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What causes double vision (diplopia)?

football player falling on his head with possible head injury and cause of diplopia (double vision)

The possible causes of double vision (diplopia) vary widely. The cause may be temporary (e.g., alcohol consumption), treatable (e.g., astigmatism) or an indicator of a more serious underlying problem (e.g., diabetes).

The medical name for double vision is diplopia. By definition, double vision makes it look like there are two of everything. This can lead to other symptoms, including headaches, nausea and vomiting.

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Eye conditions

When the physical structure of the eye is causing double vision, the cornea or the lens is usually at fault.

The cornea is the clear, front surface of the eye. All the light we see passes through the cornea before it enters the eye. A corneal problem can cause double vision in one eye or both.

Cornea conditions that can cause double vision include:

  • Astigmatism, an abnormality of the cornea’s shape. It can be present in one or both eyes, and to a different degree in each eye. About one in every three people has some level of astigmatism, according to the American Academy of Ophthalmology (AAO).

  • Keratoconus, resulting in the cornea gradually becoming more pointed and cone-shaped.

  • Dry eye syndrome, which reduces the tears and oils that coat each eye. Poor moisture or lubrication can affect the way light enters your eyes.

  • Eye infections

  • Cornea scars

After light passes the cornea and enters through the pupil, it moves through the lens. The lens is naturally clear, but cataracts cause it to become cloudy over time.

The lens plays an important role in how our eyes focus on objects. When cataracts change the lens’s appearance, you might experience double vision. The sensation usually goes away after cataract surgery.

SEE RELATED: What causes sudden double vision?

Conditions that affect the eye muscles and nerves

Double vision can occur when the muscles that control eye movement aren’t functioning properly.

Most often, the muscles attached to one eye will get weaker than the muscles of the other eye. This prevents the eyes from working together as well, leading to double vision.

These conditions include:

  • Strabismus, a condition that causes one eye to point in a different direction while the other correctly focuses on the object in front of it. The disorder can be referred to as “crossed eyes,” although the name isn’t entirely accurate. The misaligned eye can point inward, outward, upward or downward.

  • Graves’ disease, a form of thyroid eye disease. Double vision can occur due to elevated thyroid hormones (hyperthyroidism), along with eye-related symptoms like dryness, irritation, bulging and misalignment.

Since the nerves tell the muscles when to move, a problem with the nervous system can also affect the eyes. Double vision can occur when the cranial nerves send the wrong signals to one or both eyes.

Nerve-related conditions include:

  • Diabetes, a disease caused by problems with how the body controls blood sugar levels. When blood glucose levels get too high, nerve damage can lead to eye movement and other diabetic eye problems.

  • Multiple sclerosis, a disease that affects the central nervous system, can cause double vision. Not everyone who has multiple sclerosis will experience eye problems.

  • Myasthenia gravis, an autoimmune disease that changes the way the nerves talk to the muscles. In addition to double vision, ocular symptoms (ocular myasthenia gravis) can include drooping eyelids and easily fatigued eyes.

  • Guillain-Barre Syndrome, a nervous system disease that causes progressive weakness over time.

Conditions relating to the brain

Short- and long-term issues affecting the brain can cause double vision.

While double vision isn’t always a sign of something serious, it can be a medical emergency. If you’ve experienced head trauma, think you may be having a stroke or aneurysm, or have flu-like symptoms in addition to double vision, seek medical help immediately.

Brain-related issues include:

  • Migraine headaches, while painful and debilitating, are usually benign. Double vision may occur with an ocular migraine, which doesn’t cause a headache and usually lasts around 30 minutes or less. In some cases, sufferers will temporarily lose part or all of their vision.

  • Stroke, when blood has a difficult time reaching part of the brain.

  • Aneurysms, when a weak blood vessel swells up in one area, possibly leading to a rupture.

  • Brain tumors, both malignant and benign, can cause double vision, depending which parts of the brain are affected.

  • Infections like meningitis.

  • Head trauma, including concussions or eye injuries.

Other causes of double vision

Double vision isn’t always caused by an underlying medical condition. Common examples include:

  • Medications can cause double vision as a side effect or reaction. These include some forms of steroids, benzodiazepines and opiates, along with certain medications used to control cholesterol, arthritis, seizures and ulcers. For more information about a certain drug, check with your pharmacist.

  • Alcohol consumption, caused by alcohol’s slowing effect on the nerves and brain.

Don’t ignore double vision

If you experience double vision and aren’t sure what is causing it, see a doctor. Diagnosing any underlying cause of double vision, whether mild or more serious, is the first step toward treating the symptom as well as the condition.

READ MORE: Treatment for double vision

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