What Is Double Vision? What Is Diplopia? What Causes Double Vision?

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Main Category: Eye Health / Blindness
Article Date: 11 Nov 2009 - 6:00 PST

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Double vision, also known as Diplopia, is the simultaneous perception of two images of a single object - the patient sees two images of a single thing either all the time, or some of the time. The displacement may be horizontally, vertically or diagonally. Diagonal double displacement (double vision) means both the horizontal lines and vertical lines are being perceived as doubled - also known as oblique separation.

Single binocular vision - each eye of the individual works independently, creating its own, faintly different image. The patient, however, only perceives one image because the brain is able to control the muscles of the eyes so that both of them point accurately at the object the person is looking at. The brain then joins the images produced by both eyes into one image - this is known as single binocular vision.

If, however, the eye muscles are damaged, or even the nerves, or if some health condition has weakened them, the muscles may not be able to control the eyes correctly, resulting in double vision.

According to Medilexicon's medical dictionary, diplopia is: "The condition in which a single object is perceived as two objects."

There are three types of double Diplopia:

• Binocular double vision - both the patient's eyes do not work together properly. The double vision will disappear if the patient covers one eye, or the other.


• Monocular double vision - this is when double vision continues when the unaffected eye is covered. The double vision comes from just one eye. When the affected eye is covered, the double vision usually disappears. Ghosting is common with patients with monocular double vision - the two images are usually only very slightly separated.


• Physiological double vision - often objects the person is not focusing on - background objects - appear doubled. This vision problem often goes unnoticed because the patient's brain can usually compensate for this type of double vision. When a child complains of double vision, it is usually physiological double vision.

It is important that patients with double vision check with their GP (general practitioner, primary care physician) or ophthalmologist about the effects their vision defect may have on their vehicle driving competence. In the UK, and many other countries, people with any vision defect who hold a current driving license are legally required to inform the authorities of their condition.

What are the signs and symptoms of double vision?

A symptom is something the patient feels and reports, while a sign is something other people, including a doctor or nurse may detect. For example, pain may be a symptom while a rash may be a sign.

Double vision, which is sometimes confused with blurred vision, as mentioned above, is when the individual sees two images of a single object. Blurred vision is a single unclear image, while double vision is the perception of two images, when there is only one.

Double vision affects people in different ways. Some patients may experience double vision occasionally, while others have it all the time. Some people say they only experience double vision when they are looking in a specific direction.

If an individual gets double vision when they see in one particular direction, it is most likely due to eye-muscle weakness - either the lateral rectus muscle or the medial rectus muscle. Both muscles are located on either side of the eyeball - their movements make the eyeball move to the left or right.

Patients with muscle paralysis may have a cross-eyed, or wandering eye appearance.

Anybody who develops double vision should see either their GP or an ophthalmologist immediately. Double vision is a sign of several possible medical conditions, some of which may be serious.

Double vision in children

Children are less able to express what is wrong with their eyesight than adults. A child with double vision may narrow their eyes when trying to focus on something (squint). Some kids may cover one eye with their hand, or deliberately close one eye. If a child gazes at things with an unusual head position frequently it could be a sign of double vision.

Childhood double vision can be treated more effectively if diagnosed early on. Therefore, any signs or symptoms of double vision in a child should be reported to a health care professional as soon as possible.

What are the causes of double vision?

• Binocular double vision - most people with double vision have binocular double vision. The patient's eyes are not perfectly aligned - they point at slightly different angles, which results in slightly different images being sent to the brain. However, the images are not similar enough for the brain to create one single, clear image - so, two images are created (double image, double vision).
  
  The most common reason for eyes not being completely aligned is a squint (strabismus). This is due to a weakened or paralyzed eye muscle. Not all squints cause double vision, but most cases of double vision are caused by squints. Squints are common among young children.
  
  The following conditions can cause binocular double vision:
  
  
  • A thyroid disease, which results in weakened external eye muscles.
  
  
  • An arterial disease. Especially one involving an artery which feeds the brain with blood and essential oxygen.
  
  
  • Diabetes. The nerves that control eye movement may be damaged. If the diabetes is controlled (treated effectively) the damaged nerves usually repair themselves and the problem resolves.
  
  
  • Myasthenia gravis - this is an autoimmune neuromuscular disorder in which the muscles become fatigued and exhausted.
  
  
  • MS (multiple sclerosis) - the central nervous system (CNS) is attacked by the person's own immune system. That is why MS is known as an auto-immune disease. The CNS includes the brain, spinal cord and optic nerves.
  
  
  • An aneurysm - occurs when part of a blood vessel (artery) or cardiac chamber swells, - either the blood vessel is damaged or there is a weakness in the wall of the blood vessel. As blood pressure builds up it balloons out at its weakest point. The swelling can be quite small or very large - when large it tends to extend along the blood vessel. As the aneurysm grows there is a greater risk of rupture - this can lead to severe hemorrhage, and other complications, including sudden death. If the arteries in the brain bulge there is a risk of developing double vision.
  
  
  • A blood clot - if this develops behind the eye, eye movement may become restricted.
  
  
  • A stroke - a condition where a blood clot or ruptured artery or blood vessel interrupts blood flow to an area of the brain. A lack of oxygen and glucose (sugar) flowing to the brain leads to the death of brain cells and brain damage, often resulting in impairment in speech, vision, movement, and memory.
  
  
  • Cancer - a tumor in or behind the eye may distort the image the eye produces. A brain tumor may also be a cause of double vision.
  
  
  • Injury - head injuries can sometimes result in damage to the muscles in the orbit (eye socket), or the nerves that control eye-movement muscles, both of which can result in double vision.
  
  


• Monocular double vision - this less common form of double vision can be caused by the following abnormalities:
  
  
  • An abnormality in the cornea
  • An abnormality in the iris
  • An abnormality in the lens of the eye
  • An abnormality in the vitreous humor; a gelatinous substance that fills the eye.
  • An abnormality in the aqueous humor; a watery fluid that fills the space behind the cornea.
  
  Monocular double vision is commonly caused by:
  
  
  • Astigmatism - the front surface of the eye (cornea) of a person with astigmatism is not curved properly - the curve is irregular - usually one half is flatter than the other - sometimes one area is steeper than it should be.
  
  
  • A cataract - a rare type of cataract may cause the eye's image to be split. Cataracts are cloudy areas in the lens inside the eye - which is normally clear.
  
  and also (less commonly)..
  
  
  • Dry eye
  
  
  • A swelling in the eyelid that presses against the front of the eye.
  
  
  • A dislocated lens


• Temporary double vision may be caused by:
  
  
  • Alcohol intoxication
  • Concussion
  • Anti-epileptic drug side effect. Such drugs as Phynytoin and Zonisamide.
  • Anti-convulsant drug side effect. An example includes Lamotrigine.
  • Hypnotic drug side effect. Zolpidem.
  • Tiredness, especially if the eye muscles are strained.

How is double vision diagnosed?

A doctor who specializes in vision and eye conditions and diseases is called an ophthalmologist. If you go to your GP with what appear to be signs and symptoms of double vision, you will most likely be referred to an ophthalmologist.

• Preliminary tests - the specialist will first try to determine whether the patient has monocular or binocular double vision. The patient will be asked to cover one eye and then the other and describe his vision.


• Binocular double vision - the specialist needs to determine which eye muscles are faulty. Typically, the patient will be asked to visually follow the doctor's finger as it moves horizontally and vertically - this simple test will tell the doctor how far each eye can move.


• Covering one eye - with one eye covered the patient is asked to focus on an object. If, when the cover is removed, the eyes change alignment, it is an indication of an alignment problem.


• Prism - a prism is a piece of glass that bends light. A prism is placed in front of one eye - the prism shifts the image the person is looking at. Then the prism is placed in front of the other eye. This test helps the doctor determine the degree of double vision experienced by the patient when he/she is looking in various directions.


• Monocular double vision - the specialist will examine the patient for possible eye conditions, such as cataracts. With data from the patient's medical history, signs and symptoms and the test results, the doctor will determine what medical condition has caused the double vision. The next step is to order tests for that condition.

What are the treatment options for double vision?

Treatment for double vision depends on what type it is: binocular or monocular.

• Binocular double vision treatment - treatment options will depend on several factors, including its cause and prognosis. Treatment may include:
  
  
  • Eye muscle surgery
  • Having a contact lens in one eye which totally blocks vision
  • Having an eye patch over one eye
  • Receiving a botulinum toxin injection for one of the eye muscles
  • Wearing glasses with filters
  
  Children's brains are better able to suppress one of the images, resulting in ignored double vision (the double vision is there, but the brain manages to ignore some of the data so that the patient experiences no symptoms).


• Strabismus (squint) - treatment may involve eye exercises, special glasses, surgery, or a combination, which sometimes may include all three.
  
  If the fault is detected early on during childhood the chances of a total cure are very good. If a squint continues into adult life double vision is much harder to correct.
  
  Botulinum toxin injections may be utilized to treat squints, and some other eye disorders. Small-dose botulinum toxin injections may stop muscle spasms by preventing chemical messages in the nerves. The botulinum toxin is mixed with salt water and injected into the muscle. The patient may feel a bit sore afterwards, but recovery is fast.


• IOL (opaque intraocular lens) - this procedure may be carried out if the patient has not responded well to other treatments. IOL is only used for patients with binocular double vision. The lens of the eye is removed and replaced with an implant.
  
  The lens may be removed in fragments (Phacoemulsification). The lens may be removed in one piece (extracapsular surgery). An incision is made in the cornea and the IOL is inserted.
  
  An iris claw lens (specially made tinted IOL) may be surgically attacked to the tissue of the iris using a claw-like mechanism. With this procedure the natural lens of the eye is not removed.
  
  Although the IOL procedure has a good success rate, there is a slight risk of the intraocular lens breaking, or damaging the natural lens.


• Monocular double vision - treatment will depend on the underlying condition that is causing monocular double vision.
  
  
  • Astigmatism - the patient may be prescribed corrective lenses, which may be in the form of glasses or contact lenses. Contact lenses are not normally prescribed for children 12 years of age or younger. The corrective lenses make up for the uneven curvature of the cornea, so that rays of light properly focus on to the retina.
    
    Patients with astigmatism may also benefit from laser surgery.
  
  
  • Cataracts - the patient will undergo surgery to have the cataracts removed. If the patient has cataracts in both eyes he/she will undergo two separate operations, one for each eye. The second operation will occur after the first eye has healed.


• Dry eye syndrome (keratoconjunctivitis sicca) - the eyes do not make enough tears, or they dry out too rapidly. The eyes dry out, become sore and inflamed, often resulting in double vision. The patient will be prescribed tear substitutes (eye drops). In very severe cases the patient may need surgery, but this is very rare.

Prevention

There is nothing people can do to prevent double vision if they have a squint or astigmatism. However, there are steps people can take to prevent or effectively treat underlying causes which increase the risk of double vision.

• Diabetes - patients with diabetes who adhere to treatment protocols have a lower risk of developing double vision, compared to diabetes patients who don't. In other words, if you keep your diabetes under control your risk of double vision is much lower than if you don't.
  
  Diabetes Type II can develop as a result of lifestyle. People who eat a healthy and balanced diet, do plenty of exercise and maintain a healthy bodyweight are much less likely to develop diabetes, and subsequently double vision, compared to people who are obese, do not eat healthily and are physically inactive.


• Cataracts - if you protect your eyes from sunlight by wearing sunglasses, don't smoke, eat a healthy balanced diet, your risk of developing age-related cataracts will be significantly lower, compared to a person who smokes regularly and does not protect his/her eyes from sunlight.


• Dry eye syndrome - keeping your eyes well lubricated will help prevent double vision. If you spend a long time each day in front of a computer monitor, make sure it is properly positioned. Avoid smoke and other eye irritants and try to minimize eye strain.


• Head injuries - wearing a seatbelt in a car, wearing a good helmet when you are on a motorbike, wearing appropriate headgear and goggles when using certain types of machinery or playing some sports, will help protect your head. These preventive measures will lower your risk of developing double vision from a head injury.

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today