Double vision (diplopia) means seeing two images of one object. The NHS says it is not usually serious, but it should always be checked, even if it comes and goes.
The quickest clue is a simple test. Cover one eye, then the other. If the double image disappears when either eye is covered, both eyes are involved (binocular). This usually means the eyes are not pointing in exactly the same direction. If the doubling stays in one eye, only that eye is affected (monocular). That is usually caused by a problem with the eye itself, such as dry eye, astigmatism or a cataract.
Binocular double vision in adults deserves prompt attention. It can come from the eye muscles, the nerves that move the eyes, or the brain. Sudden double vision always needs same-day advice.
Call 112 or 999 (Ireland), 999 (UK) or 911 (US), or go to an emergency department, if double vision comes with:
Get a same-day appointment (GP, GP out-of-hours or NHS 111), if:
Do not drive yourself.
The NHS says monocular double vision is the less common type. Binocular double vision is usually a symptom of a squint, where the eyes look in slightly different directions. A squint or binocular double vision that appears in adulthood can be a sign of a more serious condition. That is why it needs checking rather than waiting.
The cover test is a guide, not a diagnosis. An optometrist or doctor will repeat it properly, along with other checks.
The NHS lists four common causes of monocular double vision:
These are usually found at a routine eye test. An optometrist (optician) is often the right first stop.
Convergence insufficiency is a common binocular vision disorder. The eyes tend to drift outwards and struggle to turn inwards for reading or close work. A Cochrane review lists symptoms including eye strain, headaches, double vision and print that seems to move on the page.
This pattern often shows up as tiredness with reading, rather than double vision at a distance. In children, the review found office-based eye exercise therapy worked better than home-based exercises. In adults, the evidence is less clear. An optometrist can test for it.
Thyroid eye disease is an autoimmune condition. The muscles, eyelids, tear glands and fatty tissue around the eye become inflamed. When the muscles that move the eye swell and stiffen, the eyes can stop moving in line. The result is double vision.
The British Thyroid Foundation says about 40% of people with Graves' disease develop thyroid eye disease. In most people it is mild. Only 5–6% of people with Graves' disease develop moderate to severe eye disease. Smoking doubles the risk, and heavy smoking increases it about eightfold.
The NHS says about 4 in 5 people with an overactive thyroid have Graves' disease. We explain the thyroid blood tests in thyroid and the brain.
Myasthenia gravis is a rare long-term condition that causes muscle weakness. It most often affects the muscles of the eyes and eyelids first. Typical early signs are a drooping eyelid and double vision.
The pattern is the clue. The NHS says symptoms tend to get worse when you are tired. Many people are worse at the end of the day and better after sleep. It typically starts in women under 40 and men over 60. For some people, only the eye muscles are ever affected.
NICE lists double vision among the most common symptoms people with MS first present with. Others include loss of vision in one eye with painful eye movements, and spreading numbness or weakness.
NICE adds that people with MS are often under 50 when symptoms start. Symptoms usually develop over more than 24 hours, persist for days or weeks, and then improve. Our article on multiple sclerosis explains how it is diagnosed and managed.
Nerves control the muscles that move the eyes. If one stops working properly, the eyes go out of line. A third nerve palsy can cause a drooping eyelid, limited eye movement and a widened (dilated) pupil.
The causes range from minor to life-threatening. In a series of 633 patients at a South Korean referral hospital, the most common cause (26.5%) was "microvascular". This means damage to the nerve's small blood vessels, in adults with vascular risk factors such as high blood pressure, diabetes or smoking. By the study's definition, these cases recovered on their own within a year. Vascular anomalies, including aneurysms, were the next most common (17.4%).
A pupil that is affected matters. A 2025 review advises that an aneurysm should be ruled out first when the pupil is involved. The NHS treats double vision with a dilated pupil as a 999 emergency.
Migraine deserves a note. The NHS migraine page says to call 999 for a headache with blurred or double vision. NICE also treats double vision during a migraine aura as atypical, a reason to consider further investigation or referral.
Expect questions like these:
The NHS says an optician or GP will do some simple, painless eye tests. These usually include checking how each eye moves, how the pupils react, and the eyelids. They may refer you to a hospital eye specialist.
Further tests depend on what they find:
In the UK, the NHS says you must stop driving and tell the DVLA if you are diagnosed with double vision. You can drive again if a doctor tells the DVLA it is safe.
In Ireland, the 2026 medical fitness to drive guidelines (Sláinte agus Tiomáint) say car drivers must stop on detection. Driving can resume once the NDLS has confirmation that it is controlled. Control can be by glasses (with or without a prism) or a patch worn while driving.
In the US, ask your doctor whether it is safe for you to drive.
Tiredness can make some causes more noticeable. Convergence insufficiency often causes eye strain and double vision during long close work. Myasthenia gravis typically gets worse as the day goes on and improves after sleep. Tiredness is not a reason to ignore new double vision. Get it checked.
For double vision that comes and goes, the NHS says an optician or GP is the right first step. If it started suddenly, or you have eye pain, ask for an urgent same-day appointment. If any "Get help now" sign is present, call 112, 999 or 911.
Monocular double vision is usually caused by an eye problem such as astigmatism, dry eye or a cataract. These are rarely emergencies. It still needs an eye examination to confirm the cause.
Sometimes it does, depending on the cause. But the NHS says to get it checked even if it comes and goes. Symptoms of stroke that resolve are still an emergency, because a TIA can come before a stroke.
This article is general information, not medical advice. It cannot assess your symptoms. If you are worried, speak to your GP, optometrist or emergency services.
Reviewed by: Proco Team
Last updated: November 2026