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Causes of Double vision
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 double 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 tumour, 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 double 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 eye’s 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, and
- an abnormality in your eye, such as a dislocated lens.
