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Binocular Diplopia

What Is It, Causes, Diagnosis, and More

Author: Corinne Tarantino, MPH

Editors: Ahaana Singh, Ian Mannarino, MD, MBA

Illustrator: Abbey Richard

Copyeditor: Joy Mapes

What is binocular diplopia?

Double vision, also called diplopia, causes an individual to see two overlapping sets of images. Binocular diplopia refers to double vision due to misalignment of the eyes, often caused by weakness or restricted movement of the muscles surrounding the eye (i.e., extraocular muscles). Binocular diplopia occurs when both eyes are open, so it can resolve when one eye is covered or closed. 

What causes binocular diplopia?

There are many potential causes of binocular diplopia, including problems with the eye muscles, neuromuscular diseases, damage to the cranial nerves, and neurological or brainstem disorders.

Graves’ ophthalmopathy, orbital myositis, and muscular entrapment can all create problems with the eye muscles. Graves' ophthalmopathy, or thyroid eye disease, is an autoimmune disorder that causes inflammation and swelling around the extraocular muscles, consequently restricting the eyes’ range of movement. Similarly, ocular myositis is an inflammatory condition that affects the extraocular muscles. Injuries can also interfere with the eye muscles. When a trauma breaks bones around the eye, a muscle can get caught in the bone fragment, potentially reducing eye mobility and leading to double vision.

Neuromuscular diseases, such as myasthenia gravis and botulism, affect neurons at the neuromuscular junction and can lead to binocular diplopia. Myasthenia gravis is a neuromuscular disease in which the body’s immune system blocks communication between nerves and muscles, causing muscle weakness and fatigue. There are two types of myasthenia: ocular and generalized. Ocular myasthenia gravis affects only the eyes, while generalized myasthenia gravis causes body-wide symptoms in addition to binocular diplopia. In the case of botulism, a bacterial toxin causes muscle weakness, particularly in the face.

Cranial nerves, which go directly from the brain to the area they innervate, are also involved in vision. Damage to cranial nerves III, IV, and VI may cause double vision. Such damage may be a result of conditions including diabetes, infection, inflammation, or a cerebral aneurysm, which happens when blood flow causes a weak spot in a brain artery to protrude. 

Double vision may also be a result of problems in the nervous system due to a neurological disorder. For example, multiple sclerosis is a neurological disorder that often causes diplopia by damaging the myelin sheaths, or protective barriers, on the nerves that facilitate vision. 

Finally, brainstem disorders, which are rare and often caused by a stroke, tumor, demyelination, or infection, can also lead to binocular diplopia. A stroke occurs when a blood vessel is blocked, preventing oxygen from getting through to part of the brain, including areas that affect the eyes. Tumors may grow in areas of the brainstem affecting the eyes. Severe central nervous system infections, such as meningitis, may also lead to swelling or inflammation around the brain stem and subsequently block the nerves from sending messages to the eyes.

How can you tell the difference between monocular and binocular diplopia?

Monocular and binocular diplopia can be differentiated from one another by covering one eye at a time. Monocular diplopia, which is when double vision affects only one eye, is pronounced when the unaffected eye is covered, and it appears to resolve when the affected eye is covered. In contrast, an individual with binocular diplopia sees double when both eyes are uncovered, and their double vision resolves when they cover either eye. Monocular double vision usually indicates a problem with a structure in one eye. Dry eye is a common cause of monocular diplopia, as reduced tear production can damage the front of the eye. Refractive error, which occurs when the shape of the eye keeps light from hitting the retina properly, is another source of monocular diplopia.

How is binocular diplopia diagnosed and treated?

Diagnosis of binocular diplopia focuses on determining the underlying cause. Diagnosis often begins with a medical examination, including a physical examination and review of symptoms and medical history. During the physical examination, a clinician will often test the individual’s sight while covering one eye at a time to differentiate between binocular and monocular diplopia. Additionally, the clinician may ask the individual to move their eyes in different directions, which can show whether a particular eye muscle or cranial nerve is affected. If only one muscle is affected, the diplopia will be worse when the individual looks in the direction of the affected eye muscle. Depending on the suspected cause, blood tests may be performed to diagnose the condition, such as testing for myasthenic antibodies in the case myasthenia gravis is suspected. Occasionally, magnetic resonance imaging (MRI) or other appropriate imaging will be performed to diagnose a condition affecting the brainstem, like a stroke.

Specific treatment varies depending on the underlying cause, but supportive measures can be taken to reduce associated symptoms. Sometimes the double vision will resolve on its own over time without any treatment. In the case that binocular double vision persists, the individual may wear an eye patch over one eye to make their vision clearer. If double vision continues for an extended period of time, eyeglasses with prism lenses, a kind of lens that can help align images, may be recommended.

Can binocular diplopia be cured?

Binocular diplopia may be cured depending on the underlying condition. Some conditions have no cure (e.g., multiple sclerosis) while others do (e.g., meningitis). 

What are the most important facts to know about binocular diplopia?

Binocular diplopia is double vision caused by a misalignment of the eyes. Binocular double vision has many causes, including problems with the eye muscles, neurological and neuromuscular disorders, damage to the cranial nerves, and brainstem disorders. Monocular and binocular diplopia may be differentiated by covering one eye. With binocular diplopia, double vision will resolve when either eye is covered, whereas monocular double vision will resolve when only the affected eye is covered. Diagnosis requires a clinical examination involving eye movement tests and, depending on the suspected cause, possibly blood tests or imaging. Treatment focuses on reducing double vision directly, such as by wearing eye patches or prism lens glasses, as well as on addressing the underlying condition. Binocular diplopia is curable only when the underlying condition can be cured.

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