Causes of double vision 

Double vision can occur in one eye or both eyes and can be caused by several different conditions.

Double vision in one eye

Double vision in one eye is known as monocular double vision. Double vision continues when the unaffected eye is covered, but you should be able to see normally when the affected eye is covered.

It can be caused by:

  • an irregularly shaped cornea (astigmatism), which is a refractive error
  • dry eye, which is when your eye does not produce enough tears
  • abnormalities of the cornea  
  • abnormalities of the lens, such as cataracts (cloudy patches over the lens) 
  • abnormalities of the retina, such as macular degeneration 

Monocular double vision is rare. Astigmatism and cataracts are the most common causes.

Double vision in both eyes

Double vision that occurs when both eyes fail to work together properly is known as binocular double vision. If you have binocular double vision, your vision will usually be normal if either eye is covered.

If you have binocular double vision, your eyes will point at slightly different angles, causing them to send different images to your brain. The images from each eye are too different for your brain to create a clear, single image. This results in you seeing double images.


squint (strabismus) means your eyes are pointing at different angles. If you have a squint, your eyes do not look in the same direction because some of the muscles that control your eyes are either:

  • weak or paralysed (unable to move)
  • too strong 
  • restricted (prevented from moving) 

Squints are particularly common in young children. Not all squints cause double vision.

A squint can reoccur in someone who had a squint as a child. In some cases, treating the squint and realigning your eyes can result in double vision, as previously your brain may have been ignoring the signals from one of your eyes. When your brain ignores the signals from one eye, this is called suppression.

A reoccurrence of a childhood squint is a common cause of double vision in adults.

Conditions that can cause double vision

In adults, if double vision develops suddenly and is not due to a childhood squint, it may be a sign of another condition affecting the free movement of the eye, the muscles, the nerves or the brain. Conditions may include:

  • a thyroid condition that affects the external eye muscles – your thyroid gland is found in your neck and produces hormones
  • a condition that affects the blood vessels that supply blood to the brain, or to the nerves that control the eye muscles (for example stroke or transient ischaemic attack)
  • diabetes, which can cause double vision by damaging the blood vessels that supply blood to the eye
  • myasthenia gravis, which is a condition that causes the body’s muscles to become weak
  • multiple sclerosis, which is a condition that affects the central nervous system
  • an aneurysm, which is a bulge in a blood vessel that is caused by a weakness in the blood vessel wall
  • brain tumour or cancer behind the eye that prevents free movement or damages the nerves to the eye muscles
  • head injury that damages the brain or the nerves that move the eye muscles, or damages the eye socket and restricts the movement of the eye muscles

Childhood squint

A paediatric consultant explains the causes of squints, a misalignment of the eye. He describes how to identify the symptoms and the treatment options.

Media last reviewed: 09/09/2013

Next review due: 09/09/2015

How your eyes work

Your eyes are made up of: 

  • the cornea and lens at the front of the eye, which act like a camera lens, helping to focus the light coming into the eye 
  • the retina at the back of the eye, which is a light-sensitive layer of tissue that senses light and colour and converts the light that enters the eye into electrical signals 
  • the optic nerve at the back of the eye, which transmits the electrical signals from the retina to the brain, where they are converted into an image

Page last reviewed: 07/01/2013

Next review due: 07/01/2015