A blood clot or red patch in your eye is almost always a subconjunctival hemorrhage, a harmless burst blood vessel on the surface of the white of your eye. It looks alarming, often a bright red blotch that seems to appear out of nowhere, but it typically clears on its own within one to three weeks without any treatment. Less commonly, blood can collect inside the eye itself or a clot can block a blood vessel in the retina, and those situations do need medical attention.
The Most Common Type: A Broken Surface Vessel
The white part of your eye is covered by a thin, clear membrane called the conjunctiva. Tiny blood vessels run through it, and when one of them breaks, blood pools underneath the membrane with nowhere to go. The result is a flat, vivid red patch that can cover a small area or spread across most of the white of your eye. It looks dramatic, but the blood is trapped in a shallow layer on the surface. It doesn’t reach the inside of your eye or affect your vision.
This happens more often than most people realize. You might notice it first thing in the morning when you look in the mirror, with no memory of anything that could have caused it. That’s normal. The vessel can break during sleep or from something so minor you didn’t register it.
What Causes a Surface Blood Vessel to Break
Anything that briefly spikes the pressure in the small veins of your eye can pop a vessel. The most common triggers are:
- Coughing, sneezing, or vomiting, especially a prolonged bout
- Straining while lifting something heavy, pushing, bending forward, or using the toilet
- Rubbing your eye too hard
- A bump or poke to the eye, even a minor one
High blood pressure is the most significant ongoing risk factor. When blood pressure stays elevated, the tiny vessels throughout your body, including the ones in your eye, become more fragile and more likely to rupture. Blood-thinning medications and over-the-counter anti-inflammatory drugs like aspirin or ibuprofen also increase the risk, not because they cause the vessel to break, but because they make the bleeding spread more once it does. Contact lens wearers and people who take certain supplements like fish oil or vitamin E in high doses may notice these bleeds more frequently for the same reason.
Blood Inside the Eye Is Different
A subconjunctival hemorrhage sits on the surface. Blood that collects inside the eye, in the fluid-filled space between the cornea and the iris (the colored part), is called a hyphema. This usually results from a direct blow to the eye, like getting hit by a ball, an elbow, or a car airbag. It can also happen after eye surgery.
A hyphema looks different from a surface bleed. You may see a visible layer of blood pooling at the bottom of the iris, and your vision is often blurry or partially blocked. Pain and sensitivity to light are common. The concern with a hyphema is that blood cells trapped in this space can clog the eye’s internal drainage system, raising pressure inside the eye. In one large study of 235 cases, about 13.5% of people with small hyphemas developed elevated eye pressure, compared with 52% of those whose bleeding filled more than half the space. People with sickle cell disease are at especially high risk because their red blood cells can become rigid inside the eye, making the drainage problem worse. Left untreated, the elevated pressure can damage the optic nerve and lead to glaucoma.
If you suspect a hyphema, meaning you took a hit to the eye and now see blood pooling behind the cornea, blurry vision, or significant pain, that warrants same-day evaluation by an eye doctor.
Clots That Block Retinal Blood Vessels
The retina, the light-sensitive tissue lining the back of your eye, has its own network of blood vessels. A clot can block the main vein draining blood from the retina (central retinal vein occlusion) or one of the smaller branch veins (branch retinal vein occlusion). Unlike the other types, you won’t see redness in the mirror. Instead, the hallmark is sudden, painless vision loss or blurriness in one eye, sometimes affecting your entire field of vision and sometimes just a portion of it.
Retinal vein occlusions are closely tied to cardiovascular health. The same factors that cause blood clots in other parts of your body, high blood pressure, diabetes, high cholesterol, and smoking, increase the risk of a clot forming in the retinal veins. They’re most common in people over 50. If you experience sudden vision changes in one eye, especially without pain or redness, it needs prompt medical evaluation. An eye doctor can examine the retina directly and use imaging to see whether a vein is blocked and how much of the retina is affected.
How Surface Bleeds Heal
A subconjunctival hemorrhage follows a predictable pattern. The bright red patch gradually shifts to orange, then yellow, then fades completely as your body reabsorbs the blood. The whole process takes about one to three weeks depending on how large the bleed is. You don’t need drops, medication, or any special care. Some people find that artificial tears help with mild scratchiness or irritation, but the bleed itself resolves on its own.
The patch may actually look worse before it looks better, spreading out across a wider area in the first day or two before it starts to fade. This is just the blood dispersing under the membrane and is not a sign that the bleeding is continuing.
Reducing Your Risk of Recurrence
If you keep getting subconjunctival hemorrhages, the most productive thing you can do is check your blood pressure. Uncontrolled hypertension is the single most common underlying factor in people who experience these bleeds repeatedly. Getting your blood pressure into a healthy range significantly lowers the chance of another one.
Beyond that, try to minimize the mechanical triggers. Be gentle when rubbing your eyes, or better yet, avoid rubbing them altogether. If you have seasonal allergies that make your eyes itchy, treating the itch with antihistamine drops reduces the urge to rub. If you’re straining frequently during bowel movements, increasing your fiber and water intake helps. And if you’re taking blood thinners or regular aspirin, it’s worth mentioning the recurrent eye bleeds at your next appointment so your doctor can weigh the risks and benefits.
Signs That Need Prompt Attention
A painless red patch on the white of your eye, with normal vision and no discharge, is almost certainly a straightforward subconjunctival hemorrhage. You can safely wait and watch it fade. But certain symptoms point to something more serious:
- Pain in or around the eye, especially after an injury
- Any change in vision, including blurriness, dark spots, or partial vision loss
- Blood visible behind the cornea, pooling in front of the iris
- Sensitivity to light
- Bleeding that follows a significant blow to the face or eye
- Recurrent bleeds happening more than two or three times a year
Any of these warrants an eye exam, not because the outcome is always serious, but because the conditions they suggest (hyphema, retinal vein occlusion, uncontrolled blood pressure) are treatable when caught early and more difficult to manage when they’re not.