A broken blood vessel in the eye, known medically as a subconjunctival hemorrhage, happens when one of the tiny blood vessels in the clear membrane covering the white of the eye ruptures and leaks blood into the space beneath it. The result is a vivid red patch that looks alarming but is almost always harmless. The vessels involved are extraordinarily small, with diameters averaging around 15 microns, so it does not take much force or pressure to breach one. What makes this so common is the sheer variety of triggers: everything from a hard sneeze to uncontrolled blood pressure to a particular medication can set one off.
Why the Eye’s Surface Vessels Are So Vulnerable
The conjunctiva is a thin, transparent tissue that drapes over the white of the eye and lines the inside of the eyelids. It is packed with tiny blood vessels that supply oxygen and nutrients to the eye’s surface. Research measuring these vessels has found their diameters range from roughly 9 to 24 microns, with an average around 15.5 microns.1Europe PMC. Quantitative assessment of conjunctival microvascular circulation of the human eye For perspective, a human hair is about 70 microns wide, so these vessels are a fraction of that. Walls this thin and delicate mean that even modest spikes in pressure or minor mechanical force can cause a rupture. Because the conjunctiva is also loosely attached to the eyeball, blood from a broken vessel spreads out beneath it, creating that flat, bright-red blotch rather than a raised bump.
Everyday Physical Triggers
The most common culprits are momentary surges in pressure that you might not even notice. A violent sneeze, a hard cough, straining during a bowel movement, heavy lifting, or vigorous vomiting all briefly spike venous pressure in the head and face. That sudden increase can be enough to pop one of those fragile conjunctival vessels. Rubbing your eyes aggressively is another frequent trigger; the mechanical shear on the surface vessels can tear one open. Some people wake up with a subconjunctival hemorrhage and have no idea what caused it, likely because they rubbed their eye in their sleep or pressed their face into a pillow at an awkward angle.
Direct trauma is the other obvious mechanical cause. A finger poke, a ball hitting the eye, a minor bump during sports, or even vigorous towel-drying near the eye can rupture a vessel. In younger people, trauma and contact lens use are the leading risk factors for these hemorrhages.2PubMed Central. Subconjunctival hemorrhage: risk factors and potential indicators Contact lenses can cause microtrauma to the conjunctiva during insertion, removal, or if a lens shifts out of position and scrapes the surface.
How Blood Pressure and Chronic Disease Change the Picture
While young, healthy people get subconjunctival hemorrhages from physical events, the pattern shifts with age. In older adults, the dominant risk factors are systemic vascular diseases: high blood pressure, diabetes, and hardening of the arteries.2PubMed Central. Subconjunctival hemorrhage: risk factors and potential indicators These conditions weaken blood vessel walls throughout the body, and the eye’s surface vessels are no exception.
Hypertension is the single most discussed systemic factor. Chronically elevated blood pressure puts continuous strain on vessel walls, making them more prone to spontaneous rupture. You may not feel high blood pressure, but a broken eye vessel can occasionally be the first visible sign that your blood pressure is running too high. That does not mean every red spot on your eye means you have hypertension, but if it keeps happening without an obvious physical trigger, checking your blood pressure is a reasonable first step.
Diabetes affects the eye’s vasculature in a more insidious way. Research on the conjunctival blood vessels of people with long-standing type 1 diabetes found that the smallest capillary-sized vessels became roughly 18% more tortuous compared with non-diabetic controls, while larger vessels actually became less tortuous over time.3PubMed. Diabetes and the tortuosity of vessels of the bulbar conjunctiva Tortuous, kinked vessels are structurally weaker and more susceptible to rupture. This remodeling of the microvasculature reflects the broader damage diabetes does to small blood vessels everywhere in the body, from the kidneys to the retina.
Medications and Supplements That Raise the Risk
Blood-thinning medications are a well-recognized contributor. A large nationwide study in Taiwan examined non-traumatic subconjunctival hemorrhages and found that aspirin use was significantly associated with these events.4PLOS ONE. Incidence of Non-Traumatic Subconjunctival Hemorrhage in a Nationwide Study in Taiwan from 2000 to 2011 The antiplatelet drugs clopidogrel and the anticoagulant warfarin also showed associations, though those were weaker after statistical adjustment. This makes intuitive sense: these drugs interfere with the blood’s ability to clot, so when a tiny vessel does break, the bleeding spreads more freely rather than being quickly plugged.
If you take any of these medications and notice recurring red spots on your eye, it does not mean you should stop the drug. Aspirin and warfarin are typically prescribed for serious cardiovascular reasons, and stopping them without medical guidance carries its own risks. But it is worth mentioning the eye bleeds to your doctor so they can decide whether any dosing adjustment makes sense.
Herbal supplements can sneak under the radar here. Ginkgo biloba, a popular over-the-counter supplement marketed for memory and circulation, inhibits platelet-activating factor. At least one documented case involved a patient with age-related macular disease who developed a spontaneous hemorrhage inside the eye while taking ginkgo biloba.5Europe PMC. Vitreous haemorrhage associated with Gingko biloba use in a patient with age related macular disease Many people do not think to mention supplements to their eye doctor, but anything that thins the blood or impairs clotting, whether prescription or herbal, can raise the chance of eye vessel ruptures. Fish oil in high doses and vitamin E supplements fall into the same category, though the evidence for those is less formally documented in eye-specific studies.
Contact Lenses and Eye Surface Health
Contact lens wear is a distinct risk factor for subconjunctival hemorrhage, especially in younger people.2PubMed Central. Subconjunctival hemorrhage: risk factors and potential indicators The repeated mechanical interaction between the lens edge and the conjunctiva creates low-level friction, and occasionally a vessel gives way. Lenses that fit poorly, that dry out, or that are worn past their replacement schedule are more likely to cause this. Inserting and removing contacts can also scrape the conjunctival surface if you are not careful, particularly if your hands are dry or you fumble the lens.
Beyond direct lens-related trauma, chronic eye surface conditions can change how the conjunctival blood vessels behave. Research on people with dry eye disease found that their conjunctival vessels were wider and carried faster blood flow compared with healthy eyes.6Europe PMC. Microvascular abnormalities in dry eye patients Vessel diameter in the dry eye group averaged about 22 microns compared with about 18 microns in controls. Wider, more engorged vessels under chronic inflammatory stress are plausibly more vulnerable to rupture, though studies have not yet directly measured whether dry eye patients get more subconjunctival hemorrhages. If you are a contact lens wearer who also struggles with dry eyes, the combination of mechanical irritation and inflamed, dilated surface vessels likely increases your risk more than either factor alone.
When It Keeps Happening
A single subconjunctival hemorrhage is almost never a cause for concern. It clears up on its own in one to three weeks as the blood is slowly reabsorbed, much like a bruise fading on your skin. No treatment is needed, and artificial tears can ease any mild irritation.
Recurrent or persistent episodes are a different story. When subconjunctival hemorrhages keep coming back, further investigation is warranted, including screening for high blood pressure, bleeding disorders, certain cancers affecting the eye or blood, and medication side effects.2PubMed Central. Subconjunctival hemorrhage: risk factors and potential indicators Bleeding disorders like hemophilia, von Willebrand disease, or platelet dysfunction make vessel ruptures more likely and the resulting hemorrhages more pronounced. Liver disease can also impair clotting factor production, leading to easier bleeding throughout the body, including in the eye. In rare cases, recurrent subconjunctival hemorrhages have been linked to blood cancers like leukemia, where abnormal blood cells disrupt normal clotting.
The practical takeaway: one episode with a clear trigger like a coughing fit or a minor eye rub does not need investigation. Multiple episodes over several months without an obvious cause, or a single episode that does not clear within three weeks, should prompt a visit to your doctor for a basic workup.
Surface Bleeding Versus Bleeding Inside the Eye
It is worth understanding that a broken blood vessel on the surface of the eye and bleeding inside the eye are entirely different conditions with very different levels of seriousness. A subconjunctival hemorrhage is superficial: the blood sits between the conjunctiva and the sclera (the white outer shell), and it does not affect your vision at all. It looks dramatic but is functionally harmless.
Bleeding inside the eye, such as vitreous hemorrhage, is a far more significant event. The vitreous is the gel-like substance that fills the interior of the eyeball. When blood leaks into it, you may see floaters, haze, cobweb-like shadows, or in severe cases, a sudden curtain-like loss of vision. Spontaneous vitreous hemorrhage occurs in roughly 7 per 100,000 people. The most common causes include diabetic retinopathy, which accounts for about a third of cases, and retinal tears, which account for another third.7Europe PMC. Vitreous Hemorrhage Retinal vein occlusion and posterior vitreous detachment make up most of the remaining cases.
The critical distinction for you as a patient is whether the hemorrhage affects your vision. A bright red patch on the white of your eye with perfectly normal sight is a subconjunctival hemorrhage and not an emergency. Any new floaters, flashing lights, hazy vision, or a shadow creeping across your visual field suggests bleeding inside the eye, which demands urgent evaluation. The surface appearance of the eye can look completely normal with an internal hemorrhage, so the visual symptoms are your main clue.
Less Obvious Contributing Factors
Alcohol consumption can contribute to subconjunctival hemorrhages in a couple of ways. Heavy drinking raises blood pressure acutely and, over time, can impair liver function enough to reduce the production of clotting factors. The combination of elevated pressure and slower clotting makes vessel rupture more likely. Some people notice they wake up with a red eye the morning after particularly heavy drinking, though few formal studies have isolated alcohol as a standalone cause of subconjunctival hemorrhage specifically.
Sleep deprivation and eye fatigue are anecdotally associated with broken eye vessels, though strong clinical evidence is thin. The more plausible mechanism is that tired, irritated eyes get rubbed more often, and rubbing is the real trigger. Similarly, prolonged crying can cause vessel ruptures, both from the mechanical act of wiping and pressing the eyes and from the facial pressure changes that accompany hard sobbing.
Pregnancy sometimes triggers subconjunctival hemorrhages, particularly during labor when women bear down with extreme force. The Valsalva maneuver during pushing creates tremendous venous back-pressure in the head, and the eye’s surface vessels are among the first to give way. This is harmless and resolves after delivery, though it can add to the general postpartum bewilderment.
What You Can and Cannot Do About Prevention
Since many triggers are involuntary, like sneezing or coughing, you cannot prevent every subconjunctival hemorrhage. But you can reduce the frequency if they keep recurring:
- Manage blood pressure: If your blood pressure is elevated, treating it reduces strain on every blood vessel in your body, including the delicate conjunctival ones.
- Avoid aggressive eye rubbing: If your eyes itch, use lubricating drops or cold compresses instead of grinding your knuckles into them.
- Handle contacts carefully: Make sure your lenses fit well, replace them on schedule, and keep your hands clean and moist during insertion and removal.
- Review medications with your doctor: If you are on aspirin, warfarin, or another blood thinner and getting frequent eye hemorrhages, your doctor may be able to adjust the dose or check your clotting levels.
- Disclose supplements: Mention ginkgo biloba, high-dose fish oil, or vitamin E to your eye care provider, especially if you are prone to eye bleeds.
Protective eyewear during sports or yard work is worth mentioning not because it prevents pressure-related hemorrhages but because it prevents the traumatic kind, a racquetball to the eye or a branch snapping back is a common and entirely avoidable cause.
Dry Eye, Screen Time, and Modern Vessel Stress
The rise in screen time has driven a parallel rise in dry eye symptoms, and as noted earlier, dry eye disease is associated with changes in conjunctival vessel structure. People with dry eye have wider, faster-flowing conjunctival blood vessels compared to those with healthy eyes.6Europe PMC. Microvascular abnormalities in dry eye patients Chronic surface inflammation from inadequate tear coverage keeps the conjunctival vessels in a dilated, stressed state. Whether this directly causes more hemorrhages has not been definitively proven, but the vascular changes make it biologically plausible.
People who spend long hours at screens blink less frequently, which accelerates tear film evaporation and triggers a cycle of dryness, irritation, and rubbing. The rubbing, rather than the screen itself, is the likely mechanical trigger for any hemorrhage. Using artificial tears during long computer sessions, taking breaks to blink deliberately, and adjusting screen brightness and distance are simple interventions that address both the dry eye symptoms and the urge to rub. None of this is dramatic, but if you find yourself with a red eye after a long day of screen work, the causal chain probably ran from dry eyes to irritation to rubbing to a popped vessel, not from the screen directly.