If double vision affects just one eye, it is monocular. If it affects both eyes, it is binocular. Treatments depend on the cause and type, but they include eye exercises, specially designed glasses, and surgery.
This article will look at the possible causes, diagnosis, and treatment of double vision.
Here are some key points about double vision. More detail is in the main article.
- Double vision, or diplopia, can result from a range of underlying conditions.
- Diplopia can affect just one eye or both.
- A childhood squint, or eye turn, can sometimes recur and cause double vision.
- Temporary double vision can be caused by alcohol or other recreational drugs.
- Treatments can include surgery, eye exercises, or corrective lenses.
What is double vision?
Double vision can be caused by a number of conditions.
Double vision, or diplopia, is when a person sees a double image. It may affect one eye or both.
It can develop for a number of reasons, and treatment will depend on the cause, which may be minor or serious. Any instances of double vision should be checked by a doctor sooner rather than later.
Other than the obvious difficulties of navigating the world while viewing a double image, double vision can also affect balance, movement, and reading ability.
Each eye creates its own image of the environment. These two representations are combined by the brain so that they are perceived as one clear picture.
If damage occurs to the muscles that move the eyes or the nerves that control that movement, a double image can be created.
Both eyes must work together to create depth of field.
Alternatively, the muscles moving the eyes can become weakened by certain illnesses and produce double vision.
Causes of binocular double vision
A common cause of binocular double vision is a squint or strabismus. This happens when the eyes are not properly aligned. Strabismus is relatively common in children. However, it does not necessarily result in double vision.
Strabismus causes the eyes to look in slightly different directions. This might be because the affected eye muscle or muscles:
- are paralyzed or weak
- have restricted movement
- are too strong
- have abnormal nerves controlling them
Sometimes, a squint can recur in people who had a squint as a child. In some cases, the treatment of a squint can actually cause double vision, despite the individual's vision being normal before the squint was treated. This is because the brain had been suppressing signals from one of the eyes in an attempt to maintain normal vision.
Other conditions can cause double vision include:
Certain thyroid problems can cause double vision.
- Thyroid: The thyroid gland is situated in the neck and produces a hormone called thyroxine. Changes in thyroid function can affect the external muscles that control the eye. This includes Grave's ophthalmology, in which the eyes can appear to protrude because fat and tissue build up behind the eye.
- Stroke or transient ischemic attack (TIA): Blood vessels supplying the brain or nerves controlling the eye muscles can be affected.
- Aneurysm: An aneurysm is a bulge in a blood vessel. This can press on the nerve of the eye muscle.
- Convergence insufficiency: In this condition, the eyes do not work together correctly. The cause is unknown, but it is thought to be due to the muscles that control the eye not lining up properly.
- Diabetes: This can affect the blood vessels that supply blood to the retina at the back of the eye.
- Myasthenia gravis: This can cause weakness in the body's muscles, including those controlling the eyes.
- Brain tumor/cancer: A tumor or growth behind the eye can interfere with free movement or damage the eye's nerves.
- Multiple sclerosis: A disease that affects the central nervous system, including nerves that supply the eyes.
- Black eye: An injury can cause blood and fluid to collect around the eye. This can press on the eye itself or the muscles and nerves around it.
- Head injury: Physically damaging the brain, nerves, muscles, or eye socket can restrict the movement of the eye and its muscles.
Causes of monocular double vision
If double vision is noted when one eye is covered and not when the other eye is covered, this is referred to as monocular double vision.
Monocular double vision is less common than binocular double vision and can be caused by the following conditions:
- Astigmatism: The cornea is irregularly shaped (the transparent layer at the front of the eye). This causes a refractive error; in other words, the light is bent more, or less, than it should be.
- Dry eye: The eye does not produce enough tears, or it dries out too quickly.
- Keratoconus: This is a degenerative condition of the eye that causes the cornea to thin and become cone-shaped.
- Abnormality of the lens: This includes cataracts, are cloudy patches over the lens.
- Abnormality of the retina: In macular degeneration, for example, the center of an individual's field of vision slowly disappears.
- Cataracts: Cataracts affect more than half of Americans over the age of 80 years and can sometimes cause double vision in one eye.
Temporary double vision
Sometimes, double vision can be temporary. This is often caused by alcohol intoxication, benzodiazepines, opioids, or certain types of drugs for seizures and epilepsy. Head injuries, like concussions, can also cause temporary double vision.
Being particularly tired or having strained eyes can bring on temporary double vision. If normal vision does not come back quickly, medical attention should be sought as soon as possible.
Diagnosing double vision can be challenging for an ophthalmologist or optometrist (eye specialists) because there are so many possible causes.
An article on the American Academy of Ophthalmology's website states:
"The patient who complains of double vision can have something as benign as dry eye or as life-threatening as an intracranial tumor. The cause may be as rare as Wernicke encephalopathy or as common as convergence insufficiency."
The first question a specialist will ask is whether the double vision is monocular or binocular.
If the double vision is monocular, it means that the problem is more likely to be within the eye, rather than in the nerves. It is likely to be less serious.
Diagnosis in children
Children cannot always express what they are perceiving, and this can make diagnosis difficult.
Things to watch out for include:
- squinting or narrowing the eyes to see
- covering one eye with their hand
- turning their head in an unusual way
- looking at objects from the side rather than facing forward
- flicking eyes side to side, between images
This will depend on the underlying cause.
Treatment for monocular double vision
Treatment will depend on the cause.
Astigmatism refers to an abnormally curved cornea. Corrective glasses or contact lenses often can counteract the curvature and correct the passage of incoming light into the eye.
Laser surgery is another option. This treatment involves reshaping the cornea with a laser.
Cataracts: Surgery is usually the best option. The surgical procedure removes the clouding and the cause of the double vision. Complications include infection, pain, and blurry or double vision, but prompt treatment can usually resolve these.
Dry eye: If the eyes do not produce enough tears or dry out too quickly, the eyes can become inflamed and sore. This can result in double vision. Often, a prescription for tear substitute eye drops will relieve symptoms.
Treatments for binocular double vision
Depending on the cause, the treatments for binocular vision vary, but they include:
- wearing glasses
- eye exercises
- wearing an opaque contact lens
- fixing thin, plastic, see-through prisms to glasses
- botulinum toxin (Botox) injections into the eye muscles cause them to remain relaxed
- wearing an eye patch
- surgery on the muscles of the eye to correct their positioning