Introduction 

Double vision (medically known as diplopia) is seeing two images of a single object. The two images may be one on top of the other, side by side, or a mix of both.

Double vision may be constant, it may come and go, or it may only occur when you're looking in a particular direction.



The cause of your double vision depends on whether your double vision is coming from one eye (monocular) or both eyes (binocular). This also affects which treatment you receive.

Treatment ranges from special glasses and eye exercises, to surgery to remove a cataract.

Recognising double vision in children

Adults are able to describe what is happening with their sight, but young children may not be able to explain what is wrong clearly.

If your child has double vision, they may narrow or squint their eyes closed in an effort to see better, or they may frequently cover one eye with their hand.

They may also turn their head in unusual ways (for example, tilting their head) or look sideways instead of facing forward to try to avoid double vision.

When to see your GP

Visit your GP as soon as possible if you develop double vision or you suspect your child has double vision or a squint.

If you've never had double vision before, it's important to have it checked as it could be a symptom of a serious medical condition.

Your GP will probably refer you to an ophthalmologist (eye specialist) at your local hospital, or an optometrist (optician).

Tests for double vision in hospital

Your eyecare team will usually start by assessing your vision. They may ask you to read letters off a chart, measure any current glasses, look at the position of your eyes, and assess how well you can move them. They may also assess how well your eyes are working together (your binocular vision).

Your ophthalmologist will also use a microscope with a very bright light called a slit lamp to examine the front and back of your eyes.

These results, together with your medical history and any other symptoms you have, should determine what could be causing your double vision.

Further tests

Further tests depend on whether the double vision is monocular or binocular, but may include taking images of your eye. A picture of your brain or eye muscles may also be taken using:



a computerised tomography (CT) scan, which takes a series of X-rays at slightly different angles and uses a computer to put the images together



a magnetic resonance imaging (MRI) scan, which uses a strong magnetic field and radio waves to produce detailed images



Blood tests may also be used to check for an underlying condition.

What causes binocular double vision?

Each eye creates its own slightly different image because the two eyes are physically located in different positions.

However, you usually only see one image. This is because your brain joins the images produced by each eye together into a single image in a process known as fusion.

If your eye muscles or nerves are damaged, the muscles may not be able to control your eyes properly and you may develop double vision.

Your eye muscles can also be weakened as a result of a health condition, or your eyes may not be aligned properly. This is sometimes known as a squint.

Adults who had a squint as a child may sometimes develop double vision over time.

What causes monocular double vision?

Double vision in one eye is known as monocular double vision. You should be able to see normally if the affected eye is covered, but double vision continues when the unaffected eye is covered.

In cases of monocular double vision, the two images are often only slightly separated. This is sometimes referred to as "ghosting".

Causes of monocular double vision can include:



refractive errors – such as short-sightedness or long-sightedness



corneal disease



cataracts



retinal abnormalities



 

Double vision in both eyes

Double vision in both eyes is known as binocular double vision. It happens when both eyes fail to work together properly. If you have binocular double vision, your vision will usually return to normal if either eye is covered.

Physiological double vision

You may experience physiological double vision when objects in your background field of vision, which you're not specifically focusing on, appear double.

Your brain usually compensates for this type of double vision, and it often goes unnoticed. However, children who complain of having double vision sometimes have physiological double vision.

Driving

If you have just developed double vision, or you have other eye-related conditions, your driving ability is likely to be affected. Check with your GP or ophthalmologist (eye care specialist) if you have an eye condition and you're unsure whether it affects your ability to drive safely.

If problems with your vision affect your ability to drive and you hold a current driving licence, it's your legal obligation to inform the Driver and Vehicle Licensing Agency (DVLA). Visit the GOV.UK website to find outhow to tell the DVLA about a medical condition.

Symptoms of double vision 

Double vision is seeing two images of a single object. It's sometimes confused with blurred vision.

If you have blurred vision, a single unclear image will appear. If you have double vision, you'll see two images at the same time. Double vision may be constant, it may come and go, or it may only occur when you're looking in a particular direction.

A weakness in the muscles on either side of your eyeball can cause horizontal double vision, where you see two images side by side while looking to the left or right. It can also cause your eyes to appear "crossed", or as if they are wandering.

Visit your GP as soon as possible if you develop double vision, particularly if you haven't had it before. It could be a symptom of a serious medical condition.

Recognising double vision in children

Adults are able to describe what is happening with their sight, but young children may not be able to explain clearly what is wrong.

If your child has double vision, they may narrow or squint their eyes in an effort to see, or they may frequently cover one eye with their hand. They may also turn their head in unusual ways, or look sideways instead of facing forward.

Sometimes children may also look between the two images. However, they usually quickly learn to ignore one image. This process is called suppression and can lead to permanent loss of vision in that eye(amblyopia).

If you suspect your child has double vision or a squint, take them to see your GP as soon as possible. It's very important the condition is diagnosed and treated quickly.

Causes of double vision 

Double vision can occur in one or both eyes, and can be caused by several different conditions.

Double vision in one eye (monocular)

Double vision in one eye is known as monocular double vision. Double vision continues when the unaffected eye is covered, but you should be able to see normally when the affected eye is covered.

It can be caused by:



an irregularly shaped cornea (astigmatism), which is a refractive error



dry eye, which is when your eye does not produce enough tears



abnormalities of the cornea



abnormalities of the lens, such as cataracts (cloudy patches over the lens)



abnormalities of the retina, such as macular degeneration



The cornea is located at the front of the eye and acts like a camera lens, helping to focus the light coming into the eye.

The retina is a light-sensitive layer of tissue at the back of the eye that converts light entering the eye into electrical signals.

Monocular double vision is rare. Astigmatism and cataracts are the most common causes.

Double vision in both eyes

Double vision caused by both eyes failing to work together properly is known as binocular double vision. If you have binocular double vision, your vision will usually be normal if either eye is covered.

If you have binocular double vision, your eyes will point at slightly different angles, causing them to send different images to your brain. The images from each eye are too different for your brain to create a clear, single image. This results in you seeing double images.

Squints

A squint (strabismus) means your eyes are pointing at different angles. If you have a squint, your eyes don't look in the same direction because some of the muscles controlling your eyes are either:



weak or paralysed (unable to move)



too strong 



restricted (prevented from moving) 



Squints are particularly common in young children. Not all squints cause double vision.

A squint can recur in someone who had a squint as a child. In some cases, treating the squint and realigning your eyes can result in double vision, as previously your brain may have been ignoring the signals from one of your eyes. When your brain ignores the signals from one eye, this is called suppression.

A childhood squint recurring is a common cause of double vision in adults.

Conditions that can cause double vision

In adults, if double vision develops suddenly and isn't caused by a childhood squint, it may be a sign of another condition affecting the free movement of the eye, or the muscles, nerves, or brain. Conditions may include:



a thyroid condition affecting the external eye muscles – your thyroid gland is found in your neck and produces the hormone thyroxine 



a condition affecting the blood vessels supplying blood to the brain, or to the nerves controlling the eye muscles (for example, a strokeor a transient ischaemic attack)



diabetes – which can damage the blood vessels supplying blood to the nerves of the eye muscles



myasthenia gravis – which causes the body's muscles to become weak, including the eye muscles 



multiple sclerosis – which affects the central nervous system, including the nerves of the eye muscles



an aneurysm – a bulge in a blood vessel caused by a weakness in the blood vessel wall, which can press on a nerve of the eye muscle



a brain tumour or cancer behind the eye that prevents free movement or damages the nerves to the eye muscles



a head injury damaging the brain or the nerves that move the eye muscles, or damages the eye socket and restricts the movement of the eye muscles



Diagnosing double vision 

If you have double vision, your GP will probably refer you to an ophthalmologist (eye specialist) at the eye department of your local hospital.

Ophthalmologists commonly work in a team with:

Initial tests

The first step in diagnosing double vision is to establish whether your double vision affects:

Sight tests

Your eyecare team will usually start by assessing your vision. They may ask you to read letters off a chart, look at the position of your eyes, and assess how well you can move them. They may also assess how well your eyes are working together (your binocular vision).

Your ophthalmologist will also use a microscope with a very bright light, called a slit lamp, to examine the front and back of your eyes.

These results, together with your medical history and any other symptoms you have, should determine what could be causing your double vision. 

Further tests

Further tests may include blood tests. A picture of your brain or eye muscles may also be taken using: 



orthoptists – specialists in problems relating to eye movements and how the eyes work together 



optometrists – who carry out eye examinations and assess your need for glasses



both eyes (binocular double vision)



one eye (monocular double vision)



a computerised tomography (CT) scan – this takes a series of X-rays at slightly different angles and uses a computer to put the images together 



a magnetic resonance imaging (MRI) scan – this uses a strong magnetic field and radio waves to produce detailed images



Treating double vision 

If you have double vision, your treatment will depend on whether you have double vision in one eye (monocular) or both eyes (binocular), and the underlying cause.

Underlying conditions may be treated separately.

Double vision in one eye

If you're diagnosed with monocular double vision, treatment will depend on the underlying condition causing the problem.

Astigmatism

If you have monocular double vision caused by astigmatism (an abnormally curved cornea), you may be prescribed corrective lenses, such as glasses or contact lenses. Most children over the age of 12 are able to wear contact lenses.

Corrective lenses compensate for the uneven curve of the cornea so the incoming light that passes through the corrective lens is properly focused on the retina.

Cataracts

If you have monocular double vision caused by cataracts (clouding of the lens), you may need cataract surgery to remove them.

If you have cataracts in both eyes, you'll have them removed on separate occasions to give the first eye time to heal and allow your vision to return.

Cataract operations are common procedures, usually performed as day surgery, which means you should be able to go home shortly afterwards.

Double vision in both eyes

Treatment for binocular double vision also depends on the underlying cause.

Possible treatment options include:

Sometimes children are able to ignore double vision because their brain deals with the problem by ignoring, or "suppressing", one of the two images.

Most squints in children (when the eyes are pointing at different angles) are treated successfully if the condition is detected and treated early. 

Prisms

A prism is a wedge-shaped piece of glass or plastic that bends the light that shines though it. Special prisms called Fresnel (pronounced "frennel") prisms can be attached to your glasses, and are an effective way of treating double vision.

Fresnel prisms are thin, see-through sheets of plastic. One side sticks to the lens of your glasses and the other side has special grooves in it that change the way the light enters your eye.

You may need to wear prisms for several months. The strength can be adjusted to suit your eyes. If the Fresnel prisms are successful, you can have glasses made with prisms built in.

Botulinum toxin

Botulinum toxin (Botox) injections are sometimes used to treat eye movement disorders, such as squints.

The botulinum toxin is injected into one of the muscles controlling the movement of your eye. It blocks the chemical messages sent from the nerves and causes the muscle to relax. This means the muscle can no longer move your eye, and the other muscles take over and straighten the eye.

After the injection, you may experience some temporary side effects, such as:

As the botulinum toxin wears off, you may be able to control the position of your eyes for a period of time. However, this timeframe can vary and further injections may be necessary.

Surgery on your eye muscles

If your double vision is caused by a squint, surgery on your eye muscles can correct the position of your eyes. Any decision to have surgery is made on the basis that the benefit offered by the surgery (usually to align your eyes) is bigger than any risks.

There are six muscles controlling the position of each eye. Each muscle can be weakened, strengthened or moved. Depending on your particular squint, surgery can be carried out on the eye muscles to change the position of your eyes and realign them.

The risks of squint surgery include:

Your eyecare team will discuss the risks and benefits with you.

Opaque intraocular lens

For some cases of double vision, a surgical procedure known as opaque intraocular lens (IOL) may be an option. However, this procedure is only recommended when other treatments have been unsuccessful.

An opaque intraocular lens can only be used to treat people with binocular double vision (both eyes). The procedure usually involves removing the lens of the eye and replacing it with an implant.

Although it's considered a safe procedure, there are risks associated with having an opaque intraocular lens fitted. These include:

Before having an opaque intraocular lens implant, you should discuss the implications of the procedure with your eye specialist. The procedure is irreversible, and removing the implant would involve significant risk of damaging your eye and impairing your vision.



wearing glasses



doing special eye exercises 



fixing prisms on your glasses



wearing an eye patch over one eye



wearing an opaque (not see-through) contact lens in one eye



having botulinum toxin (Botox) injections into an eye muscle



having surgery on your eye muscles



a droopy eyelid (ptosis)



overcorrecting the position of your eye so your eyes are not aligned properly – this can mean your eye "drifts" slightly, and appears as if one eye is looking up or in the opposite direction



worse double vision



making any double vision worse



having a poor result from the operation, which could mean you need further squint surgery – this is estimated to affect around 1 in 10 people who have squint surgery



in rare cases, damaging the eye or your vision – this is estimated to affect 1 in 2,400 people who have squint surgery



the intraocular lens breaking after it has been inserted



damage to the natural lens of the eye (if it is not removed)



inability to examine the back part of the eye (retina)



reduced visual field
 
Double vision