Double vision is caused by a number of different conditions, some of which can be serious. If you are experiencing double vision, whether it is intermittent or constant, visiting an optometrist should help you reach a diagnosis. Known medically as diplopia, double vision is when you see two versions of a single object. The images may overlap, sit side by side or a mixture of the two. The condition can be present in one eye or both eyes, which often guides the diagnosis. Here are some of the common causes for both types of double vision. Double vision in one eyeYou should be able to self-diagnose whether you have double vision in just one eye, as simply covering the affected eye will return your eyesight to normal. However, you will still have double vision if the unaffected eye is covered. This condition, called monocular double vision, is rarer than when it occurs in both eyes. Some common causes include:

• Astigmatism - an irregularly-shaped cornea
• Cataracts· Macular degeneration - this typically occurs in both eyes, but may be more prominent in one eye in the earlier stages
• Dry eye.

Double vision in both eyes

When the condition presents in both eyes, it's called binocular double vision. This means your eyesight should return to normal regardless of which eye you cover. Typically, this is caused by your eyes pointing in different directions, which sends images to the brain that are harder to merge into a clear, single image. Therefore, a squint is the most common cause of double vision. However, squints are usually present from a young age, so if double vision presents suddenly as an adult and you have not previously had a squint, there could be an underlying reason.

Some conditions that cause sudden double vision are serious, emphasising the importance of visiting an optometrist as soon as possible.

• Diabetes can damage the blood vessels that supply blood to the brain and the nerves that control the eye
• Multiple sclerosis is a condition that affects the body's central nervous system
• Brain tumours and cancer of the eye can also cause double vision by damaging the nerves in the eyes' muscles
• Head injuries could damage the brain or eye socket
• Thyroid conditions can affect eye muscles
• Aneurysms are bulges in blood vessels that occur when the wall of the blood vessel becomes weak
• Strokes or other conditions can affect blood flow to the brain.