When a person sees two images of a single object, they are most likely dealing with diplopia, a.k.a. double vision. In this article, we'll break down what diplopia is, what causes double vision, and how to diagnose or treat it.
What is Diplopia?
Diplopia (double vision) is best described as seeing two images where there should be only one. Images may overlap, appear side to side, or one may be above the other.
By default, both eyes should work together, sending the brain two images that overlap and fuse into one. When something disrupts the process, the brain receives two different signals.
Double vision can be a temporary inconvenience or a sign of something more serious. Depending on the cause, diplopia can either go away on its own or need treatment.
Why Does Diplopia Happen?
Normally, both eyes aim at the same target and send two separate images to the brain. The brain processes these images into a single, clear picture. If the eye muscles, nerves, or the brain interfere with this process, the person gets double vision.
Is Diplopia Hereditary?
Most cases of diplopia in adults are a result of nerve damage, cataracts, or strokes, so they are not hereditary. They stem from lifestyle factors, age, or underlying health issues. However, conditions like strabismus can run in families. In this case, genetics may play a role in the eye misalignment.
Diplopia is often a symptom of another condition, rather than a disease you’re born with. People can be born with disorders causing diplopia. So children with strabismus or eye muscle problems might experience double vision from a young age. Diplopia can also develop later in life due to trauma, illness, or the aging process.
RELATED: Hereditary Eye Conditions
Types of Diplopia
Seeing double can affect one eye (monocular diplopia) or both eyes (binocular diplopia).
Monocular Diplopia is when double vision persists even when one eye is closed, it often suggests an issue with the eye.
Binocular Diplopia is when double vision happens only when both eyes are open, indicating a problem with how the eyes work together. Often caused by a misalignment of the eyes.
Horizontal Binocular Diplopia is when a person sees two images side by side.
Oblique Binocular Diplopia is when the two images are displaced diagonally, it can be a combination of vertical and/or horizontal misalignments.
Vertical Binocular Diplopia is when a person sees two images of a single object stacked vertically (one image above the other).
Physiological Diplopia involves both eyes and is a normal occurrence, not due to eye misalignment or dysfunction, but a result of how the brain processes images outside the focus area. For example, when you focus on a nearby object, objects in the distance may appear doubled. The physiological type of double vision helps maintain depth perception in three-dimensional space.
Symptoms of Double Vision
The most obvious sign of diplopia is seeing two images instead of one.
Other common signs that might accompany the condition are:
Eye strain
Headache
Nausea
Dizziness
Trouble with depth perception
Squinting
Double vision can make your eyes feel tired or uncomfortable. Due to the eye strain caused by trying to focus, people with diplopia may also have headaches.
Seeing double can also make it hard to orient yourself, causing nausea or unsteadiness. It can be challenging to judge distances accurately. Some people squint to try to reduce double vision.
Who is the Risk Group for Diplopia?
While diplopia can happen to anyone, some people are more at risk due to pre-existing medical conditions or lifestyle factors.
Children: Diplopia can affect children with strabismus. If left untreated, it can result in a "lazy eye."
Adults over 50: Older adults are more prone to cataracts, strokes, and nerve damage, all of which can cause double vision.
Diabetes: Diabetes can damage the blood vessels and nerves in control of eye movements.
Thyroid diseases: Conditions like Graves’ disease increase the risk of diplopia due to muscle swelling.
Neurological conditions: People with chronic and autoimmune diseases like multiple sclerosis or myasthenia gravis are at higher risk.
RELATED: Eye Health and Chronic Diseases
Common Causes and Triggers of Diplopia
The causes of diplopia can be categorized by the part of the eye or brain it affects.
The probable causes of double vision are:
External Causes of Double Vision
Certain medications that affect the nervous system and the side effects of some drugs can temporarily make you see double. The negative effects of alcohol consumption can cause short-term double vision as well. Overexaustion and sleep deprivation may have similar effects on the human body. In addition, any trauma or injury to the eye, orbit (eye socket), or brain can affect the proper alignment or function of the eyes.
Eye Muscle Problems
The eyes cannot align properly if the muscles controlling eye movements are weak or damaged. Strabismus, or crossed eyes, is a common example. Eye muscle problems are more frequent in children but can affect adults too. Especially if they didn't get treatment during childhood.
Corneal & Lens Problems
If double vision happens in only one eye, the problem might lie with the eye lens or the cornea. Cataracts, astigmatism, keratoconus, and some corneal irregularities can cause the light entering the eye to scatter. Thus resulting in two separate images from one eye.
Neurological Conditions & Cranial Nerve Problems
The brain controls eye muscles through cranial nerves. If any of these nerves are damaged—whether by trauma, illness, or other causes—it can result in double vision. Conditions like multiple sclerosis, cranial nerve palsy, or diabetic neuropathy can damage the nerves and trigger diplopia. People with diabetes and high blood pressure are at higher risk of nerve damage.
Brain Issues
The brain processes the images from both eyes. If the problem is in the brain it may fail to fuse the images from both eyes correctly, resulting in diplopia. Some relevant double vision triggers are stroke, tumor, or head injury. Brain aneurysms and migraines are other probable causes.
Thyroid Conditions
Graves’ disease (thyroid condition) may cause the muscles around the eyes to swell, explaining the onset of diplopia.
For a more extensive list and information about each potential diplopia cause, check out our featured article below.
How to Diagnose Diplopia?
If you're seeing double, go see an ophthalmologist, as soon as possible. The eye doctor will start by taking a full medical history and asking about your symptoms. Then, they will conduct a series of tests to pinpoint the cause of your diplopia.
Steps to diagnosing diplopia and accompanying health problems:
Physical Exam
Refraction Test
Neurological Exam
Imaging Tests
Blood Tests
The doctor will examine the eyes for alignment issues and muscle function. They may ask you to track an object with your eyes or cover one eye to see if your double vision improves. Then, a refraction test will determine if astigmatism or nearsightedness is causing your diplopia.
If the problem seems nerve-related, your ophthalmologist may perform tests to assess your eye reflexes, movement, and coordination. This rules out severe neurological conditions like multiple sclerosis or myasthenia gravis.
Sometimes, an MRI or CT scan might be necessary. These imaging tests look for a possible brain tumor, aneurysm, or stroke. If brain problems are ruled out, blood tests may identify if diabetes or thyroid disease contributes to seeing double.
Double Vision Treatment
The treatment for diplopia depends on its cause. This is a breakdown of the double-vision treatment options:
Glasses or Contact Lenses
If your double vision is due to a refractive error, prescription glasses or lenses can correct the diplopia.
Prism Lenses
In some cases, special lenses (prisms( can be added to your glasses to align the two images into one. Prism lenses bend light, so the brain only receives one image, reducing or even removing double vision.
Surgery
If the cause of your diplopia is muscle-related, surgery may be necessary (in severe cases) to realign the eyes.
Treating the Underlying Medical Problem
When diabetes, a thyroid disorder, or a neurological disease causes you to see double, treating the condition may resolve the issue.
Botulinum Toxin Injections
In rare cases, Botox injections into the eye muscles may shortly paralyze them and improve alignment. The procedure is an option for strabismus or nerve-related double vision and should ONLY be performed by an ophthalmologist.
Patching
If treatment is not possible or effective, wearing an eye patch over one eye may prevent double vision by forcing the brain to ignore the input from the other eye. This is a common treatment for children.
In conclusion...
Diplopia, or double vision, can affect anyone at any life stage. The causes vary from intoxication, eye muscle problems, and nerve damage to serious brain conditions. Double vision can be a minor inconvenience, but please seek medical attention if it persists, as it may suggest another health issue.
Fortunately, many cases of diplopia are treatable through glasses, surgery, or treating the underlying problem. If you or your child experiences double vision, see an eye doctor for a diagnosis and treatment plan.
Resources:
Diplopia (Double Vision), Yale Medicine
Diplopia (Double Vision), Cleveland Clinic
Double vision, National Health Service (UK)
✅ Medically reviewed
Checked by Atanas Bogoev, MD.