Pain in just one eye can come from something as minor as a scratch on the surface or as serious as a sudden spike in pressure inside the eye. The cause usually depends on what the pain feels like, whether your vision has changed, and how quickly the pain came on. Most single-eye pain resolves on its own or with simple treatment, but a few causes need urgent attention.
Surface Problems: Scratches and Foreign Bodies
The most common reason for sudden pain in one eye is a corneal abrasion, a small scratch on the clear front surface of the eye. It happens easily: a fingernail, a contact lens edge, dust, sand, or even a dried-out eye rubbed too hard. The pain is sharp and immediate, and it typically comes with the persistent feeling that something is stuck in your eye even after the object is gone. Your eye will water heavily, turn red, and become sensitive to light. You may have blurry vision on that side.
The good news is that the cornea heals fast. Minor scratches usually feel significantly better within 24 to 48 hours because the cells in that layer reproduce quickly. Larger abrasions take a few days longer but rarely cause lasting problems. Keeping your hands away from the eye, using lubricating drops, and avoiding contact lenses while it heals are the main steps. If the pain doesn’t improve within a day or two, or if something actually penetrated the eye rather than just scratching it, that warrants a closer look from a professional.
Dry Eye and Strain
Not all one-sided eye pain is dramatic. A dull, aching, or burning sensation in one eye that worsens through the day is often dry eye or eye strain, especially if you spend long hours looking at screens. You blink less when staring at a monitor, and the tear film on one eye can break down faster than the other, particularly if you sleep on one side or have slightly different tear production between eyes. The pain tends to feel gritty or tired rather than sharp, and it improves when you close your eyes or step away from what you’re doing.
Infections That Affect One Eye
Bacterial and viral infections commonly start in just one eye before spreading to the other. Conjunctivitis (pink eye) causes redness, discharge, and a gritty or burning sensation. It’s uncomfortable but not usually dangerous. A stye, an infected oil gland on the eyelid, creates a tender, swollen bump that hurts when you blink.
A more serious infection is orbital cellulitis, where bacteria spread into the tissues around the eye itself. The key signs that set this apart from a simple surface infection are pain when you move the eye, the eye pushing forward in its socket, and difficulty moving the eye in certain directions. Eyelid swelling and redness happen with milder infections too, so those alone aren’t reliable indicators. If you notice restricted eye movement along with swelling and pain, that combination needs prompt medical evaluation because the infection can progress quickly.
Inflammation Inside the Eye
Sometimes the pain comes from deeper structures. Uveitis is inflammation of the middle layer of the eye wall. It causes a deep, aching pain along with redness, light sensitivity, and blurred vision. It can develop from an autoimmune condition, a past infection, or sometimes without a clear trigger.
Scleritis, inflammation of the tough white outer coat of the eye, produces a more intense boring pain that can radiate outward to the forehead, ear, jaw, or scalp. That radiating quality is distinctive. Scleritis is often linked to autoimmune conditions and tends to need more aggressive treatment than surface-level problems.
Optic neuritis, inflammation of the nerve that connects the eye to the brain, has its own signature: over 90% of people with it experience pain that gets worse specifically when they move the eye. Vision loss usually affects the center of the visual field, creating a blurry or dark patch right where you’re trying to focus. Optic neuritis is sometimes the first sign of a condition like multiple sclerosis, so it’s taken seriously even when the vision changes are mild.
Sudden Pressure Buildup
Acute angle-closure glaucoma is one of the true emergencies that can cause severe one-sided eye pain. It happens when the drainage system inside the eye suddenly gets blocked, causing pressure to spike dramatically. Normal eye pressure ranges from about 10 to 21 mmHg. During an acute attack, pressure can surge to 60 or even 80 mmHg.
The symptoms are hard to miss. The pain is intense and comes on fast, often with a headache on the same side. You may see rainbow-colored halos around lights. Nausea and vomiting are common, which sometimes leads people to think they have a stomach problem rather than an eye problem. On examination, the pupil on the affected side is typically fixed and dilated, meaning it doesn’t react to light normally, and the eye looks red with a hazy or cloudy cornea. This needs emergency treatment to bring the pressure down and prevent permanent vision loss.
Headaches That Center on One Eye
Cluster headaches are one of the most painful headache types, and they concentrate around or behind one eye. Each attack lasts between 15 minutes and 3 hours and tends to happen daily or near-daily for weeks or months at a stretch, then disappear for a while. The pain is piercing and one-sided, and the eye on the affected side tears up, turns red, and the eyelid may droop. The nostril on that same side often gets stuffy or runny. The face can flush and sweat heavily.
Migraines can also cause pain behind one eye, though they usually come with additional features like throbbing that worsens with movement, sensitivity to light and sound, and sometimes an aura (visual disturbances like zigzag lines or flashing lights before the headache starts). If your one-eye pain keeps recurring in a pattern, especially with these companion symptoms, it’s likely headache-driven rather than an eye problem.
Sinus Pressure Referred to the Eye
Your sinuses sit directly behind and below your eyes. When the sinuses behind the cheekbones or between the eyes become inflamed or infected, the pressure and swelling can push pain into the eye area on the affected side. This type of pain tends to feel deep and achy, worsens when you bend forward, and comes alongside nasal congestion, facial pressure, or a runny nose. It improves as the sinus issue clears up.
Signs That Need Urgent Attention
Most one-eye pain is temporary and treatable, but certain combinations of symptoms signal something more serious. Seek immediate care if your eye pain comes with any of the following:
- Sudden vision loss, whether partial or complete, in the affected eye
- Rainbow halos around lights with severe pain and nausea, which suggests acute glaucoma
- A visible wound or blood leaking from the eye after an injury
- A pupil that looks different from the other side, either larger, smaller, or not reacting to light
- Restricted eye movement with swelling and pain, which may indicate orbital cellulitis
- Chemical exposure, including fumes, which requires immediate flushing and evaluation
For pain that’s mild to moderate, doesn’t involve vision changes, and started without a traumatic event, it’s reasonable to monitor for a day or two. If it persists, worsens, or starts affecting how well you see, getting an exam will help pin down the cause and rule out anything that could progress.