Double vision is seeing two, often overlapping, images of a single object. The images may be separated horizontally, vertically, or obliquely (diagonally) from each other. The medical term for double vision is diplopia.
There are two types of double vision: monocular and binocular.
Monocular diplopia is double vision in only one eye. The double vision persists even when the other eye is covered. The double does not go away when you look in different directions. Monocular diplopia can be caused by:
Astigmatism — An oval rather than spherical shape of the cornea.
Keratoconus — A cone-shaped thinning of the cornea
Pterygium — Thickening of the conjunctiva, the most superficial layer or “skin” over the whites of the eyes.
Cataracts — Clouding of the lens in the eye, a part of the natural aging process.
A dislocated lens — The lens moves out of place inside the eye or jiggles.
A mass or swelling in the eyelid — May cause pressure, or a mechanical change, on the front of the eye.
Dry eye — The cornea is not well lubricated, leading to an irregular optical surface.
Some retinal problems — When the surface of the retina is not perfectly smooth and causes image distortion.
Binocular diplopia is double vision related to a misalignment of the eyes. The double vision goes away if either eye is covered. Any problem that affects one or more of the muscles around the eyeball that control the direction of the gaze can cause binocular diplopia. These are called extraocular muscles. Such problems include:
Strabismus — A misalignment of the eyes that affects 4% of children < age 6, but can also develop in adults.
Damage to nerves controlling the extraocular muscles — Nerves can be injured by brain damage caused by infection, multiple sclerosis, stroke, head trauma or a brain tumor, especially a tumor located at the lower back portion of the brain. A tumor growing inside the eye socket or trauma to the eye socket can damage a nerve anywhere along its route to the eye muscles.
Diabetes — May lead to problems with the nerves that control eye muscle movements. Sometimes this can happen before the person is aware that he or she has diabetes.
Myasthenia gravis — A neuromuscular illness that causes the body’s muscles to tire easily and become weak. This is an autoimmune disease in which the body’s immune system mistakenly attacks the connection between the nerve and the muscles, preventing the chemical signal from getting through.
Graves’ disease — This is the most common cause of an overactive thyroid (hyperthyroidism). Some people with Graves’ disease develop double vision due to swelling and thickening of the muscles that move the eyes within the eye socket.
Trauma to the eye muscles — The muscles of the eye socket can be injured by facial trauma, especially by a fracture of the thin bones of the eye socket.
The first step is to determine whether your double vision is monocular or binocular. If you have monocular diplopia, Dr. Banik will evaluate you for conditions such as astigmatism, dry eye, or cataracts, which could be causing the problem. If the problem is binocular and there has been no facial trauma, then Dr. Banik will want to know if you have diabetes, thyroid issues, or a neurologic disorder.
For example, if Dr. Banik suspects that you have hyperthyroidism, then you will need blood tests to measure thyroid hormone levels. If she suspects that something is affecting the nerves to your eye muscles, you may need a magnetic resonance imaging (MRI) or computed tomography (CT) scan of your head to check for signs of trauma, bleeding, tumor or blood vessel malformations in the brain.
Treating double vision depends on its cause. For example, people with astigmatism that causes double vision can wear special contact lenses. Sometimes, simply updating your prescription eyeglasses takes care of the problem. Prism glasses also may be used to optically correct double vision by optically moving the image in one eye to coincide with the image in the other eye. Occasionally, as with myasthenia gravis, medications may be necessary to reduce and eliminate double vision.
Surgery is used to treat cataracts and pterygium. Strabismus surgery on the eye muscles can treat certain types of double vision. Injections of botulinum toxin (Botox) can also be used to weaken a strong eye muscle opposite the weakened one to help balance vision.
The outlook for double vision depends on its cause. For example, surgery improves the vision of more than 90% of patients with cataracts.
For most children with strabismus, the prognosis is excellent if the condition is detected and treated early.
There are many causes of double vision. It is important to get a thorough eye exam to identify the cause of the double vsion. Dr. Banik’s typical evaluation for double vision includes:
- how the eyes muscles move in different directions (motility)
- how the eyes work together (depth perception)
- alignment of the eyes
- exam under the slit lamp microscope
- dilated exam