Double vision occurs when a person sees a double picture in which only one should be present. The two pictures may be next to each other, on top of each other or both.
The condition can affect ability to balance, move, and read.
When double vision only affects one eye, this is monocular. When both eyes are affected, then it is binocular. Treatments depend on the cause and form, but eye exercises, specially made lenses, and surgery are included.
The article would look at the causes of double vision, diagnosis and treatment.
Fast facts on 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.
Double vision can be cause by nerve or muscle damage in the eye.
Every eye produces its own surrounding image. The brain integrates and perceives the representations from each eye as one unified image.
A double image can be produced by damage to the muscles that move the eyes or the nerves that regulate eye movement.
To establish depth of field the eyes need to work together.
Some diseases can weaken the muscles that move the eyes, and cause double vision.
Causes of binocular double vision
A common cause of double vision of the binoculars is squint or strabism.
It happens when eyes aren’t matched properly. Strabism is relatively common in adolescents. The disorder does not always lead to double vision though.
Strabism causes the eyes to have a subtly different appearance. It may be because the muscles of the affected eye have the following problems:
- They are paralyzed or weak.
- They have restricted movement.
- They are too strong or overactive.
- The nerves controlling the eyes muscles have abnormalities.
Sometimes, people who have a squint as a child will restore a squint later in life. In certain cases, treating a squint can in fact cause double vision, even if the individual’s vision is fine until the squint is treated.
This is because the brain in an effort to preserve normal vision had blocked the signals from one of the eyes.
Other conditions can lead to double vision including:
- Thyroid dysfunction: The thyroid gland is 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 ophthalmopathy, in which the eyes can appear to protrude because fat and tissue build up behind the eye.
- Stroke or transient ischemic attack (TIA): In a stroke, blood fails to reach the brain due to an obstruction in the blood vessels. This can affect the blood vessels supplying the brain or nerves controlling the eye muscles and cause double vision.
- 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 correctly.
- Diabetes: This can affect the blood vessels that supply the retina at the back of the eye. It can also affect the nerves that control eye muscle movements.
- Myasthenia gravis: This can cause weakness in the muscles, including those that control the eyes.
- Brain tumors and cancers: A tumor or growth behind the eye can interfere with free movement or damage the optic nerve.
- Multiple sclerosis: MS is a disease that affects the central nervous system, including the nerves in the eyes.
- Black eye: An injury can cause blood and fluid to collect around the eye. This can put pressure on the eye itself or the muscles and nerves around it.
- Head injury: Physical damage to the brain, nerves, muscles, or eye socket can restrict the movement of the eye and its muscles.
Causes of monocular double vision
If one eye is shielded but not the other, double vision is observed, this is called monocular double vision.
Single vision monocular is less common than double vision binocular. The following conditions may cause monocular double vision and may be caused by:
- Astigmatism: The cornea, or the transparent layer at the front of the eye, is irregularly shaped. With astigmatism, the cornea has two curves on the surface similar to a football instead of being perfectly round like a basketball.
- 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 become thin and cone-shaped.
- Retinal abnormalities: In macular degeneration, for example, the center of an individual’s field of vision slowly disappears, and sometimes there is swelling which can cause double vision in one eye.
- Cataracts: Cataracts occur in more than half of all people in the United States over the age of 80 years and can sometimes cause double vision in one eye.
Temporary double vision
Often double vision may be temporary. It is commonly caused by drug intoxication, benzodiazepines, opioids, or other anxiety and epilepsy drugs. Head injuries can also cause temporary double vision, such as concussions.
Being particularly exhausted or getting eyes strained can offer temporary double vision. If normal vision does not return soon, seek medical attention at the earliest possible opportunity.
To an eye doctor, diagnosing double vision may be difficult, as there are so many potential causes.
An article from the American Academy of Ophthalmology 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 specialist will begin by asking if the double vision is either monocular or binocular.
When the dual vision is monocular, this means the problem is more likely to be in the eye than in the nerves. This would certainly be less serious.
Diagnosis in children
Children cannot always express what they see, and this can make diagnosis difficult.
Physical signs of double vision 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: An abnormally shaped cornea is referred to here. The curvature can also be counteracted by protective glasses or contact lenses and the passage of incoming light through the eye.
Other choice is Laser surgery. This procedure is for the cornea to be reshaped with a laser.
Cataracts: The safest treatment is usually surgery. The procedure removes the clouding and the double vision trigger. Complications include illness, pain, and likely persistent blurred or double vision, but these may usually be overcome by timely care.
Dry eye: When the eyes don’t get enough tears or dry out too quickly, they can get inflamed and sore. That can lead to double vision. Tear replacement eye drops are also used to alleviate 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
- botulinum toxin (Botox) injections into the eye muscles, causing them to remain relaxed
- wearing an eye patch
- surgery on the muscles of the eye to correct their positioning
A stick-on prism, positioned at the center of the spectacle frame between the eyes, may also allow the images from each eye to realign.
Exercises are unable to treat many of the conditions which cause double vision. However, some exercises can help with the insufficiency of convergence.
- Focus on a detailed target, perhaps a thin stick or small text in a magazine.
- Hold this at eye-level, an arm’s length away from you.
- Aim for the image to remain as a single image for as long as possible.
- Move the target towards the nose in a slow, steady fashion.
- When the single image becomes two images, your eyes have stopped collaborating. Focus intensely on bringing these images back together. Once they join, bring the target closer to the nose.
- Once you become unable to rejoin the images, move your hand back to its original position and start the exercise again.
- The normal convergence range is 10 centimeters (cm) away from the nose. Aim to keep the image as a single image up to the 10cm mark.
- An orthoptist may provide a tool known as a Dot Card to assist these steps.
- Choose a similar target to that in the smooth convergence exercise.
- Start the target at a 20 cm distance from the nose.
- Fix your gaze on the target for between 5 and 6 seconds.
- Switch to looking at a fixed object around 3 meters (m) away for around 2 to 3 seconds.
- Switch your vision back at the nearer target.
- Repeat this, gradually moving the target closer, until you can focus on the object when it is 10 cm away without double vision.
The usefulness of these activities is largely limited to resolving the insufficiency of convergence.
When symptoms do not change, undergo further examination with a doctor.