Double vision, also called diplopia, is more common than you might think, especially as we get older. Thankfully, most causes of double vision can be treated once you find out what is behind them.
If you have ever blinked hard, rubbed your eyes and still found yourself asking, “Why am I seeing double?” you are not alone. Seeing two of something that should be one is unsettling, and it can make reading, driving and even walking down stairs feel uncertain and dangerous.
So, what causes double vision? Sometimes it is something as simple as dry eyes or an outdated prescription. Other times, it is a sign of a health condition that needs prompt attention. This guide explains the most common causes, how to tell the difference, and when to get help.
What Is Double Vision?
Your eyes each capture a slightly different image of the world. Your brain then blends those two images into one clear, three-dimensional picture.
Double vision happens when something interrupts that process. Either light is not focusing properly inside one eye, or your eyes are not lined up and working together. The result is two images of a single object, side by side, one above the other, or on an angle.
Monocular vs Binocular Double Vision
Before looking at the causes, it helps to know which type of diplopia you have. There is a quick way to check at home.
- Monocular double vision stays when you cover one eye. The problem sits within one eye itself, and it is usually the less serious type.
- Binocular double vision disappears when you cover either eye. It means your eyes are not aligned, which can be linked to muscle, nerve or brain conditions.
Knowing which type you have gives your optometrist a valuable head start, so take note before your appointment.
Common Causes of Double Vision
There are many possible causes of double vision, ranging from everyday eye problems to conditions that affect the whole body. Here are the most common ones.
Astigmatism and Uncorrected Refractive Errors
Astigmatism happens when the cornea is shaped more like a rugby ball than a soccer ball, so light does not focus evenly. This can create ghosting or a faint second image, especially with letters and lights. Short-sightedness and long-sightedness can have a similar effect when left uncorrected.
Dry Eyes
A healthy tear film keeps the surface of your eye smooth. When it breaks down, your vision can blur or double, then clear again when you blink. This is especially common with long hours on screens, air conditioning and wearing contact lenses.
Cataracts
As cataracts cloud the natural lens of the eye, light scatters instead of focusing on a single point. Many people notice double or ghosted images in one eye, along with glare and faded colours.
Keratoconus
Keratoconus is a condition where the cornea gradually thins and bulges into a cone shape. It often starts in the teens or twenties and can cause blurred, distorted or double vision in one eye.
Poorly Fitting Glasses or Contact Lenses
An old prescription, scratched lenses, frames that sit crooked or contact lenses that move around too much can all leave you seeing double. It is one of the easiest causes to fix, which is why regular eye tests matter.
Eye Alignment and Focusing Problems
Some eye problems affect how well your eyes team up rather than the eyes themselves. Strabismus (a turned eye), convergence insufficiency (difficulty keeping both eyes pointed at close objects) and binocular vision dysfunction can all lead to binocular double vision. Symptoms often get worse when you are tired or doing a lot of close work.
Health Conditions
Several conditions that affect the nerves and muscles controlling your eyes can cause double vision, including:
- Diabetes, which can damage the nerves that move the eyes.
- Thyroid eye disease, which causes swelling of the eye muscles.
- Myasthenia gravis, which weakens the muscles, often getting worse later in the day.
- Multiple sclerosis, which can affect the nerves that coordinate eye movement.
- Migraines, which can bring on temporary visual disturbances.
Head Injury, Stroke and Other Serious Causes
A knock to the head, a stroke, a brain aneurysm or a tumour can all damage the nerves or brain areas responsible for eye movement. Double vision that appears suddenly, especially alongside other symptoms, should always be treated as an emergency.
Why Am I Seeing Double Sometimes?
Double vision that appears at the end of a long day and disappears after a good night’s sleep is more common than you might think. So, why am I seeing double only some of the time? The answer often comes down to fatigue. When your eyes are tired, they find it harder to stay aligned and focused.
Double vision that comes and goes is often linked to:
- Long hours of screen time or reading.
- Lack of sleep.
- Dry eyes.
- Alcohol.
- Convergence insufficiency or other eye teaming problems.
Even if it settles on its own, intermittent double vision is worth having checked. It can be an early sign of a binocular vision issue or a health condition that is easier to manage when caught early.
When Is Double Vision a Medical Emergency?
Go to your nearest emergency department straight away if double vision:
- Comes on suddenly and does not go away within a few hours.
- Follows a head injury, fall or car accident.
- Comes with a severe headache, eye pain, dizziness or vomiting.
- Comes with weakness, numbness, a drooping face or eyelid, slurred speech or confusion.
These can be signs of a stroke or another serious condition, and every minute counts.
How Double Vision Is Diagnosed and Treated
Your optometrist will start by finding out whether your double vision is monocular or binocular. A comprehensive eye exam usually includes a vision check, a slit lamp examination of the front of the eye, and tests of how your eyes move and align. If a nerve, muscle or brain condition is suspected, you will be referred to your GP or an ophthalmologist for further tests such as an MRI or blood tests.
Treatment depends on the cause, and may include:
- New glasses or contact lenses to correct refractive errors and astigmatism.
- Prism lenses, which bend light so both eyes see a single image.
- Eye drops and dry eye treatments to restore a healthy tear film.
- Vision therapy to strengthen how your eyes focus and work together.
- Cataract surgery or specialist treatment for keratoconus.
- Managing an underlying condition such as diabetes or thyroid disease.
Get Your Double Vision Checked at Clear Vision Optical
So, what causes double vision? It could be anything from dry eyes or an old prescription to a muscle, nerve or health condition. The only way to know for sure is to have your eyes properly assessed.
At Clear Vision Optical, our optometrists check for the full range of eye problems behind double vision, including a dedicated Binocular Vision Dysfunction Test and vision therapy for eye teaming issues. We work closely with local GPs and ophthalmologists, so if you need further care, you will be in good hands.
Book your eye test online today and get back to seeing one clear picture.
