Diplopia: Double vision and ghost images
This article will help you understand diplopia (double vision), including causes of double vision and definitions of horizontal, vertical and monocular diplopia.
What is diplopia?
The definition of diplopia is simple: It means double vision — that is, seeing two separate or overlapping images of the same object when you should only be seeing one.
Sometimes, the term "ghost image" is used to describe the less dominant image present during diplopia.
Types of diplopia include:
- Horizontal diplopia: Double vision where the two images are separated laterally (horizontally).
- Vertical diplopia: Double vision where one image is higher than the other.
- Monocular diplopia: Double vision that persists in one eye when the other eye is closed.
Diplopia can be a symptom of very serious health problems. See a physician or an eye doctor near you immediately of you start experiencing double vision.
Temporary episodes of double vision can happen for many reasons, including drinking too much alcohol or being overly tired. This type of short-term double vision is usually not cause for worry.
But if diplopia is long-lasting or keeps coming back, causes can include:
- Stroke, head injury, brain tumor, brain swelling or brain aneurysm. A head or brain injury, tumor, stroke or related condition can cause diplopia.
- Eye problems. Eye conditions such as keratoconus, cataracts and even dry eyes can cause double vision. (Most cases of monocular diplopia are caused by eye problems.)
- Refractive surgery. If you have had LASIK, PRK, or any refractive surgery to help you see better without glasses or contacts, you may experience some minor double vision or ghost images because of changes to your corneas. An irregular corneal surface, caused by the surgery itself or by dryness, may cause light rays to scatter instead of focusing properly. Diplopia from refractive surgery usually clears up within weeks or months. But in some cases, a second laser vision correction procedure might be necessary.
- Cranial nerve palsies. Double vision also can be caused by paralysis or loss of coordination of one or more muscles that control the position and teaming of the eyes due to a cranial nerve palsy. Cranial nerve palsies can be caused by diabetes, head injury, tumor, multiple sclerosis, meningitis, high blood pressure, blockage in an artery or an aneurysm.
Diplopia and strabismus
The ability to see a single image with two eyes involves a complex system of muscles, nerves and other eye parts.
When two eyes correctly and accurately point and focus at the same time, we see only one image of the world. When two eyes point and focus differently from each other, diplopia may occur.
Some people are born with eyes that are not properly aligned — a condition called strabismus. Eyes can be crossed inward or turn outward. One eye can even go up while the other goes down.
If you have strabismus, you will see double if your brain allows it, because each eye sees a different thing at the same time. But the brain usually adapts by shutting down or ignoring the information from one eye. This is called suppression. Surgery or vision therapy can help many people with strabismus.
Generally, treatments for double vision can include surgery, vision therapy, prism in the glasses prescription or medications.
Double vision can occur when the eyes look in separate directions because of cranial nerve palsies, strabismus or other reasons.
Again, it's important to see an eye doctor immediately if you experience diplopia. Depending on its cause, your eye doctor may be able to immediately treat the double vision or will recommend a specialist (such as a neurologist or neurosurgeon).
If you have sudden double vision that you ignore and then it goes away over a long time period, this may mean your brain has tuned out one of the images (suppressed it). Although this is certainly more comfortable and bearable for you, it's not a good sign. Suppression could be masking a serious problem that needs treatment.
Some conditions causing double vision are difficult, if not impossible, to fix. Some strokes and nerve palsies cause fluctuating double vision that can't be measured accurately enough to correct.
In these cases, you may need a period of adjustment so that you can learn to live with the symptoms. Your eye doctor can help by prescribing glasses that have special prisms in the lenses to reduce the diplopia.
Other possible temporary treatments for diplopia include patching one eye for periods of time or prescribing special contact lenses.
Remember: The sudden onset of diplopia could signal a condition that may be a matter of life or death, such as a brain tumor or aneurysm. So see an eye doctor near you immediately if you experience double vision unexpectedly.
Page updated June 2019