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Double vision, the common name for diplopia, is seeing two images of a single object instead of one, for some or all of the time. The two images may be vertically separated (one on top of the other), horizontally separated (side by side), or both. Although we see with two eyes, each of which creates its own, slightly different image, we normally have single vision, meaning we see only one image of an object. This is because your brain can normally control the muscles that move each eye carefully so that both are pointing accurately at the object you are looking at. When each eye produces its own image, your brain then joins them together into one. This gives us what is called single binocular vision.

Alternative Names of Diplopia are: Vision Impairment; Impaired vision; Blurred vision; Double vision.

Causes of Diplopia
Most double vision is binocular. This means that your eyes are pointing at slightly different angles. The result is that each eye sends a significantly different image to your brain. The images from each eye are too different for your brain to create a single clear image, so you see a double image of the object instead. The most common reason for your eyes to point at different targets is a type of squint called strabismus. It is especially common in children. If you have strabismus, your eyes don't look in exactly the same direction because some of the muscles that control your eyes are weak or paralysed. Not all squints cause vision. Binocular double vision that appears suddenly for the first time in teenage or adult life is likely to be a sign of disease. Conditions that can cause binocular double vision include:

  • thyroid disease that affects the external eye muscles,
  • disease of the arteries that supply blood to the brain,
  • diabetes,
  • multiple sclerosis,
  • aneurysm (bulging) of the brain arteries
  • a blood clot behind the eye that prevents normal eye movement,
  • stroke, and
  • Brain tumor, or cancer, in or behind the eye, which distorts the image the eye produces.

A head injury that damages the muscles of the eye sockets or the nerves that control these muscles can result in binocular vision. Monocular double vision is rare. The most common cause is an unusual type of cataract (a clouding of the lens of your eye) that splits the affected eyes image. Other causes include:

  • astigmatism - an abnormal curving of your cornea (the clear part of the eye covering the iris and pupil),
  • dry eye - when your eye does not produce enough tears,
  • a mass or swelling in your eyelid - this can press on the front of the eye,
  • an abnormality in your eye - such as a dislocated lens, and
  • myasthenia gravis - a condition in which your muscles become weak and ineffective due to your immune system attacking them by mistake.

Signs & Symptoms of Diplopia

Symptoms of diplopia include:

  • Eyes appear "crossed," misaligned, or wander.
  • Double vision

The symptoms described above may not necessarily mean that you have diplopia.

Diagnosis of Diplopia

  • Your doctor will refer most cases of double vision to an eye specialist (ophthalmologist) at the eye department of your local hospital.
  • The first step in diagnosis is to determine whether your double vision is monocular or binocular. Your doctor will ask you to cover one eye and then the other to see whether your double vision disappears when one of your eyes is covered.
  • If you have monocular double vision your doctor will examine you for conditions such as cataracts that could be causing the problem. If you have binocular double vision your doctor will test to see which eye muscles are affected. To do this, they will ask you to look at their finger as they move it up, down, left and right. This lets them see how far your eye can move in each direction. They will also cover first one of your eyes, and then the other, while you focus on a target.
  • If your eyes shift as the eye cover is removed, it means your eyes are not aligned properly. A prism (a pieces of glass that bends light) may be placed in front of each eye in turn to shift the image you see, and then the test repeated. The prism allows your doctor to measure the degree of your double vision when you are looking in different directions.
  • Your doctor will use the results of this examination, together with your medical history and any other symptoms you have, to determine what medial condition could be causing your double vision. They will then arrange for you to have the appropriate tests for that condition.

Treatments of Diplopia

Treatment for double vision will depend on the cause.

Squints causing double vision can be corrected by wearing prescription glasses, eye exercises, surgery, or a combination of the three. For most children with double vision caused by squint, the outlook is excellent if the condition is detected and treated early.

It is much more difficult to correct double vision caused by a squint if it continues into adult life. By then your brain may have learnt to see independently with each eye and may no longer be able to fuse the two pictures into one. In this case, your brain normally copes with the problem by suppressing, or forgetting, one of the two images. The result is that your double vision does disappear, but your ability to judge depth in what you see will be badly affected.

How long your double vision lasts will depend on its cause. For example, over time cataracts may begin to cause double vision, but can be corrected immediately with surgery.

Diabetes can cause double vision by damaging the nerves that control eye movement. However, the damaged nerves often re-grow after several months and as they do, your double vision will gradually disappear.

People with astigmatism can wear special contact lenses that correct the double vision immediately.

Prevention of Diplopia

  • Most forms of double vision cannot be prevented, but some causes of double vision can be guarded against.
  • To help reduce the risk of double vision caused by head injury, you should make sure you wear a seatbelt while driving and wear protective goggles and head protection during sporting activities.
  • If you are diabetic you have less chance of developing double vision if you keep your blood sugar carefully under control.

When to seek Medical Advice

Symptoms of diplopia include:

  • Eyes appear "crossed," misaligned, or wander.
  • Double vision

The symptoms described above may not necessarily mean that you have diplopia. However, if you experience one or more of these symptoms, contact your eye doctor for a complete exam.


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