Definition and Overview
Diplopia is an eye disorder that causes a person to have double vision. A person with diplopia sees two images of a single object. The way a person experiences double vision may vary. Sometimes, they may see one image on top of another. In other cases, the two images are seen side by side.
Diplopia can affect one or both eyes. If it affects only one eye, it is called monocular diplopia. If it affects both eyes, it is called binocular diplopia. Of these two, the latter is more common. Studies show that it accounts for up to 89% of all cases. The former, on the other hand, only accounts for 11% of cases.
In an attempt to normalise vision, the brain sometimes suppresses or ignores signals from one eye. This can make the symptoms go away even without treatment. However, more serious cases can put the patient’s health at risk. This can happen if diplopia is caused by an underlying problem. When left untreated, this can lead to permanent vision loss in the suppressed eye. Thus, it is best to consult an eye specialist if double vision occurs. This is advised regardless if the condition is temporary or chronic.
Causes of Condition
Binocular diplopia is often caused by problems with muscles and nerves that control eye movement. The two eyes work together to enable vision. Each creates its individual image of an object. The brain then combines these two images so that the person can see them as one picture. If the muscles or nerves that control the movement of the eyes do not function properly, the brain cannot put the two images together. This causes double vision to develop.
The said muscles and nerves can be damaged or weakened. The most common cause is an underlying illness. Medical conditions that can cause diplopia include:
Graves disease - This disease affects the thyroid gland in the neck. Abnormal changes in thyroid function can sometimes affect the muscles that control the eyes.
Aneurysm or tumour - Any abnormal growth near the eyes may press on optic nerves. This may disrupt proper eye movement.
Stroke - Reduced blood supply to the blood vessels in the eyes can also cause double vision.
Diabetes - Diabetes can also affect the eye’s blood supply.
Myasthenia gravis - A medical condition that weakens the muscles.
Multiple sclerosis - A medical condition that affects the central nervous system, which includes the nerves that control the eyes.
Monocular diplopia, on the other hand, may occur due to problems within the eye. It is often associated with the following eye disorders:
Childhood squinting - Also called strabismus, this is an eye condition wherein the eyes are not properly aligned. This causes each eye to look in a slightly different direction. In patients who are being treated for this condition, their brain tries to correct their vision by suppressing signals from one of the eyes. As a side effect, they may experience double vision. This is why patients who were treated for squint in childhood have an increased risk of having double vision later in life.
Astigmatism - Patients with astigmatism are more likely to develop diplopia. This is an eye disorder in which the shape of the cornea is abnormal. It causes a refractive error that affects vision.
Other possible causes include macular degeneration and cataracts. The condition can also develop due to corneal disease and lesions in the iris.
Some people may also experience double vision temporarily. This can be caused by injuries to the head (like concussions) or trauma to the eyes (such as those that cause a black eye). Other possible causes are excessive alcohol consumption and use of certain medications. These include recreational drugs and those used for the treatment of seizures and epilepsy. Excessive strain on the eyes can also cause temporary double vision.
A person with diplopia sees double images of any object. This can cause difficulty in reading and walking. Patients also often have balance and movement problems.
Children with diplopia may also show other symptoms. These include narrowing their eyes to focus on an object or covering one eye with a hand. They may also look from the side of the eye.
Who to See and Types of Treatments Available
Patients with any of the above symptoms should see an eye specialist. Eye disorders are typically treated by ophthalmologists. These doctors are trained to diagnose and treat eye disorders as well as perform eye surgery.
Diplopia can be challenging to diagnose. This is because it can be caused by either minor or serious issues. Examples are astigmatism, nerve disease, and tumours.
The first thing that specialists do to distinguish between these two potential causes is to determine whether the condition is monocular or binocular. The former is often caused by a problem within the eye. The latter, on the other hand, is often caused by muscle or nerve issues, which are more serious.
The treatment for diplopia depends on its underlying cause. Patients with astigmatism or cataracts may undergo surgery to correct their vision problems. If the double vision is caused by these problems, the symptoms will disappear after the surgery.
However, if the disorder is caused by an underlying health problem, the patient should undergo treatment for that problem first. Treating the underlying cause will also resolve the symptoms of diplopia.
There are also some treatments that can help a patient manage his or her symptoms while waiting for or undergoing treatment. These include wearing corrective eyeglasses and performing eye exercises. Wearing opaque contact lenses and covering one eye with a patch may also help. Some are advised to get Botox injections that can help make the affected eye muscles more relaxed.
Brady CJ. “Diplopia.” MSD Manual. http://www.msdmanuals.com/professional/eye-disorders/symptoms-of-ophthalmologic-disorders/diplopia
Alves M, Miranda A, Narciso MR, Mieiro L, Fonseca T. “Diplopia: A Diagnostic Challenge with Common and Rare Etiologies.” Am J Case Rep. 2015; 16:220-223. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4410729/