Homonymous hemianopia is vision loss on the same side, left or right, in both eyes. It happens with conditions that affect your brain. It’s always a medical emergency when you have it for the first time. A specialist or provider can guide you on what to do if you have a condition that could cause it.
Homonymous hemianopia (also known as homonymous hemianopsia or HH) is a symptom that makes you see only one side ― right or left ― of the visual field of each of your eyes. “Homonymous” in this context means “the same side of both eyes,” and “hemianopia” (sometimes spelled “hemianopsia”) means “half vision loss.”
Your visual field is everything you see when your eyes are open. When your vision works correctly, everything on the right side of your visual field goes to the left side of your brain, and everything on the left side goes to the right side of your brain. Your visual system has a special setup to make that happen.
Each optic nerve carries visual information from both sides until they reach a point in your brain called the optic chiasm (pronounced “KY-azm”). Once the nerve fibers get there, some of the fibers change directions. Nerve fibers from both eyes that handle the left side of your vision go to the right side of your brain and vice versa.
HH affects signals from the same side of both eyes traveling together after passing the chiasm. That’s why HH causes vision loss on the same side of both eyes. Experts classify it as a visual field defect, and the conditions that cause it all affect your brain. It’s usually sudden, but some conditions can make it develop more gradually.
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HH means something is disrupting your visual system on one side of your brain. Between 42% and 89% of HH cases happen because of these three life-threatening emergency conditions:
Strokes happen when something disrupts blood flow to part of your brain. Without blood flow, the affected brain areas stop working correctly and start dying. When this is severe or lasts too long, it causes permanent brain damage. These can happen because of a blockage (ischemic stroke) or bleeding (hemorrhagic stroke).
People often call TIAs “mini-strokes,” but they aren’t necessarily smaller. They’re like an ischemic stroke, but the symptoms are temporary (they usually stop if you sit down or rest). But having a TIA greatly increases your risk of having a stroke within the next few days. That’s why a TIA is also a medical emergency, just like a stroke.
Bleeding inside your brain is dangerous because the blood has nowhere to go. Over time, the buildup of blood can press on and damage your brain.
Many other brain conditions can also cause HH when they damage vision-related areas. Some of these conditions are dangerous or life-threatening. Others are relatively minor, and the risk of permanent damage is minimal.
Examples of other conditions that can cause HH include:
The treatments for HH vary widely depending on the underlying cause. Some examples of treatment options for specific conditions that can cause homonymous hemianopia include:
Something to remember is that treatments that work for one cause may not work for others, or they could do more damage. Because there are so many treatment options and other factors in play, your healthcare provider is the best person to tell you about the treatment options for your specific case.
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HH is impossible to prevent, and it happens unpredictably. But you can reduce your risk of having some of the conditions that cause it if you take the following steps:
If you’ve never experienced homonymous hemianopsia before, you should react like it’s a medical emergency. HH is most likely a symptom of a life-threatening emergency condition like a stroke or brain bleed.
The best and safest course of action is to call 911 (or your local emergency services number) immediately. You shouldn’t try to drive yourself to get medical care because the loss or disruption in your vision can make driving dangerous to yourself and others.
If you’ve experienced HH before and have a diagnosed condition that can cause it, how you respond can vary slightly. You should ask your healthcare provider what to do if you have it again. They can give you more specific guidance on when this symptom needs immediate medical attention.
But when in doubt, the safest thing to do is to get medical attention. Many conditions that cause HH are time-sensitive, and seconds can make a huge difference.
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Hemianopia affects one side of your visual field, left or right, in both eyes at the same time. It can be hard to tell that it’s affecting both eyes at the same time unless you specifically test your vision one eye at a time (a healthcare provider usually tests for this as part of a physical exam, but you may also notice it yourself).
Healthcare providers often describe the symptoms as “positive” or “negative.” That doesn’t mean good and bad in this context. Instead, it can mean the following:
If HH is likely to be a long-term or permanent issue for you, there are many things you can do to help yourself adapt to the condition or compensate for it. A low-vision specialist or visual rehabilitation provider can guide you through specific exercises and approaches.
Strategies to improve reading ability include:
Strategies to improve navigating the world around you include:
Other treatments or techniques your provider might recommend include:
A note from Cleveland Clinic
It’s understandable if you feel scared or confused if you can suddenly see only half of the world in front of you. Homonymous hemianopia can signal severe, even dangerous conditions. That’s why it’s important to act to take care of yourself.
If you’ve never experienced this before, get emergency medical care immediately by calling 911 or your local emergency services number. If you have a condition that can cause this symptom, the healthcare provider who diagnosed you can guide you on how to react. And when in doubt, get medical care right away. Many conditions that cause this are reversible if you act quickly.
Last reviewed on 01/09/2024.
Learn more about the Health Library and our editorial process.
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Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy