Homonymous Hemianopia (Homonymous Hemianopsia)

What is homonymous hemianopia?

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.

What are the most common causes of homonymous hemianopia?

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.
• Transient ischemic attacks (TIAs).
• Brain bleeds (intracranial hemorrhages).

Strokes and TIAs

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.

Brain bleeds

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.

Other conditions that can cause homonymous hemianopia

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:

• Brain infections and inflammation (such as encephalitis or neurosyphilis).
• Brain lesions.
• Brain tumors (including cancer).
• Concussions and traumatic brain injuries (TBIs).
• Degenerative brain diseases like Alzheimer’s disease or Creutzfeldt-Jakob disease (CJD).
• Inflammatory and autoimmune conditions like multiple sclerosis (MS) or neuromyelitis optica (NMO).
• Metabolic conditions or effects, like low blood sugar (hypoglycemia).
• Migraines (especially migraines with auras).
• Seizures and epilepsy.

How is homonymous hemianopia treated?

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:

• Ischemic stroke or TIA: The main treatments for ischemic stroke restore blood flow with medications, like anticoagulants or clot-busting (thrombolytic) drugs, or specific medical procedures like thrombectomy.
• Brain bleeds and hemorrhagic stroke: Treatments usually involve surgery (like craniectomy or craniotomy) to relieve pressure inside your skull and repair the affected blood vessel, if possible.
• Migraines: Treatments usually include preventive medications that keep migraines from happening or abortive (“rescue”) medications to stop them when they happen. Dozens of medications fall into one or both of those categories.
• Seizures and epilepsy: Antiseizure medications can stop seizures, prevent them or both. Epilepsy surgery is also an option if medications aren’t effective or helpful.

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.

Can homonymous hemianopia be prevented?

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:

• See a healthcare provider for an annual physical or checkup to improve the odds of early detection of conditions that could cause HH.
• Wear safety gear like helmets and seatbelts to reduce the risk of head injuries.
• Reach and maintain a weight that’s healthy for you to prevent or delay a stroke or similar conditions.
• Manage chronic conditions to prevent issues or events that could cause HH, like taking epilepsy medicine to prevent seizures or anticoagulants to prevent clots that could cause a stroke.

When should homonymous hemianopia be treated by a doctor or healthcare provider?

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.

What does homonymous hemianopia look like?

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:

• Negative symptoms (loss or decrease in ability). If the effect from homonymous hemianopia is negative, you might have dimmed vision or half of your visual field looks dark or blacked out. These symptoms usually mean the affected area isn’t working as well as it should or at all.
• Positive symptoms (new or additional effect). Positive symptoms of HH can look like a bright fog or haze, distortions or flashes in the affected part of your vision. These symptoms usually indicate the affected area is still working, but it’s malfunctioning, like with a seizure or migraine.

What can I do to help myself manage long-term homonymous hemianopia?

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:

• Use a straight edge (like a bookmark or ruler) to direct your eyes to the next line of text.
• Work on willingly increasing the size of small eye movements as you read words along each line of text. You want to “capture” each word in your field of vision and recognize it as a whole word before reading it.
• Place your hand at the edge of the page so it’s easy to tell where the margins are.
• Hold the text at a 45-degree to 90-degree angle so that you read vertically instead of horizontally. If your vision loss is on the right, you should read downward. If it’s on the left, you should read upward. Reading in a specific direction keeps the next line of text in your field of vision.

Strategies to improve navigating the world around you include:

• When walking or moving around, learn to direct your eyes toward the good side of your visual field.
• When walking into a new environment, pause and rotate your head to scan the area through the good part of your field of vision. Observe where objects and people are, and mentally recreate a picture of what you see. Practicing this, particularly within the first six months after vision loss, can help train your brain so you do this automatically.
• When looking for objects that might be in the missing area of your vision, consciously make large eye movements to that side and then let your eyes come back to the object.
• When walking, let a partner walk on the blind side and provide their arm for guidance.
• When you’re in group situations, try to stand or angle yourself so people are visible in your working visual field as much as possible.
• When in a theater, sit as far as you can on the same side as the missing area of your visual field. That maximizes how much of the action stays where it’s easier for you to see it.
• Play real-life (not computer-based) card games and do crossword puzzles to regain and improve hand-eye coordination.
• Do word search or picture search puzzles to improve eye scanning at near distances.

Other treatments or techniques your provider might recommend include:

• Prisms on glasses (either integrated into the lenses or in special lens attachments) may help expand the center of your vision. Prisms change how objects appear, which can help you compensate for the missing area of your vision.
• Driving is hazardous for many people with homonymous hemianopsia, particularly if you have other brain-related issues or symptoms. Talk to your provider about whether you can and should drive. You may also need to practice on a driving simulator or pass a test with an instructor, who’ll determine if you can still drive safely.
• Some makers of computer-assisted programs claim to promote recovery of your entire field of vision. But not all these claims are accurate, and these programs can be expensive. Talk to your healthcare provider or specialist about whether these programs are legitimate or where you can find programs that can help.

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.