Double vision

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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 â€˜single binocular visionâ€™.

Double vision can be an effect that you can create yourself. For example, if you hold your finger in front of your eyes and then look past it into the distance, you will experience double vision. This is normal.

Double vision and blurred vision are often thought to be the same, but they are not. In blurred vision, a single image appears unclear. In double vision, two images are seen at the same time.

There are two types of double vision: monocular and binocular.

Monocular diplopia is double vision in only one eye. This type of double vision continues even when you completely cover the unaffected eye. If you cover the eye with the double vision you should be able to see normally.

Binocular diplopia is double vision that is produced by both eyes failing to work together properly. This type of double vision will stop if either eye is covered.

You should visit your GP if you have double vision. For adults who have never had double vision before, it is particularly important that you contact your GP immediately, as it can be a symptom of a serious medical condition.