Blood in the eye is almost always caused by a tiny blood vessel breaking on the surface of the white of your eye, a condition called a subconjunctival hemorrhage. It looks alarming, producing a bright red patch that can spread across the white of the eye, but it’s painless and typically harmless. Less commonly, blood can pool inside the eye itself, which is a different situation that needs prompt attention.
The Most Common Cause: A Broken Surface Vessel
The clear membrane covering the white of your eye (the conjunctiva) is packed with tiny, fragile blood vessels. When one of these bursts, blood gets trapped beneath the surface and shows up as a vivid red splotch. You might notice it in the mirror or have someone else point it out, because it rarely causes any symptoms beyond its dramatic appearance. There’s no pain, no change in your vision, and no discharge.
Several everyday physical actions can trigger this by briefly spiking pressure in the veins around your eye:
- Coughing or sneezing forcefully, especially during a cold or allergy flare
- Straining while lifting something heavy or using the toilet
- Vomiting
- Rubbing your eye too hard
- Minor bumps or pokes to the eye area
Sometimes no obvious trigger exists at all. You go to sleep fine and wake up with a red eye. That’s normal and doesn’t mean something worse is going on.
Medications That Raise Your Risk
Blood thinners and drugs that reduce your blood’s ability to clot make these surface vessels more likely to bleed and slower to seal up. Warfarin and aspirin are the most common culprits. Newer oral anticoagulants carry similar risk. Supplements matter too: ginkgo biloba, omega-3 fish oil, and high-dose vitamin E all have mild blood-thinning properties. If you take any combination of these and notice recurring red patches on your eye, it’s worth mentioning to your doctor, not because the hemorrhage itself is dangerous, but because frequent episodes may signal your clotting balance needs a closer look.
When Blood Appears Inside the Eye
A subconjunctival hemorrhage sits on the white of the eye, outside the structures that affect your vision. A hyphema is fundamentally different. It’s blood collecting inside the front chamber of your eye, in the space between the clear cornea and the colored iris. Instead of a red patch on the white, you see blood pooling around or in front of your iris or pupil.
Hyphemas almost always result from direct trauma: a ball or puck striking the eye during sports, a bungee cord snapping back, a car accident, or a blow to the face. They hurt, and they often blur your vision. The key distinction is straightforward. If the blood appears to be on or near the colored part of your eye rather than on the white, or if you have pain or any change in vision alongside the redness, you need to be seen by an eye doctor or in an emergency department the same day. Hyphemas can raise the pressure inside the eye and, if untreated, damage your vision permanently.
Underlying Health Conditions
Occasional broken vessels on the eye surface happen to healthy people. Recurring ones can be a signal from your cardiovascular system. High blood pressure is one of the most important underlying factors. Chronic hypertension causes the small arteries in the eye to narrow over time, making them stiffer and more prone to breaking under sudden pressure changes. You can have elevated blood pressure for years without symptoms, so a pattern of eye hemorrhages sometimes leads to a diagnosis that was otherwise missed.
Diabetes affects eye blood vessels through a different mechanism. Persistently high blood sugar triggers chronic inflammation in the vessel walls and disrupts normal blood flow regulation. Over time, the vessels in the retina (the light-sensing tissue at the back of the eye) widen, weaken, and can leak or bleed. This process, called diabetic retinopathy, is a leading cause of vision loss. Surface hemorrhages on the white of the eye aren’t the same thing as retinal bleeding, but both reflect the toll that poorly controlled blood sugar takes on delicate vessels.
Bleeding disorders, whether inherited or caused by liver disease, are another less common but important factor. If you bruise easily elsewhere on your body and also get frequent eye hemorrhages, that pattern points toward a systemic clotting problem rather than simple bad luck with fragile vessels.
How Doctors Evaluate It
A straightforward subconjunctival hemorrhage usually needs nothing more than a visual inspection. A doctor can confirm the diagnosis just by looking at your eye. No imaging or specialized equipment is required for a single, painless episode with no vision changes.
If hemorrhages keep coming back, the workup expands. Your doctor will likely check your blood pressure, order blood tests to screen for clotting abnormalities, and review your medications. An eye exam may be done to rule out damage to deeper structures. For a suspected hyphema or any bleeding that involves the iris or pupil, an ophthalmologist will use a slit lamp (a high-powered microscope with a focused light) to examine the front chamber of the eye in detail and may measure the pressure inside the eye.
Healing Timeline
A subconjunctival hemorrhage follows a predictable course. The bright red patch will spread slightly over the first day or two as the trapped blood disperses, which can make it look worse before it looks better. Over the next one to three weeks, the color shifts from red to orange to yellow as your body gradually reabsorbs the blood, much like a bruise fading on your skin.
There’s no way to speed this up. Artificial tears can help if the area feels mildly scratchy, but the healing is purely a waiting game. The blood doesn’t enter your eye or affect your vision at any point during recovery. You don’t need to avoid screens, limit reading, or change your daily activities. If you wear contact lenses, it’s reasonable to leave them out until the redness has cleared, simply to avoid extra irritation.
Signs That Need Immediate Attention
Most blood in the eye resolves on its own, but certain combinations of symptoms change the picture entirely. Get evaluated the same day if you notice blood near your iris or pupil (the colored or black center of your eye), any blurriness or vision changes alongside the bleeding, eye pain beyond mild scratchiness, sensitivity to light, or bleeding that followed a significant impact to your eye or head. These features suggest bleeding inside the eye rather than on the surface, and the difference between the two determines whether you need treatment or simply time.