Pain in one eye usually comes from something minor and treatable, like a scratch on the surface, dryness, or a sinus flare-up. But because the eye is so sensitive and some causes need fast treatment, it helps to narrow down what’s going on based on how the pain feels, when it started, and what other symptoms came with it.
Surface Problems: Scratches and Foreign Objects
A corneal abrasion, or scratch on the clear front surface of your eye, is one of the most common reasons for sudden, sharp pain in one eye. It can happen from a fingernail, a contact lens, dust, or even rubbing your eye too hard. The pain is typically immediate, with a gritty sensation like something is stuck under your eyelid. Tearing, redness, and sensitivity to light usually follow.
Minor corneal abrasions heal quickly. Most people feel significantly better within 24 to 48 hours. Treatment often starts with flushing the eye with clean water or saline. In some cases, a provider will place a special bandage contact lens over the scratch to protect it and reduce pain from blinking. If you’re still in significant pain after a day or two, or if your vision seems affected, that’s a sign the injury may be deeper than a simple scratch.
Dry Eye That Hits One Side Harder
Dry eye can absolutely affect one eye more than the other. This often comes down to subtle differences between your two eyes: one eyelid may not close as completely during sleep, or you may sleep on one side, exposing that eye to more airflow overnight. Eyelid problems like a lid that turns slightly outward or inward increase tear evaporation on that side. The result is a burning, stinging, or sandy feeling that’s worse in one eye, particularly in the morning or after long stretches of screen time.
Infections and Pink Eye
An eye infection often starts in just one eye before spreading to the other. Viral pink eye produces watery discharge and frequently shows up alongside a cold or respiratory infection. Bacterial pink eye is thicker and messier, with yellow or green pus that can glue your eyelids shut overnight. Both cause redness, irritation, and the sensation that something is in your eye.
Allergic pink eye, by contrast, almost always affects both eyes at once and comes with intense itching, so if only your right eye hurts without much itchiness, an allergy is less likely the culprit.
Sinus Pressure Behind the Eye
Your sinuses sit directly behind and around your eye sockets, and when they’re inflamed, the pain can feel like it’s coming from the eye itself. Inflammation of the sphenoid and ethmoid sinuses (the ones deepest in your skull) causes pain behind and between the eyes. In early stages, sinus pain is typically one-sided before it spreads.
The telltale sign of sinus-related eye pain is that it gets worse when you bend forward or put your head below your heart. You may also notice tenderness when you press on your cheekbones or forehead, along with congestion, a runny nose, or postnasal drip. Once the infected material drains, the pain usually eases.
Cluster Headaches
Cluster headaches produce some of the most intense one-sided eye pain you can experience. They strike on the same side each time, and the pain is often described as a burning or piercing sensation in or around the eye. A single attack typically lasts 30 to 45 minutes, though it can range from 15 minutes to 3 hours. During a cluster period, headaches come daily, sometimes several times a day.
What sets cluster headaches apart from other causes is the collection of symptoms that come along with the pain: a red, watery eye on the affected side, a stuffy or runny nostril on the same side, facial sweating, a drooping eyelid, and swelling around the eye. If your right eye pain comes in these intense, predictable bursts with those accompanying symptoms, cluster headaches are a strong possibility.
Inflammation Inside the Eye
Several types of internal inflammation can cause deep, aching eye pain. One of the more common forms affects the front portion of the eye and produces pain, redness, light sensitivity, and blurred vision. You might notice that your pupil looks irregular or smaller than the other eye’s pupil. In some cases, a visible white layer of fluid collects at the bottom of the colored part of your eye.
A more concerning possibility is inflammation of the optic nerve, which carries visual signals to your brain. This causes a dull ache behind the eye that gets noticeably worse when you move your eye. It can also affect your vision, sometimes creating a blind spot in your central or side vision. Optic nerve inflammation sometimes occurs on its own but can also be linked to autoimmune conditions, so it warrants a thorough evaluation.
Styes and Blocked Glands
A stye is a red, painful bump on or near your eyelid caused by an infected oil gland. It looks and feels like a pimple and can make blinking uncomfortable. A related problem, a chalazion, forms when an oil gland in the eyelid becomes clogged without necessarily getting infected. Chalazia tend to be less painful but create a firm lump that can press on the eye and cause aching or blurred vision. Both are common and usually resolve on their own with warm compresses over a week or two.
When Eye Pain Is an Emergency
Acute angle-closure glaucoma is the scenario that warrants a trip to the emergency room. It happens when fluid pressure inside the eye spikes suddenly because the drainage angle gets blocked. The symptoms are dramatic: severe eye pain, blurred vision, halos around lights, a very red eye, and nausea or vomiting. Permanent vision damage can happen quickly without treatment.
Other situations that call for immediate care include sudden vision loss in one eye, eye pain after an injury or surgery, and any combination of severe pain with redness and nausea. These are not “wait and see” scenarios.
How to Narrow Down the Cause
The type of pain matters. A sharp, gritty feeling points toward something on the surface, like a scratch or foreign body. A dull ache behind the eye suggests sinus problems, optic nerve inflammation, or eyestrain. Throbbing pain that worsens when you bend over is classic for sinusitis. Intense, cyclical pain with tearing and nasal congestion on the same side fits the cluster headache pattern.
Timing matters too. Pain that came on suddenly after an activity (woodworking, sports, putting in contacts) is most likely a corneal abrasion or foreign body. Pain that builds gradually over days alongside cold symptoms may be sinus-related. Pain that recurs at the same time each day in agonizing bursts could be a cluster headache. Chronic, low-grade discomfort that’s worst in the morning or after screen use often points to dry eye.
Pay attention to what comes with the pain. Thick discharge means infection. Light sensitivity and blurred vision suggest inflammation inside the eye. Nausea and halos around lights raise the concern for a pressure spike. These accompanying symptoms are often more useful than the pain itself in figuring out what’s going on.