Can Blood Thinners Cause Blurry Vision?

Blood thinners can contribute to blurry vision, though the connection is usually indirect. These medications increase the risk of bleeding inside the eye, and when blood pools in or around the retina, vision can become hazy, distorted, or partially blocked. The risk is low for most people, but it rises sharply in those with certain pre-existing eye conditions, and the type of blood thinner matters more than many patients realize.

How Bleeding Inside the Eye Blurs Vision

Blood thinners work by slowing your body’s ability to form clots. That is helpful for preventing strokes and heart attacks, but it means that any bleed, anywhere in the body, can be harder to stop and potentially larger than it would otherwise be. The eye has a rich network of tiny, delicate blood vessels, and when one of those vessels leaks, blood can collect in spaces where it interferes with the light path to the retina.

The most vision-threatening type of intraocular bleeding is vitreous hemorrhage, where blood leaks into the gel-like substance filling the center of the eye. Even a small amount of blood in the vitreous can scatter light and make everything look foggy or reddish. A study of patients experiencing an acute posterior vitreous detachment found that those taking aspirin, clopidogrel, or warfarin had vitreous hemorrhage about 43% of the time, compared with 31% for patients not on those medications.¹ That is a meaningful difference, and vitreous hemorrhage is one of the more common reasons a person on blood thinners might suddenly notice blurred or cloudy vision.

Retinal and choroidal hemorrhages are less common but potentially more damaging. Blood beneath the retina can destroy the light-sensitive cells responsible for central vision, and even surgical removal of the blood often cannot fully restore what was lost.² A review of adverse-event reports to the World Health Organization’s global database found significant associations between both warfarin and newer oral anticoagulants and all three types of intraocular hemorrhage: vitreous, retinal, and choroidal.³

Then there is subconjunctival hemorrhage, the bright-red patch that appears on the white of the eye. This looks alarming but is almost always harmless. In a study of warfarin patients, these bleeds occurred at a low rate and none resulted in any lasting eye problems.⁴ A subconjunctival hemorrhage does not affect vision because the blood sits on the surface, not inside the eye where light travels. If you are on blood thinners and wake up with a red splotch on your eye but your vision is fine, that is the likely explanation, and it usually resolves on its own.

Which Blood Thinners Carry the Highest Eye-Bleeding Risk

Not all blood thinners are equal when it comes to the eyes. Warfarin, the older vitamin K antagonist that has been around for decades, appears to carry a higher overall risk of intraocular bleeding than the newer direct oral anticoagulants (sometimes called DOACs or NOACs), which include medications like rivaroxaban, dabigatran, apixaban, and edoxaban. A systematic review and meta-analysis pooling data from major clinical trials found that patients randomized to newer oral anticoagulants had roughly a 22% lower relative risk of intraocular bleeding compared with those on warfarin.⁵

The picture gets more nuanced when you look at specific newer agents. In the WHO’s adverse-event database, rivaroxaban showed the strongest signal for retinal and vitreous hemorrhage among the newer drugs, while warfarin had the strongest association with choroidal hemorrhage, the deepest and often most destructive type.³ These are signals from spontaneous adverse-event reports rather than controlled trials, so they do not pin down exact risk, but they give a general sense of which drugs are being linked to which eye complications. A separate large analysis comparing newer agents with older antiplatelet drugs in real-world patients found a modest decrease in intraocular hemorrhage risk over a full year for those on newer anticoagulants.⁶

Antiplatelet drugs like aspirin and clopidogrel are sometimes lumped in with “blood thinners” in everyday conversation, even though they work differently than anticoagulants. They still increase the chance of eye bleeding. The vitreous hemorrhage study mentioned earlier included aspirin and clopidogrel users alongside warfarin users, and all showed higher rates of hemorrhage than people not on any antithrombotic medication.¹ A review of ophthalmic complications with newer direct oral anticoagulants documented cases of large submacular hemorrhage, vitreous hemorrhage, and recurrent hyphema, with several patients needing surgical intervention to remove blood from the eye.⁷

Why Pre-Existing Eye Conditions Change the Equation

For most healthy eyes, the absolute risk of a vision-threatening bleed while on blood thinners is small. The calculus changes substantially if you already have a condition that makes the blood vessels in your eye fragile or abnormal. Age-related macular degeneration, particularly the “wet” form where abnormal blood vessels grow beneath the retina, is the standout example.

In people with wet AMD, those vessels are already prone to leaking. Add an anticoagulant or antiplatelet drug and the bleeds tend to be much larger. One study found that patients with AMD who were on antithrombotic therapy had subretinal hemorrhages averaging nearly ten disc areas in size, compared with about three disc areas for AMD patients not on blood thinners.⁸ Both antiplatelet and anticoagulant therapy independently correlated with larger hemorrhage size, and having high blood pressure on top of the blood thinners made things worse still. A large subretinal hemorrhage in AMD can permanently damage the central vision through toxic effects of trapped blood on the photoreceptor cells.²

If you have been diagnosed with wet AMD and your doctor is considering starting you on a blood thinner (or you are already on one), this is worth a conversation between your ophthalmologist and the prescribing physician. The decision is rarely straightforward: the blood thinner is typically there for a good reason, like preventing a stroke, and stopping it creates its own risks. But knowing the eyes are vulnerable can influence the choice of drug, the target intensity, and how frequently you get eye exams.

When Blurry Vision Signals Something More Serious

There is an important scenario that has nothing to do with bleeding inside the eye itself. Blood thinners are most often prescribed because a person has a condition that puts them at risk of blood clots, like atrial fibrillation. If the anticoagulation is not adequate, a clot can travel to the brain and block blood flow to the visual processing areas, causing sudden vision changes.

A well-documented case illustrates this: a 76-year-old man on warfarin for atrial fibrillation presented with blurred vision that had started the day before. His blood-clotting level was far above the therapeutic range, and examination revealed he had lost vision in the left half of his visual field in both eyes, a pattern consistent with a stroke affecting the right side of the brain where visual information is processed.⁹ This type of visual field loss can be mistaken for a general blurring of vision, especially if the person does not realize they have lost vision on one side rather than having cloudy vision overall.

The practical takeaway: if you are on a blood thinner and experience sudden blurry vision, especially if it is accompanied by headache, difficulty speaking, weakness on one side, or confusion, treat it as a potential stroke and seek emergency care immediately. Even isolated visual changes that come on abruptly deserve urgent evaluation, because a small stroke limited to the visual areas of the brain might not produce any other obvious symptoms.

On the other side of the coin, severe or chronic bleeding caused by blood thinners elsewhere in the body can lead to profound anemia, which itself can damage the optic nerve. A case report described a 65-year-old woman with severe anemia from chronic gastrointestinal bleeding who developed optic nerve infarction in both eyes, causing significant vision loss.¹⁰ This is rare, but it highlights that the visual effects of blood thinners can come through roundabout pathways, not just direct bleeding in the eye.

Non-Bleeding Visual Side Effects

Bleeding is the most studied and best-understood way blood thinners affect vision, but it is not the only one. Pharmacovigilance data from large adverse-event reporting systems have flagged some newer anticoagulants for visual side effects that do not appear to involve hemorrhage at all. A study mining the FDA’s adverse-event reporting database flagged apixaban for a signal associated with visual impairment, while edoxaban showed a signal for diplopia (double vision).¹¹

These findings come from spontaneous reports, not controlled trials, so they do not prove the drugs caused the symptoms. People taking anticoagulants tend to be older and to have conditions like high blood pressure and diabetes that independently affect vision. Still, the signals are worth knowing about. If you start a new blood thinner and notice visual changes that do not look like a red eye or a floater, mention it to your prescriber. Visual impairment, blurred vision, and double vision all appear in the post-marketing profiles of several anticoagulants, even if the labels do not highlight them prominently.

Blood Thinners and Eye Surgery

A common concern comes up when someone on blood thinners needs cataract surgery or another eye procedure. Should the medication be stopped beforehand? The evidence here is reassuring for the most common operations. In a study comparing cataract surgery patients on direct oral anticoagulants with patients not on any anticoagulant, there was no significant difference in intraoperative or postoperative bleeding rates.¹²

A systematic review and meta-analysis of warfarin patients undergoing cataract surgery did find that continuing warfarin increased the odds of bleeding roughly threefold. But the bleeds were almost entirely minor: small dot-like collections of blood in the front of the eye or subconjunctival hemorrhages on the surface. No patient in the review had compromised visual acuity from a bleeding event.¹³ The consensus among ophthalmologists has shifted toward continuing anticoagulation for cataract surgery rather than stopping it, because the risk of a clot or stroke from temporarily stopping the drug outweighs the risk of a self-limited eye bleed during the procedure.

More invasive eye surgeries, like vitrectomy for a retinal detachment, may call for a different approach. The decision depends on the urgency of the surgery, the specific blood thinner, and the patient’s underlying clotting risk. There is no one-size-fits-all answer, and your ophthalmologist and the doctor managing your anticoagulation should coordinate before any procedure.

Retinal Vein Occlusions and What Blood Thinners Cannot Prevent

Some people assume that because they are taking a blood thinner, they are protected from any clot-related eye problem. That assumption is wrong. Retinal vein occlusion, a condition where a clot or compression blocks a vein draining blood from the retina, can still happen even while on full anticoagulation. A review of the literature spanning over two decades found no protective or preventive benefit of either antiplatelet or anticoagulant therapy against retinal vascular occlusions.¹⁴ An earlier study specifically looking at warfarin users reached the same conclusion: being on warfarin did not preclude retinal vein occlusion, and neither did combining warfarin with aspirin.¹⁵

Retinal vein occlusion typically causes sudden painless blurring or vision loss in one eye. The underlying problem in retinal vein occlusion involves local mechanical and inflammatory factors in the eye’s small vessels that do not respond to systemic anticoagulation the way a deep vein thrombosis in the leg might. Interestingly, once a retinal vein occlusion has already occurred, there is some evidence that anticoagulant therapy may help improve visual outcomes: a meta-analysis found that about 64% of patients treated with anticoagulants after a retinal vein occlusion showed visual improvement, compared with roughly a third of those treated with antiplatelet drugs alone.¹⁶ So the drugs may have a role in treatment but not in prevention, an unintuitive distinction that matters for patient expectations.

When to Call Your Doctor

Knowing which visual symptoms warrant concern and which can wait for your next scheduled visit is genuinely useful if you are on blood thinners. A sudden shower of new floaters, a curtain or shadow moving across your vision, or a sudden overall blurring in one eye could indicate vitreous hemorrhage or retinal detachment, and these need same-day evaluation. Sudden loss of part of your visual field, especially with headache or any other neurological symptom, should prompt an emergency visit because of the possibility of stroke. A painless red patch on the white of the eye, on the other hand, is almost certainly a subconjunctival hemorrhage and usually does not require any treatment beyond waiting for it to clear.

Gradual blurriness that develops over weeks or months is less likely to be related to your blood thinner and more likely to reflect age-related changes like cataracts, dry eye, or shifting prescriptions. Still, if you are on anticoagulation and have AMD or diabetic retinopathy, even gradual changes deserve an ophthalmology visit, because a slow leak might be growing larger without dramatic symptoms. Your eye doctor can look at the retina directly and catch a developing hemorrhage before it expands to the point of causing permanent damage.

1
PubMed. Oral anticoagulation and the risk of vitreous hemorrhage and retinal tears in eyes with acute posterior vitreous detachment
2
JAMA Network Open. Antithrombotic Medications and Intraocular Hemorrhage Risk in Exudative Age-Related Macular Degeneration
3
PubMed Central. Risk of intraocular hemorrhage with new oral anticoagulants
4
PubMed. Risk factors and complications of subconjunctival hemorrhages in patients taking warfarin
5
PubMed Central. Risk of Intraocular Bleeding With Novel Oral Anticoagulants Compared With Warfarin: A Systematic Review and Meta-analysis
6
JAMA Ophthalmology. Association of Novel Oral Antithrombotics With the Risk of Intraocular Bleeding
7
PubMed. Ophthalmic Complications Associated with Direct Oral Anticoagulant Medications
8
American Journal of Ophthalmology. Subretinal Hemorrhages Associated with Age-Related Macular Degeneration in Patients Receiving Anticoagulation or Antiplatelet Therapy
9
BMJ. Blurred vision
10
PubMed Central. Bilateral optic neuropathy related to severe anemia in a patient with alcoholic cirrhosis
11
PubMed. Signal mining for non-bleeding adverse event in novel oral anticoagulants: a pharmacovigilance study based on FAERS database
12
PubMed Central. Effect of direct oral anticoagulants on bleeding during and after cataract surgery
13
PubMed. Safety of continuing warfarin therapy during cataract surgery: a systematic review and meta-analysis
14
PubMed Central. Retinal Vascular Occlusion in Patients on Anticoagulation and Antiplatelet Therapy: a Case Report and Comprehensive Review
15
PubMed. Retinal vein occlusions in patients taking warfarin
16
PubMed. Antithrombotic treatment for retinal vein occlusion: a systematic review and meta-analysis