What is Double Vision?
Double vision, or diplopia, is a symptom to take seriously. Some causes of diplopia are relatively minor, but others need urgent medical attention.
What Causes Double Vision?
Opening your eyes and seeing a single, clear image might be something you take for granted. That seemingly automatic process depends on the orchestration of multiple areas of the vision system. They all need to work together seamlessly:
- The cornea is the clear window into the eye. It does most of the focusing of incoming light.
- The lens is behind the pupil. It also helps focus light onto the retina.
- Muscles of the eye -- extraocular muscles -- rotate the eye.
- Nerves carry visual information from the eyes to the brain.
- The brain is where several areas process visual information from the eyes.
Problems with any part of the vision system can lead to double vision.
Problems with the cornea often cause double vision in one eye only. Covering the affected eye makes the double vision go away. If the cornea has a symmetrical shape, glasses may correct the double vision from one eye. The double vision is caused by the abnormal surface of the eye distorting incoming light. This can happen in several ways:
- Keratoconus is the most common cause of double vision in an individual eye that is not corrected with glasses.
- Infections of the cornea, such as herpes zoster (shingles) or herpes simplex can distort the cornea.
- Corneal scars can alter the cornea, creating unequal visual images.
- Dryness of the cornea can create double vision.
Cataracts are the most common problem with the lens that causes double vision. If cataracts are present in both eyes, images from both eyes will be distorted. Cataracts are often correctable with minor surgery.
If a muscle in one eye is weak, that eye can't move smoothly with the healthy eye. Gazing in directions controlled by the weak muscle causes double vision. Muscle problems can result from several causes:
- The neurological system that keeps muscles in sync may not be functioning
- Myasthenia gravis is an autoimmune illness that blocks the stimulation of muscles by nerves inside the head. The earliest signs are often double vision and drooping eyelids, or ptosis.
- Graves' disease is a thyroid condition that affects the muscles of the eyes. Graves' disease commonly causes vertical diplopia. With vertical diplopia, one image is on top of the other.
Several different conditions can damage the nerves that control eye muscles and lead to double vision:
- Multiple sclerosis can affect nerves anywhere in the brain or spinal cord. If the nerves controlling the eyes are damaged, double vision can result.
- Guillain-Barre syndrome is a nerve condition that causes progressive weakness. Sometimes, the first symptoms occur in the eyes and cause double vision.
- Diabetes can lead to nerve damage affecting the muscles which move the eyes, causing double vision.
The nerves controlling the eyes connect directly to the brain. Further visual processing takes place inside the brain. Many different causes for double vision originate in the brain. They include:
- Increased pressure inside the brain from trauma, bleeding, or infection
- Brain tumors
- Migraine headaches
What Are the Symptoms of Double Vision?Double vision can occur by itself with no other symptoms. Depending on the cause, other symptoms may be present with double vision, such as:
- Misalignment of one or both eyes (a "wandering eye" or "cross-eyed" appearance)
- Pain with eye movements in one or both eyes
- Pain around the eyes, such as in the temples or eyebrows
- Weakness in the eyes or anywhere else
- Droopy eyelids
What Are the Symptoms of Double Vision?
Double vision that's new or unexplained needs urgent medical attention. With so many potentially serious causes for double vision, it's important to discover the reason without delay.
Your doctor will most likely use multiple methods to diagnose the cause for double vision. Blood tests, a physical exam, and possibly imaging studies like computed tomography (CT) or magnetic resonance imaging (MRI) are frequently used.
One of the most effective tools in diagnosing diplopia, though, is the information you can provide. You can make the diagnosis for double vision more accurate by answering several questions beforehand.
- When did the double vision start?
- Have you hit your head, fallen, or been unconscious?
- Were you in a car accident?
- Is the double vision worse at the end of the day or when you're tired?
- Have you had any other symptoms besides double vision?
- Do you tend to tilt your head to one side? Look at old pictures, or ask family -- you may not even be aware of the habit.
Now, focus on something unmoving in your field of vision -- a window or a tree.
- Are the two objects side by side, or is one on top of the other? Or are they slightly diagonal? Which one is higher or lower?
- Are both images clear but simply unaligned with each other? Or is one image blurry and the other clear?
- Cover one eye, then uncover it and cover the other. Does covering either eye make the double vision go away?
- Pretend your field of vision is a clock face. Move your eyes around the clock, from noon to six and up to 12 again. Is your double vision worse at any clock position? Does any position make your double vision improve?
- Tilt your head to the right, then to the left. Do any of these positions improve the double vision, or make it worse?
How is Double Vision Treated?
With double vision, the most important step is to identify and treat the underlying cause. In some cases, double vision can be improved by managing or correcting its cause.
- If weak eye muscles are the cause, or if a muscle has been pinched as a result of injury, surgery may help.
- Myasthenia gravis can be treated with medications.
- Graves' disease is treatable with surgery or medical therapy.
- Blood sugar in diabetes can be controlled with medicines and/or insulin.
If double vision can't be reversed, treatments can help people live with double vision. Sometimes, this requires wearing an eye patch or special prism glasses to minimize the effect of double vision.