Diplopia is the medical term used for seeing double image of an object. It may cause blurred vision, but the blurred vision is not due to loss of vision or blindness; it is due to diplopia.  

How does diplopia happen?

Eyes capture an image in individual fashion, i.e., acting like two cameras; each eye captures its own image, and transmits it to the brain. Light passes through the pupils to the back of the eye globe on the retina.  Retina can be compared to the old-fashioned camera film but in reality it works somewhat similar to a digital camera. Electrochemical signals triggered by different wavelength of light create a pattern of an image. These signals travel to the back of the brain for analysis. The system is so intricate and precise that both images are perceived as one. Any kind of misalignment in eyes may result in perception of two images.

 

What is the first question to ask in a patient with diplopia?

The first issue to resolve in every patient complaining of diplopia is whether it is from a problem within the eye or outside of an eye. If it is caused by a problem within an eye, such as cataract, or retinopathy, it is noted even if one eye is closed. This is called monocular diplopia. The patient is asked to close one eye at a time and see if diplopia persists with closing one or the other eye; if it does, it is a problem within the eye that is open. In this case, patient is referred to an ophthalmologist. 

If on the other hand, diplopia is only noted when both eyes are open, and it disappears when one eye is closed, it is called binocular diplopia, and the patient needs to consult a neurologist. Monocular diplopia is addressed in ophthalmology office, and is not discussed any further here.

 

What are different causes of binocular diplopia?

Eye is a small round globe like structure suspended, not rested, in the eye-socket. It is suspended by set of vertical and horizontal muscles, like tight ropes. These muscles are paired, with an opposite in the other eye-socket. Held tight by these muscles, eyes move in a yoked fashion. If a muscle is little weak, the eye it is attached to is not able to synchronize movement with the other eye, and lags behind. This disturbs the synchrony of image formation, and instead of one image, the patient sees two images. Following are some common reasons:

A: Brain aneurysm: If double vision started with a sudden severe headache (usually the worse headache of life), an emergency evaluation for aneurysm is required.

B: Ischemic stroke (stroke from blockage of a blood vessel): Headache may not be the issue, but patient may also have dizziness, unsteadiness, numbness, weakness, or difficulty speaking. If acute, emergency room evaluation for stroke is required.

C: Hemorrhagic stroke: Presentation may be similar to the ischemic stroke.

D: Neuropathy: One of the nerves controlling the eye muscles may be affected, leading to a weak muscle, and double vision. One of the common causes is diabetes mellitus. It is not an emergency as above, but still requires careful examination to make sure one is not dealing with a stroke or an aneurysm.

E: Myasthenia Gravis: This is a neuromuscular disorder (for detail, read a separate post). In this condition, the double vision can be intermittent. Patient may also have other features of this disease, such as generalized weakness, droopiness of eyelids, and speech or swallowing difficulty.

F: Grave’s disease: Due to eye muscle weakness.

G: Strabismus: Due to misalignment of eyes.

H: Multiple sclerosis: Presentation may be similar to stroke, but may not be sudden in nature.

I: High pressure in the brain: Due to Idiopathic Intracranial Hypertension.

J: Brain tumor, or a brain abscess.

K: Migraine.

 

How is the cause of diplopia diagnosed?

In most cases, urgent evaluation is needed to make sure it is not from a condition requiring emergency measures, such as an aneurysm or a stroke. Generally speaking, the cause of diplopia is diagnosed by the pattern of symptoms and the findings on examination. Investigations or tests are ordered based upon clinical presentation.

 

How is the diplopia treated?

Treatment depends upon the cause of diplopia. In many situations, diplopia is temporary, and diplopia resolves in weeks to months. If it does not, ophthalmological measures can help. In intractable cases, patching one eye is a solution.

 

Where can I get more information about diplopia?

American Academy of Neurology

American Ophthalmology Association