A blood clot in the eye usually refers to one of two conditions: a visible red patch on the white of the eye (subconjunctival hemorrhage) or a blockage inside a retinal vein that disrupts vision. The causes differ significantly depending on which type you’re dealing with, and so do the consequences. A red spot on the surface is almost always harmless. A clot inside the retina is a serious vascular event that can lead to lasting vision loss.
Two Different Conditions, Two Different Causes
When people say “blood clot in the eye,” they’re typically describing one of these:
- Subconjunctival hemorrhage: A tiny blood vessel breaks on the surface of the eye, creating a bright red patch on the white part. It looks alarming but rarely affects vision.
- Retinal vein occlusion (RVO): A blood clot partially or fully blocks a vein that drains blood from the retina, the light-sensitive tissue at the back of the eye. This can cause sudden, painless vision changes and requires prompt treatment.
The surface type is common and heals on its own. The retinal type is less common but far more serious. Understanding which one you’re dealing with matters, because the causes, risks, and next steps are completely different.
What Causes Surface Eye Bleeding
A subconjunctival hemorrhage happens when a small blood vessel in the clear membrane covering the white of your eye breaks open. Blood pools underneath and creates a vivid red spot that can cover a large area. It looks dramatic, but it’s roughly the same thing as a bruise under the skin.
The most common triggers involve brief spikes in blood pressure through your veins. Coughing hard, sneezing, vomiting, straining on the toilet, heavy lifting, or even rubbing your eye too aggressively can all do it. Wearing contact lenses and minor injuries to the eye or head are also frequent culprits. Blood-thinning medications make these hemorrhages more likely because they reduce your blood’s ability to clot quickly.
Less commonly, surface bleeding can signal an underlying health problem. Diabetes, high blood pressure, and blood clotting disorders all increase the risk. Repeated subconjunctival hemorrhages without an obvious trigger are worth investigating, since they can occasionally point to vascular disease or a bleeding disorder.
What Causes a Retinal Vein Occlusion
Retinal vein occlusion is a different situation entirely. It occurs when a clot forms inside one of the veins responsible for draining blood away from the retina. When that drainage gets blocked, blood and fluid back up, causing swelling and damage to the retinal tissue you rely on for vision.
The underlying mechanism involves damage to the blood vessel walls. Over time, conditions like high blood pressure and diabetes cause hardening and thickening of the arteries (atherosclerosis). In the eye, a hardened artery can physically compress the vein running alongside it. That compression changes how blood flows through the vein, creating the conditions for a clot to form: sluggish flow, turbulence, and eventually a blockage.
There are two types. Central retinal vein occlusion (CRVO) blocks the main vein draining the entire retina and tends to cause more widespread vision loss. Branch retinal vein occlusion (BRVO) blocks one of the smaller tributary veins and typically affects only part of the visual field. BRVO is more common of the two.
Risk Factors That Increase Your Chances
The biggest risk factors for retinal vein occlusion are the same ones that drive heart disease and stroke: high blood pressure, diabetes, and high cholesterol. These conditions damage blood vessel walls throughout your body, and the tiny vessels in the eye are especially vulnerable. Glaucoma, which increases pressure inside the eye, is another significant risk factor because that elevated pressure can compress retinal veins.
Age plays a major role. Retinal vein occlusion is most common in people over 50, when years of cumulative vascular damage start to take a toll. Smoking accelerates that damage by harming blood vessel walls and promoting clot formation. Blood clotting disorders, whether inherited or acquired, also raise the risk because they make clots more likely to form anywhere in the body, including the eye.
There’s a broader cardiovascular connection worth knowing about. Research from the American Heart Association found that people with diabetes who developed damage to their retinal blood vessels had a 60% higher risk of stroke compared to those with diabetes who didn’t have retinal vessel damage. In other words, a vascular event in the eye can be a warning sign that blood vessels elsewhere are in trouble too.
How Each Type Feels
A subconjunctival hemorrhage is painless. You might not even notice it until you look in a mirror or someone points it out. Your vision stays normal, and the red patch gradually fades over one to three weeks as your body reabsorbs the blood, often shifting from red to yellow before clearing completely.
Retinal vein occlusion is also painless, but the vision changes are unmistakable. You may notice sudden blurriness or distortion in one eye, dark spots or floaters, or a section of your visual field going dim or dark. These symptoms typically appear in one eye only and can develop over hours or happen all at once. Because there’s no pain, some people delay getting help, but rapid treatment makes a real difference in how much vision you keep.
How Retinal Vein Occlusion Is Treated
Treatment for retinal vein occlusion focuses on controlling the swelling that damages retinal tissue. The standard approach involves injections of medication directly into the eye that reduce fluid leakage from damaged blood vessels. These injections work by blocking a protein that triggers abnormal blood vessel growth and leakage.
Results from the SCORE2 clinical trial, reported by the National Institutes of Health, showed that patients treated with these injections gained an average of three lines of improvement on an eye chart after six months of monthly treatments. That improvement held up at the five-year mark, though some patients lost a small amount of acuity compared to their best result at one year.
The challenging reality is that retinal vein occlusion is a chronic condition. Most patients in the SCORE2 study still needed ongoing injections to control retinal swelling for at least five years. Treatment doesn’t cure the underlying blockage. It manages the consequences of it, preventing further damage and preserving the vision gains that were achieved early on.
For a subconjunctival hemorrhage, no treatment is needed. The blood clears on its own. Artificial tears can help if the eye feels scratchy, but the condition resolves without intervention.
Reducing Your Risk
Since the major causes of serious eye clots are the same conditions that drive heart disease, prevention looks similar. Keeping blood pressure and blood sugar in a healthy range protects the tiny vessels in your eyes as much as it protects the larger ones in your heart and brain. If you already have high blood pressure or diabetes, consistent management of those conditions is the most effective thing you can do.
Regular physical activity, at least 150 minutes of moderate exercise per week, improves circulation and cardiovascular health broadly. Staying well hydrated helps maintain normal blood volume and flow. A diet rich in fruits, vegetables, whole grains, and omega-3 fatty acids from fish supports healthy blood vessels. Smoking is one of the most controllable risk factors: it directly damages vessel walls and promotes clotting, and quitting reduces that risk.
If you’ve already had a retinal vein occlusion in one eye, your doctor will likely evaluate your cardiovascular health thoroughly, since the event suggests systemic vascular disease that could affect other organs. Managing those underlying conditions isn’t just about protecting your eyes. It’s about reducing your risk of stroke and heart attack as well.