Pain behind one eye is almost always caused by one of a handful of conditions, ranging from everyday triggers like eye strain and sinus pressure to more intense causes like migraines and cluster headaches. The fact that it’s on the left side specifically doesn’t usually point to a different set of causes than right-sided pain, but one-sided pain does help narrow the list. Understanding what else is happening alongside the pain is the fastest way to figure out what’s going on.
Migraine With Eye Pain
Migraine is one of the most common reasons for recurring pain behind one eye. The headache phase typically lasts several hours to three days, and the pain is often felt on one side of the head, frequently centering around or behind the eye. Before the headache arrives, you may notice subtle warning signs (called prodrome) like mood changes, food cravings, or fatigue that can start hours or even days earlier. About 20% of people with migraine also experience aura, which can include visual disturbances like zigzag lines or temporary blind spots, usually lasting 5 to 60 minutes.
What sets migraine apart from other causes is the package of symptoms that travels with it: nausea, sensitivity to light and sound, and pain that worsens with physical activity. After the headache fades, many people feel drained or foggy for hours. If you’re getting these episodes repeatedly and they fit this pattern, migraine is a strong possibility.
Cluster Headaches
Cluster headaches produce some of the most severe pain you can experience, and they almost always strike on one side, locking onto the same eye each time. The pain is burning, sharp, or stabbing, centered from the neck to the temple and often boring directly into or behind the eye. It reaches full intensity within 5 to 10 minutes and stays at its worst for 30 minutes to 2 hours, though individual attacks can range from 15 minutes to 3 hours.
The telltale signs that separate cluster headaches from migraine are the accompanying symptoms on the same side as the pain: a watery or red eye, a drooping eyelid, a constricted pupil, a runny or stuffy nostril, and facial flushing with heavy sweating. These attacks tend to strike at the same time each day, often 2 to 3 hours after falling asleep, and they come in “clusters” that last weeks or months before disappearing for at least a month. Some people have chronic cluster headaches that persist for a year or longer without a break.
Sinus Pressure and Infection
Your sinuses sit in several places around your eyes and nose, and when they’re inflamed or infected, the pain can radiate directly behind the eye. The sphenoid sinus, which sits deep in the center of the skull, is particularly notorious for this. A sphenoid sinus infection creates a deep, dull ache that feels like it’s coming from the very center of your head or behind both eyes, and it typically gets worse when you lie down or bend forward.
This type of sinus pain is often accompanied by thick nasal discharge and a feeling of deep pressure. It’s commonly mistaken for a tension headache because the symptoms can seem vague, which leads many people to wait longer than they should before seeking treatment. If your pain behind the eye comes with congestion, reduced sense of smell, or a feeling of fullness in your face, sinus involvement is worth considering.
Eye Strain and Refractive Errors
Prolonged screen time can cause aches and pain behind the eyes, a condition often called digital eye strain or computer vision syndrome. This pain tends to build gradually during the day and ease when you rest your eyes. It’s typically felt in both eyes, but if you have an uncorrected or unevenly corrected refractive error (meaning one eye works harder than the other to focus), the strain can feel worse on one side. If you notice the pain is tied to long stretches of reading, computer work, or phone use, this is one of the simpler explanations to test by taking breaks and getting your prescription checked.
Optic Neuritis
Optic neuritis is inflammation of the nerve that connects the eye to the brain, and it usually affects only one eye. The hallmark symptom is a dull ache behind the eye that gets noticeably worse when you move your eyes. Vision changes often accompany the pain: blurry or dimmed vision that develops over hours to days, loss of color vividness (colors look washed out), blind spots in your central or side vision, and sometimes flashing or flickering lights when you move your eyes.
Most people recover at least some vision over several weeks to months, though vision loss is permanent in some cases. Optic neuritis can be an early sign of conditions that affect the protective coating around nerves, so it warrants prompt medical evaluation, especially if you’re experiencing vision changes alongside the pain.
Acute Angle-Closure Glaucoma
This is the one cause on this list that qualifies as a true emergency. Acute angle-closure glaucoma happens when pressure inside the eye spikes suddenly because fluid drainage gets blocked. The symptoms come on fast: severe eye pain, a visibly red eye, blurred vision, rainbow-colored halos around lights, headache, and nausea or vomiting. If you’re experiencing sudden, intense eye pain with vision changes and nausea, this needs immediate attention because permanent vision loss can happen within hours.
Vascular Causes
Less commonly, pain behind one eye can signal a problem with the blood vessels supplying the brain. A carotid artery dissection, which is a tear in the inner wall of one of the major arteries in the neck, can cause pain around the eye as its only symptom. It may also produce a drooping eyelid, a smaller pupil on one side, and reduced sweating on that side of the face (a pattern called Horner’s syndrome). This combination of eye pain with eyelid and pupil changes on the same side is a red flag that points away from more routine causes.
How Doctors Sort It Out
The single most useful tool for diagnosing pain behind the eye is a detailed description of what you’re experiencing. Doctors will want to know when the pain started, how long each episode lasts, what makes it better or worse, and what other symptoms come with it. These details matter more than you might expect. A headache lasting under 4 hours points toward a different category than one lasting 4 to 72 hours. Pain that peaks within seconds raises different concerns than pain that builds over minutes.
Pay attention to the associated symptoms. Nausea and light sensitivity suggest migraine. A red, teary eye with a stuffy nose on the same side points toward cluster headache. Pain that worsens with eye movement and comes with vision changes suggests optic neuritis. Deep pressure that worsens when bending forward leans toward sinus disease. The pain itself is only half the story. The company it keeps is what reveals the diagnosis.
A physical exam typically includes checking your vision, looking at the structures of your eye, assessing the nerves in your face, and sometimes feeling the arteries in your temples and neck. Depending on the suspected cause, imaging or pressure measurements inside the eye may follow.