Every eye has blood vessels. The thin, clear membrane covering the white of your eye (the conjunctiva) is laced with tiny blood vessels that deliver oxygen and nutrients to the eye’s surface. Most of the time these vessels are so small you can’t see them, but when they dilate or break, they become suddenly and sometimes dramatically visible. If you’re noticing them for the first time, the cause is almost always harmless.
Why Eye Blood Vessels Are Normally Invisible
The conjunctiva is nearly transparent, and the blood vessels running through it are extremely fine. They sit against the white backdrop of the sclera, so when they’re at their normal width, they barely register. You could photograph them with a macro lens, but your mirror won’t show much.
What changes is their size. When those vessels widen (dilate), they hold more blood and become visible as red or pink lines. When one actually ruptures, blood pools under the conjunctiva and creates a vivid red patch. These are two different things, and understanding which one you’re seeing helps explain what’s going on.
Dilated Vessels: The Most Common Cause of Redness
When your eyes look “bloodshot,” you’re seeing blood vessels that have expanded in response to irritation or inflammation. The vessels haven’t broken. They’ve simply widened to increase blood flow, the same way skin flushes when it’s warm. Common triggers include:
- Dry eyes and screen time. Blinking keeps your eye surface lubricated. During prolonged computer use, your blink rate can drop from roughly 18 blinks per minute to as few as 3 or 4. Less blinking means a drier surface, which triggers redness, burning, and a gritty feeling.
- Allergies. Pollen, pet dander, and dust provoke an inflammatory response in the conjunctiva that dilates vessels and causes itching.
- Smoke, wind, and dry air. Environmental irritants strip moisture from the eye’s surface and cause the same dilation response.
- Lack of sleep. Fatigue reduces tear production and increases strain, leaving vessels more prominent in the morning.
- Alcohol. It dilates blood vessels throughout the body, including in the eyes.
In all of these cases, the redness fades once the irritant is removed. Artificial tears can help by restoring moisture to the eye’s surface. If you spend hours on screens, consciously blinking more often or taking periodic breaks makes a real difference.
Broken Blood Vessels: The Bright Red Patch
A subconjunctival hemorrhage looks far more alarming than dilated vessels. Instead of general redness, you’ll see a solid, bright red blotch on the white of your eye, almost like a bruise. It happens when a small conjunctival vessel ruptures and blood leaks into the space beneath the membrane.
The triggers are surprisingly mundane. A hard sneeze, a coughing fit, straining on the toilet, vomiting, heavy lifting, or even rubbing your eye too vigorously can briefly spike the pressure in your veins enough to pop one of these tiny vessels. Contact lens wear is another common cause. Sometimes it happens for no obvious reason at all, especially during sleep.
Despite its appearance, a subconjunctival hemorrhage is painless and doesn’t affect your vision. It typically clears on its own within a few days to a few weeks as the blood is gradually reabsorbed. No treatment is needed, though artificial tears can help if the area feels mildly scratchy. The red patch may shift color as it heals, turning yellow or green like a fading bruise before disappearing completely.
Contact Lenses and New Vessel Growth
Long-term contact lens wear can cause something different from both dilation and hemorrhage: the actual growth of new blood vessels into the cornea, the clear dome over your iris. The cornea normally has no blood vessels at all. It gets its oxygen directly from the air. When a contact lens sits over the cornea for extended periods, it reduces oxygen delivery, and the body responds by growing tiny new vessels inward from the edges to compensate.
This is most common with extended-wear lenses and lenses that aren’t very breathable. Early on, these new vessels are fine and superficial. Over time, if the oxygen deprivation continues, they can grow deeper into the cornea and potentially affect vision. Switching to higher-oxygen lenses, reducing daily wear time, and giving your eyes regular breaks without lenses are the main ways to prevent this.
Health Conditions That Make Vessels More Fragile
A single broken blood vessel in your eye is rarely a sign of anything serious. Recurrent episodes are worth paying attention to. In younger people, the most common culprits are trauma and contact lens use. In older adults, the pattern shifts toward systemic vascular conditions.
High blood pressure is the most frequently identified risk factor for repeated subconjunctival hemorrhages. Diabetes and hardening of the arteries (arteriosclerosis) also weaken vessel walls over time, making them more likely to rupture under minimal stress. The fragility of conjunctival vessels increases with age for the same reasons blood vessels elsewhere in the body become more fragile.
Blood clotting disorders, low platelet counts, and certain blood cancers like leukemia can also cause bleeding in the conjunctival vessels. These are uncommon causes, but if you’re getting frequent unexplained hemorrhages, a blood pressure check and basic blood work can rule out or identify an underlying issue.
Medications That Increase Eye Bleeding
Blood thinners are a well-known contributor. Aspirin, warfarin, and newer anticoagulants all reduce your blood’s ability to clot, which means even a minor vessel rupture can produce a more visible hemorrhage that takes longer to resolve. Some supplements have similar effects. Ginkgo biloba, for instance, has been linked to intraocular bleeding in case reports.
If you’re on blood thinners and notice occasional red patches in your eye, this is a recognized side effect rather than a sign of a new problem. But mention it to your prescriber so they can confirm your dosing is appropriate.
Signs That Need Prompt Attention
Most visible eye blood vessels, whether dilated or broken, resolve without any intervention. The situations that call for immediate care are specific and distinct from ordinary redness:
- Sudden vision changes alongside redness
- Eye pain that feels deep, not just surface irritation
- Sensitivity to light that wasn’t there before
- A severe headache or fever accompanying the redness
- Swelling in or around the eye
- Seeing halos around lights
- Redness caused by a chemical splash or foreign object
These combinations can signal conditions like acute glaucoma, uveitis, or infection that need treatment quickly to protect your vision. Redness alone, without pain or vision changes, is almost never an emergency.