Why Do I Have a Blood Clot in My Eye and Is It Serious?

A bright red patch on the white of your eye is usually a subconjunctival hemorrhage, a harmless burst blood vessel that clears up on its own within a couple of weeks. When the phrase “blood clot in the eye” refers to a blockage inside the retinal blood vessels, though, the situation is genuinely serious, with potential for permanent vision loss and connections to cardiovascular disease elsewhere in your body. The distinction between these two scenarios matters enormously, and recognizing which one you’re dealing with can determine whether you need to see a doctor today or simply wait it out.

The Surface Kind Is Almost Always Harmless

The most common “blood clot in the eye” is a subconjunctival hemorrhage: a small blood vessel breaks underneath the clear membrane covering the white of your eye, and blood pools in the space between. It looks dramatic, sometimes turning a large patch of the white of your eye solid red. But there’s no pain, no vision change, and no treatment needed. It happens from coughing, sneezing, straining, rubbing your eyes, or sometimes for no obvious reason at all. The blood reabsorbs over one to three weeks, often shifting from red to yellow before fading completely.

You should mention it to your doctor if subconjunctival hemorrhages keep recurring, especially if you take blood thinners or have high blood pressure, since frequent episodes can signal that your blood pressure or clotting needs attention. But a single episode in an otherwise healthy person is about as medically significant as a bruise on your arm.

When the Problem Is Inside the Retina

The more serious kind of eye blood clot happens when a blood vessel inside the retina, the light-sensitive tissue lining the back of your eye, gets blocked. These blockages fall into two main categories. A retinal vein occlusion (RVO) happens when a vein draining blood out of the retina gets obstructed. A retinal artery occlusion (RAO) happens when an artery feeding blood into the retina gets blocked. Both cause sudden, painless changes in vision, but the urgency and outlook differ between them.

With a retinal vein occlusion, blood can still flow into the retina but can’t drain out efficiently. Pressure builds, blood and fluid leak into the surrounding tissue, and your vision becomes blurry or distorted, sometimes with dark spots. This can affect a branch of the retinal vein (a branch retinal vein occlusion, or BRVO) or the main central vein (a central retinal vein occlusion, or CRVO). CRVO tends to cause more severe vision loss than BRVO because the entire retina’s drainage is compromised rather than just one section.

Retinal artery occlusions are rarer and more urgent. When blood flow into the retina is cut off, the retinal cells begin to die from oxygen starvation within minutes to hours, much like what happens to brain tissue during a stroke. The American Heart Association classifies central retinal artery occlusion as a form of acute ischemic stroke and has identified it as a warning sign of further cerebrovascular and cardiovascular events.¹ The typical symptom is sudden, dramatic, painless vision loss in one eye. If this happens to you, it is a medical emergency.

What Causes Retinal Blood Vessels to Block

The most common underlying cause for both retinal vein and artery occlusions is cardiovascular disease, particularly high blood pressure. A large study found that people with stage 2 hypertension had about a 32% higher risk of retinal vascular occlusion compared to people with normal blood pressure, with retinal vein occlusions showing the strongest and most consistent link.² Diabetes adds another layer of risk: research has found that in people with diabetes, higher fasting blood sugar and higher systolic blood pressure are the primary factors linked to retinal vein occlusion, while in people without diabetes, the main contributors include higher diastolic blood pressure and higher body mass index.³

The anatomy of the blood vessels inside the eye also plays a role. In the retina, arteries and veins cross over each other at various points. Research has shown that in people who develop branch retinal vein occlusions, the veins are more narrowed at these crossing points compared to healthy eyes, and this narrowing appears even in the unaffected fellow eye, suggesting it may be a pre-existing structural vulnerability rather than something that develops only at the time of the blockage.⁴ In simple terms, if your retinal arteries press more firmly against the veins where they cross, blood flow slows in the vein, creating conditions ripe for a clot.

The Glaucoma Connection

Glaucoma is one of the strongest eye-specific risk factors for retinal vein occlusion. A meta-analysis combining data from multiple studies found that people with glaucoma had about four times the odds of developing RVO compared to those without it. The link was strongest for central retinal vein occlusion, where glaucoma was associated with roughly six times the odds, and somewhat lower for branch vein occlusions at about two and a half times the odds.⁵ The relationship between the two conditions likely runs through shared vascular pathways and mechanical factors that damage both the optic nerve and the retinal veins.⁶

Interestingly, research using genetic analysis methods has suggested that the link between elevated eye pressure and retinal vein occlusion is mostly mediated through glaucoma itself. One study estimated that over 90% of the effect of high intraocular pressure on RVO risk operates through glaucoma, meaning it may be the structural damage that glaucoma causes to the optic disc and surrounding vessels that makes the vein vulnerable, rather than the pressure alone.⁷ If you already have glaucoma, this is one more reason to stay on top of treatment.

Young Adults Face a Different Risk Profile

Retinal vein occlusions typically affect older adults, which is why the cardiovascular risk factors dominate the picture. When these blockages occur in younger people, the cause is often different. In patients aged 45 and under, clotting disorders become a major factor. One study found that resistance to activated protein C, antiphospholipid antibodies, and deficiencies in anticoagulant proteins were all independent risk factors for retinal vein occlusion in younger patients.⁸ Research on young RVO patients has found that about a quarter had abnormal results on hypercoagulable workup, with genetic mutations affecting folate metabolism among the most frequent findings.⁹

In another study specifically looking at young people with central retinal vein occlusion, roughly one in nine had a coagulation disorder, with elevated homocysteine levels being the most common abnormality.¹⁰ The practical takeaway: if you’re under 45 and develop a retinal vein occlusion, expect your doctor to order an extensive blood workup looking for hidden clotting problems, even if your blood pressure and cholesterol are perfectly normal. Nearly half of young patients with RVO have at least one systemic risk factor, and about a third have two or more.⁹

Medications That Can Raise the Risk

Certain medications have been flagged as potential contributors to retinal vein occlusion. An analysis of nearly two decades of adverse-event reports submitted to the FDA identified several drug classes associated with RVO. Estrogen-containing medications, including some oral contraceptives, are among them. The proposed mechanism involves estrogen’s effect on blood clotting: high estradiol levels can make the blood more prone to forming clots, and that prothrombotic shift can affect even the small veins of the retina. Some newer oral contraceptives containing drospirenone carry a higher risk of venous blood clots elsewhere in the body, and researchers suspect a related risk for retinal veins as well.¹¹ This doesn’t mean hormonal contraceptives are dangerous for your eyes in most cases, but if you have other risk factors for clotting, it’s worth discussing with your doctor.

What Happens If a Retinal Vein Occlusion Is Left Untreated

The immediate concern with a retinal vein occlusion is usually macular edema, which is swelling in the central part of the retina responsible for sharp, detailed vision. When blood backs up behind a blocked vein, fluid leaks into the macula, blurring and distorting your central vision. RVO is actually the second most common retinal vascular disorder, and macular edema is one of its most frequent complications, along with the growth of abnormal new blood vessels and bleeding inside the eye.¹²

If the blockage is severe enough to starve the retina of oxygen, the eye responds by growing new, fragile blood vessels in a process called neovascularization. These new vessels are structurally abnormal and can bleed into the eye or grow into the drainage structures that regulate eye pressure. When abnormal vessels invade the iris or the drainage angle at the front of the eye, they can trigger a particularly aggressive form of elevated eye pressure called neovascular glaucoma, which is driven by severe retinal ischemia and can cause rapid, painful vision loss.¹³ This cascade from blocked vein to abnormal vessel growth to secondary glaucoma is one of the key reasons timely treatment matters.

How Retinal Vessel Occlusions Are Treated

For retinal vein occlusions, the mainstay of treatment is injections of anti-VEGF medication directly into the eye. VEGF is a protein the body produces in response to oxygen deprivation, and while its job is to stimulate blood vessel growth, in the retina it also increases vascular leakage, worsening macular edema. Anti-VEGF injections reduce swelling and can improve vision. In clinical practice, patients treated with anti-VEGF injections for macular edema from RVO gained an average of about two lines of visual acuity on a standard eye chart.¹⁴ A meta-analysis of randomized trials found anti-VEGF injections alone outperformed steroid injections or combination therapy in both reducing macular thickness and improving visual acuity.¹⁵

Steroid implants injected into the eye are another option, particularly for patients who don’t respond well to anti-VEGF therapy or who have difficulty keeping up with the frequent injection schedule anti-VEGF requires. A sustained-release dexamethasone implant can reduce macular swelling for months at a time. One randomized study found that adding laser treatment on top of a dexamethasone implant for branch retinal vein occlusion did not provide extra benefit and might actually compromise long-term visual outcomes, suggesting the steroid implant works best on its own.¹⁶

For retinal artery occlusions, the approach is fundamentally different because the retina is being starved of blood rather than flooded with it. There is no universally proven treatment to restore vision once a central retinal artery occlusion has occurred, which is why speed matters so much. Some acute interventions aim to dislodge the clot or restore flow, but the evidence for most of these remains limited. What is clearly established is the need for an urgent systemic workup. The EAGLE study found a previously undiagnosed cardiovascular risk factor in 78% of patients presenting with central retinal artery occlusion, and the most common finding was severe narrowing of the carotid artery on the same side, detected in 40% of patients. Only 3% of those patients had been previously identified as having significant carotid narrowing.¹⁷ In other words, the retinal artery blockage may be the first sign that you’re at high risk for a stroke or heart attack.

How Long-Term Treatment Affects Daily Life

One aspect of retinal vein occlusion that doesn’t get discussed enough is the treatment burden. Anti-VEGF therapy isn’t a one-and-done procedure. Many patients need injections every four to eight weeks, sometimes for years. A study surveying patients with RVO and diabetic macular edema found that each injection appointment, including travel, took an average of four and a half hours. Over a six-month period, RVO patients spent roughly 13 and a half hours just on injection visits.¹⁸ That’s a significant time commitment that can make it hard for working adults to keep up, and missed appointments can mean a setback in the progress your eye has made.

Even with consistent treatment, real-world outcomes are humbler than what the best clinical trials report. An analysis of clinical data found that anti-VEGF therapy failed to provide sufficient benefit in roughly half of patients with macular edema from RVO after three years of treatment.¹² That figure reflects real-world conditions, including inconsistent follow-up and individual variation in disease severity, but it underscores that treatment manages the condition rather than cures it. Long-term studies show that treated eyes do gain significant improvement in visual acuity scores, but the retina’s overall electrical function, measured by electroretinography, tends to decline over time regardless of treatment.¹⁹ This gradual decline in underlying retinal health is why ongoing monitoring matters even when your vision seems stable.

When to See a Doctor and How Quickly

The speed at which you need medical attention depends entirely on your symptoms. If you see a red patch on the white of your eye with no vision changes, no pain, and no sensitivity to light, you’re almost certainly looking at a subconjunctival hemorrhage. Monitor it for a couple of weeks. If it doesn’t fade, or if you get them repeatedly, mention it at your next doctor’s visit.

Seek same-day evaluation if you notice any of these:

Sudden blurry vision: especially in one eye, even if it’s partial or affects only part of your visual field.
Dark spots or missing areas: a shadow or curtain-like effect in your vision, or a patch that seems blocked out.
Sudden total vision loss: in one eye, this is a potential retinal artery occlusion and warrants emergency care, similar to the urgency of stroke symptoms.
Floaters with flashes: a sudden shower of new floaters or flashes of light alongside vision changes can indicate bleeding inside the eye from a vein occlusion or other serious conditions.

The key pattern is this: surface redness alone is rarely urgent, but any change in what you can see calls for prompt evaluation. Your eye doctor can distinguish between a harmless surface bleed and something deeper using relatively straightforward examination tools. Optical coherence tomography and fluorescein angiography can map the blood flow in your retinal vessels and reveal blockages, areas of swelling, and any abnormal new vessel growth with high precision.²⁰ Newer imaging modalities like OCT angiography can detect subtle changes in the capillary network of the macula without even needing a dye injection, making screening faster and less invasive.

What an Eye Clot Reveals About the Rest of Your Health

Perhaps the most important thing about a retinal vessel occlusion is what it says about your body beyond your eye. The retina is the one place in the body where doctors can directly observe blood vessels without surgery, and a clot there often reflects the same vascular damage happening in vessels you can’t see. The finding that 78% of patients with central retinal artery occlusion had an undiagnosed cardiovascular risk factor is striking: for many of those patients, the eye event was the first warning that something was wrong systemically.¹⁷

For retinal vein occlusions, the systemic signal is similar if somewhat less acute. Uncontrolled hypertension, undiagnosed diabetes, and elevated cholesterol are all common findings when doctors investigate the underlying cause of an RVO. This is why a retinal vein or artery occlusion often triggers a full cardiovascular workup, including blood pressure measurement, blood sugar and lipid testing, carotid artery imaging, and sometimes a cardiac evaluation. The eye event itself may be manageable, but the vascular disease driving it can be life-threatening if left unaddressed. Treating the eye without investigating the body is like fixing a leak in one room while ignoring the rising water throughout the house.