Double vision, or diplopia, is a symptom to take seriously. Some causes of diplopia are relatively minor, but others need urgent medical attention. WebMD takes a look at the causes, symptoms, and treatments for double vision.
What Causes Double Vision?
Opening your eyes and seeing a single, clear image is something you probably take for granted. But 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. It makes sense to consider the causes of diplopia according to the part of the visual system that has the problem. Double vision is not normal and should be reported promptly.
Cornea problems. Problems with the cornea often cause double vision in one eye only. Covering the affected eye makes the double vision go away. The abnormal surface of the eye distorts incoming light, causing double vision. Damage can happen in several ways:
- Infections of the cornea, such as herpes zoster, or shingles, can distort the cornea.
- Corneal scars can alter the cornea, creating unequal visual images.
- Dryness of the cornea can create double vision.
Lens problems. 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.
Muscle problems. 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:
- 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.
Nerve problems. 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.
- Uncontrolled diabetes can lead to nerve damage in one of the eyes, causing eye weakness and double vision.
Brain problems. 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