Double vision is one of the most common reasons why other doctors refer their patients to me. Patients typically identify double vision rather easily. In some cases the two images are completely separate, and in other cases, they are overlapping. Double vision might occur in specific circumstances (for example, when looking in the distance, at near, or in a particular direction). In some cases, the double vision may fluctuate throughout the day, being most prominent during periods of fatigue. Patients with some forms of double vision may find themselves closing one eye to improve their vision.
Is double vision due to a problem in the eye or in the brain?
The key to understanding whether double vision is due to a problem in the eye or in the brain is to see what happens when one eye is closed. If the double vision persists despite closing or occluding one eye (Monocular), then the cause is ophthalmological—such as dry eyes, cataract, macular problem, or another eye disease. On the other hand, when double vision is present with both eyes open but goes away when one eye is closed or occluded (Binocular), the cause is typically neurological. This type of double vision occurs because of misaligned eyes. When the eyes are not aligned properly, one eye sees an image in one location, while the other eye sees the same image in another location. Understandably, the brain becomes confused and sees two images instead of one. When one eye is closed, the double vision immediately goes away, because the brain receives information from just one eye.
One eye may look straight ahead, while the other eye turns inward, outward, upward, or downward. The eye turn may be constant, or it may come and go. Which eye is straight (and which is misaligned) may switch or alternate. Six different muscles surround each eye and work “as a team” so that both eyes can focus on the same object. When someone develops double vision, these muscles do not work together. As a result, one eye looks at one object, while the other eye turns in a different direction and is focused on another object. When this occurs, two different images are sent to the brain and cause double vision.
What causes double vision?
Double vision or diplopia can be caused by a cranial neuropathy. There are three cranial nerves that control the movement of the eyes. Third nerve raises the eyelid, makes the pupil to constrict, and allows the eye to move up, down, and in. Fourth nerve rotates the eye in and makes it to go down. Sixth nerve allows the eye to turn out. Injury (tumor, aneurysm, inflammation, or lack of blood flow) to any or combination of these cranial nerves will cause double vision.
Double vision can also occur due to skew deviation, which is vertical misalignment of the eyes that does not map out to any cranial nerve. This is thought to be caused by a pathology in midbrain. Double vision can also occur as a result of internuclear ophthalmoplegia due to interruption of information traveling between the third and sixth nerve in brainstem. In young patients, this is almost always caused by multiple sclerosis. In aged population, this is typically caused by a tiny stroke in midbrain/brainstem. Temporal arteritis, which is an autoimmune inflammation of arteries, affecting exclusively older population, can cause double vision by vascular injury to the nerve or the eye muscles. Lyme disease can cause cranial neuropathy, most commonly seventh or facial nerve palsy, but it can also cause third, fourth, or sixth nerve palsy to produce diplopia.
Double vision can occur with orbital process as well. Thyroid eye disease and idiopathic orbital inflammation can both affect the eye muscles to cause double vision. Orbital tumor can cause double vision by mass effect. Orbital infection, which is usually spread from severe sinus infection, can also cause double vision. Orbital fracture from trauma can cause double vision as well. Certain types of mitochondral disorder can cause chronic progressive external ophthalmoplegia, which causes the eye movement to diminish over time. This can cause double vision as well. Neuromuscular disorder, such as myasthenia gravis, interrupts the information traveling from the nerve ending to the muscle and cause double vision.
Finally, decompensating congenital strabismus (lazy eye) can cause double vision. As stated above, the differential diagnoses for diplopia is quite broad. One of the most common causes of double vision is microvascular cranial neuropathy, usually seen in people with long standing diabetes or hypertension. In this instance, double vision occurs as a result of third, fourth, or sixth nerve palsy from lack of blood flow to the nerve as a result of small vessel disease caused by diabetes or hypertension. Fortunately, in these situations, double vision commonly (but not always) improves or goes away altogether over ensuing 3 months from the onset. Besides the suspected microvascular etiology causing double vision, almost all patients with double vision will need to go through a thorough work up, including imaging studies, such as MRI, MRA, CT, CTA, and/or angiogram,
and blood tests. Unfortunately, even after a thorough work up, many times the exact cause of double vision is not found, which can be very frustrating to the patient as well as to the doctor. Even in these cases, treatment may be available.
What treatments are there for double vision?
After the causes of double vision are investigated, your doctor might be able to predict approximately how long the double vision may last. Some cases recover on their own, whereas in other cases, the double vision can persist. In some cases, the treatment is targeted at the cause of double vision. For example, some conditions will require oral medication, such as steroids for certain inflammatory conditions causing ouble vision, antibiotics for lyme disease, and mestinon and other medications used for myasthenia gravis. For most people, even in cases where the specific cause is not found, the treatment is focused on lessening the symptom of double vision.
One approach is to block vision from one eye. This can be done either by using an eye patch or by using scotch or electric tape to cover one lens of the eyeglasses. Depending on the exact pattern of the ocular misalignment, temporary prism can sometimes be tried to reduce the double vision. If these are very effective, permanent prism can be ground into the lenses of the eyeglasses. Prism basically bends the light to simulate misaligned eyes as if they are aligned properly. Finally, when the ocular misalignment has become permanent and stable without any change over 6-12 months, eye muscle surgery may be an option to realign the eyes.