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.
Cornea problems. 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. Double vision is caused by the abnormal surface of the eye distorting incoming light. Danormally. the mage 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.
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 a 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.