Hemianopia, sometimes called hemianopsia, is partial blindness or a loss of sight in half of your visual field. It’s caused by brain damage, rather than a problem with your eyes.

Depending on the cause, hemianopia may be permanent or temporary. Read on to learn more about the different types of hemianopia and how they’re treated.

There are a few types of hemianopia, depending on the parts of the brain involved.

Your brain contains two halves:

  • Left side. This half receives information from both eyes, processes it, and sends signals that allow you to see the right side of your visual world.
  • Right side. This half receives information from both eyes, processes it, and sends signals that allow you to see the left side of your visual world.

These signals are carried through optic nerves, which cross over and connect in an area called the optic chiasm.

Damage to either side of the brain or these nerve pathways can cause different types of hemianopia:

  • Homonymous hemianopia. This type affects the same side of each eye. For example, you might only be able to see out of the right half of each of your eyes.
  • Heteronymous hemianopia. This type affects different sides of each eye. For example, you might only be able to see out the left side of your right eye and the right side of your left eye.

The main symptom of hemianopia is losing half of your visual field in one or both eyes. But it can also cause a range of other symptoms, including:

  • distorted sight
  • double vision
  • difficulty understanding what you’re seeing
  • vision that appears dimmed
  • decreased night vision
  • moving the body or head away from the affected side
  • visual hallucinations

For many people with hemianopia, their symptoms become more noticeable when they try to read or focus their eyes on something.

The most common cause of homonymous hemianopia is stroke.

However, any type of damage to your optic nerves or brain can lead to hemianopia. Common causes of these types of damage include:

Hemianopia is usually first detected during a routine eye exam that includes a visual field exam. This will help your doctor determine how well your eyes can focus on specific objects.

Depending on the results of your exam, your doctor might also take a look at the back of your eye with imaging tests. They may also shoot short bursts of air into your eyes to check the pressure within your eyes. These tests will help your doctor rule out other possible causes of your vision problem.

Remember, hemianopia originates in your brain, not your eyes. Ruling out any issues with your eyes will help your doctor reach a diagnosis.

Depending on your other symptoms, your doctor might also order a brain scan and a complete blood count test to check for signs of brain damage.

Treatment for hemianopia depends on the cause. Cases caused by a stroke or head injury might resolve on their own after a few months.

If you have hemianopia due to a brain tumor, your vision may return after you start taking medication or have surgery to remove or shrink the tumor.

In some cases, hemianopia never resolves. However, there are several things you can do to help improve your vision, including:

  • wearing prismatic correction glasses to help with double vision
  • getting vision compensatory training to help you use your remaining vision more efficiently
  • undergoing vision restoration therapy to improve visual information processing

Hemianopia can be a frustrating condition because it often makes everyday things, such as reading or walking, difficult.

In some cases, hemianopia resolves on its own within a few months. While hemianopia can be permanent, several treatment options can help you adapt to reduced vision.

Work with your doctor to figure out the best treatment plan to help improve your vision. You can also check out these resources for people with low vision from the American Academy of Ophthalmology.