Seeing two separate images of a single object instead of one
- Age, gender, genetics, and lifestyle as risk factors depend on the cause
People with double vision see two images of a single object. The images are separate but often clearly focused. This disorder can have a number of causes, and usually disappears when one eye is closed. You should consult your doctor immediately if you start to experience double vision because it may indicate that you have a serious underlying disorder.
What are the causes?
The most common cause of double vision is weakness or paralysis of one or more of the muscles that control the movements of one eye. The movement of the affected eye is impaired, causing crossed eyes (see Strabismus). Two different views of the same object are received by the visual system and the brain cannot combine them. Tilting or turning the head may briefly correct the problem. However, not all types of crossed eyes cause double vision.
Many serious conditions that affect the brain and nervous system may cause impaired eye movements, leading to double vision. Potential causes include multiple sclerosis, head injuries, brain tumours, and bulging of an artery inside the head due to a weakness in the vessel wall (called an aneurysm). In older people, impaired eye movement resulting in double vision may be linked with diabetes mellitus and, rarely, with atherosclerosis and high blood pressure (see Hypertension). Very rarely, double vision can also occur as a result of a tumour or blood clot behind one of the eyes, causing the movement of that eye to be affected.
How is it diagnosed?
Your doctor may ask you to shut one eye at a time to see whether the double vision disappears. He or she may also ask you to describe the double images, or ask if they appear side by side or one on top of the other or whether one of the images appears to be tilted. Your doctor will probably observe the movements of your eyes closely in order to establish whether any of the eye muscles are weak or paralysed. He or she may also carry out special vision tests to identify weak eye movement.
If double vision has come on suddenly, or if no obvious cause can be found, urgent CT scanning or MRI may be carried out to check for any abnormality in the eye sockets or brain that might be affecting the alignment of the eyes. You may also have a neurological examination.
What is the treatment?
Treatment of double vision is aimed at the underlying cause. A serious disorder such as an aneurysm may need hospital treatment. Double vision due to diabetes mellitus usually disappears over time. If it does not, you may be advised to wear a patch over one eye to eliminate the second image. Surgery to adjust the eye muscles helps if double vision has been present for some time. In some cases, injection of botulinum toxin into an overactive eye muscle may relieve double vision by temporarily paralysing the muscle.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.