a person sees a double image where there should only be one. The two images can be side by side, on top of one another, or both. It can happen for many reasons, including diabetes and a blow to the head.

Double vision can affect balance, movement, and reading ability.

Binocular double vision only occurs when both eyes are open. If a person closes one eye, the double vision will go away, as it is caused by each eye seeing slightly differently.

Monocular double vision may occur when the double vision results from an issue with just one eye.

Treatment of double vision depends on the cause and type. Treatments can include eye exercises, specially designed glasses, and surgery.

This article looks at the causes, diagnosis, and treatment of double vision.

Fast facts on double vision

Here are some key points about double vision:

  • Double vision, or diplopia, can result from a range of underlying conditions.
  • Diplopia can affect just one eye or both.
  • A childhood squint, or eye turn, can sometimes recur and cause double vision.
  • Alcohol or recreational drugs can cause temporary double vision.
  • Treatments can include surgery, eye exercises, or corrective lenses.
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Double vision or diplopia is an eye problem that causes a person to see two separate images of the same object.

One of the images is fainter and is called a “ghost image.” People often mistake diplopia for blurred vision.

Diplopia can affect one or both eyes. In monocular diplopia, the double image persists even if the other eye is closed. The cause for this is often in the eye and unlikely because of a neurological problem.

A person with binocular diplopia sees two images only when both eyes are open. More serious conditions may cause this. Diplopia can be horizontal, vertical, or both (diagonal).

Each year, diplopia results in around 850,000 visits to healthcare professionals in the United States. Approximately 95% are outpatient and nonserious, while about 16% are potentially life threatening.

What a person with diplopia sees depends on the type they have.

  • Horizontal: The double image appears side by side.
  • Vertical: One image appears on top of the other.
  • Diagonal: The images are horizontally and vertically displaced from each other.

Poor alignment causing double vision can easily be noticeable. However, sometimes, it may not be apparent and may appear when people move their eyes in a certain direction.

A person can have double vision and not know it. The brain disregards the images from one eye (suppression) to remove mismatching images.

Each eye creates its own image of the environment. The brain combines the representations from each eye and perceives them as one clear picture. The eyes must work together to create depth perception.

Anything that disrupts this process can cause diplopia. It can be nerve or muscle damage.

Certain illnesses can weaken the muscles moving the eyes and produce double vision. Damage to the muscles that move the eyes or the nerves that control eye movement can create a double image.

Damage in specific parts of the eye, like the lens or cornea, can also cause diplopia.

Causes of binocular double vision

A common cause of binocular double vision is a squint or strabismus.

This condition occurs when the eyes are not correctly aligned. Strabismus is relatively common in children. However, the condition does not always result in double vision.

Strabismus causes the eyes to look in slightly different directions.

This condition might be because the affected eye has the following difficulties:

  • they are paralyzed or weak
  • they have restricted movement
  • they are too strong or overactive
  • the nerves controlling the eye muscles have abnormalities

Sometimes, a squint can return later in life for people who had a squint as a child. In some cases, the treatment of a squint can also cause double vision. This occurs because the brain had been suppressing signals from one of the eyes in an attempt to avoid double vision.

Other conditions that can cause double vision include:

  • Thyroid dysfunction: The thyroid gland is in the neck and produces a hormone called thyroxine. Changes in thyroid function can affect the external muscles that control the eye. This includes Graves’ ophthalmopathy, in which the eyes can appear to protrude because fat and tissue build up behind the eye.
  • Stroke or transient ischemic attack: In a stroke or transient ischemic attack, blood fails to reach the brain due to an obstruction in the blood vessels. This can affect the blood vessels supplying the brain or nerves controlling the eye muscles and cause double vision.
  • Aneurysm: An aneurysm is a bulge in a blood vessel, and it can press on the nerve of the eye muscle.
  • Convergence insufficiency: In this condition, the eyes do not work together correctly. The cause is unknown but thought to be due to the neuromuscular ability (the nerves’ control of muscle function) being abnormal.
  • Diabetes: Diabetes can affect the blood vessels that supply the retina at the back of the eye. It can also affect the nerves that control eye muscle movements.
  • Myasthenia gravis: Myasthenia gravis can cause weakness in the muscles, including those that control the eyes.
  • Brain tumors and cancers: A tumor or growth behind the eye can interfere with free movement or damage the optic nerve.
  • Multiple sclerosis (MS): MS affects the central nervous system, including the nerves in the eyes.
  • Black eye: An injury can cause blood and fluid to collect around the eye. This can put pressure on the eye itself or the muscles and nerves around it, causing a black eye.
  • Head injury: Physical damage to the brain, nerves, muscles, or eye socket can restrict the movement of the eye and its muscles.

Causes of monocular double vision

If double vision is noted when one eye is covered but not the other, this is referred to by eye specialists as monocular double vision.

Monocular double vision is less common than binocular double vision.

The following conditions can cause monocular double vision or vice versa:

  • Astigmatism: The cornea, or the transparent layer at the front of the eye, is irregularly shaped. With astigmatism, the cornea has two curves on the surface similar to a football instead of being perfectly round like a basketball.
  • Dry eye: With dry eye, the eye does not produce enough tears or dries out too quickly.
  • Keratoconus: This is a degenerative eye condition that causes the cornea to become thin and cone-shaped.
  • Retinal abnormalities: In macular degeneration, for example, the center of an individual’s field of vision slowly disappears, and sometimes there is swelling, which can cause double vision in one eye.
  • Cataracts: Cataracts occur in more than half of all people in the U.S., ages 80 years and over. It can sometimes cause double vision in one eye.

Temporary double vision

Double vision can sometimes be temporary. Alcohol intoxication and drugs such as benzodiazepines, opioids, or certain anti-seizure medications can sometimes cause this. Head injuries such as concussions can also cause temporary double vision.

Being particularly tired or having strained eyes can bring on temporary double vision. If correct vision does not return quickly, seek medical attention as soon as possible.

Diagnosing double vision can be challenging for an eye specialist because there are many possible causes.

The American Academy of Ophthalmology suggests the first step a specialist will take is asking whether the double vision is monocular or binocular.

If the double vision is monocular, the problem is more likely to be within the eye rather than in the nerves. It is likely to be less serious.

Diagnosis in children

Children cannot always express what they see, which can make diagnosis difficult.

Physical signs of double vision include:

  • squinting or narrowing the eyes to see
  • covering one eye with their hand
  • turning their head in an unusual way
  • looking at objects from the side rather than facing forward

Treatment for double vision will usually depend on the underlying cause.

Treatment for monocular double vision

Treatment varies depending on what is causing monocular double vision, including:

Astigmatism: Corrective glasses or contact lenses can often counteract the curvature and correct the passage of incoming light into the eye.

Laser surgery: This treatment involves reshaping the cornea with a laser.

Cataracts: Surgery is usually the best option. The surgical procedure removes the clouding and the cause of the double vision. Complications include infection, pain, and possibly continued blurry or double vision, but prompt treatment can usually resolve these.

Dry eye: If the eyes do not produce enough tears or dry out too quickly, they can become inflamed and sore. This can result in double vision. Often, a prescription for tear substitute eye drops will relieve symptoms.

Treatments for binocular double vision

Depending on the cause, the treatment for binocular vision varies. Treatments include:

  • wearing glasses
  • eye exercises
  • wearing an opaque contact lens
  • wearing an eye patch
  • surgery on the muscles of the eye to correct their positioning

In certain types of diplopia, botulinum toxin (Botox) may be injected into the eye muscles, causing them to remain relaxed.

However, people should remain cautious of Botox treatment in general, as there are certain contraindications. In a 2019 study, contraindications included neuromuscular disorders such as myasthenia gravis and amyotrophic lateral sclerosis (ALS).

A prism put into glasses can also help to realign the images from each eye. Prisms can be stick-on (temporary) or permanently ground into the lenses. Stick-on prisms are generally reserved for temporary diplopia or when trying different strengths of prism before getting a permanent one.

Eye exercises

Exercises cannot treat many of the conditions that cause double vision. However, some exercises can help with convergence insufficiency.

A 2017 study found that vision therapy improved vision problems, including convergence insufficiency, in people with vision problems caused by a concussion.

Vision therapy is a visual program prescribed by optometrists. It includes eye exercises that aim to develop or improve a person’s visual skills, such as the following:

Smooth convergence

  1. Focus on a detailed target, perhaps a thin stick or small text in a magazine.
  2. Hold the object at arm’s length and at eye level.
  3. Aim for the image to remain as a single image for as long as possible.
  4. Move the target toward the nose in a slow, steady fashion.
  5. When the single image becomes two images, the eyes have stopped working together. Focus intensely on bringing these images back together. Once they join, bring the target closer to the nose.
  6. When unable to rejoin the images, move the hand back to its original position and start the exercise again.
  7. The typical convergence range is 10 centimeters (cm) away from the nose. Aim to keep the image as a single image up to the 10 cm mark.
  8. An orthoptist may provide a tool known as a dot card to assist in these steps.

Jump convergence

  1. Choose a similar target to that in the smooth convergence exercise.
  2. Start the target at a 20 cm distance from the nose.
  3. Fix the gaze on the target for between 5–6 seconds.
  4. Switch to looking at a fixed object around 3 meters (m) away for around 2–3 seconds.
  5. Switch vision back to the nearer target.
  6. A person can repeat this, gradually moving the target closer until they can focus on the object when it is 10 cm away without double vision.

The effectiveness of these exercises is restricted mainly to treating convergence insufficiency. If symptoms do not improve, a person should visit a doctor for further testing.

Read more about exercises for diplopia.

The following are answers to some questions people frequently ask about double vision.

Should I see a neurologist for double vision?

A person who experiences a sudden onset of double vision should contact their healthcare professional. If the healthcare professional cannot identify the cause of the double vision, they may refer the individual to a neurologist for further examination and testing.

Is double vision a red flag?

Neuro-ophthalmologists (doctors who manage vision issues related to the nervous system) state that the sudden onset of double vision is one of the three red-flag symptoms that indicate a person may require assessment by a neuro-ophthalmologist.

The other two red-flag symptoms are a headache accompanied by vision loss and visual loss where other ocular causes have been excluded.

What deficiency causes double vision?

Vitamin B12 deficiency can cause vision issues, such as double vision. Other vitamin deficiencies that can cause double vision include vitamin C and vitamin D.

Diplopia is an eye condition that can occur due to various causes. It may be temporary, but it can also signal a more serious condition.

Treatment for diplopia depends on its cause. An eye doctor can recommend the most appropriate treatment following a thorough evaluation of the person’s diplopia.