Hemianopsia is a loss of vision in half of your visual field of one eye or both eyes. Common causes are:
- brain tumor
- trauma to the brain
Normally, the left half of your brain receives visual information from the right side of both eyes, and vice versa.
Some information from your optic nerves crosses to the other half of the brain using an X-shaped structure called the optic chiasm. When any part of this system is damaged, the result can be partial or complete loss of vision in the visual field.
Hemianopsia can occur when there’s damage to the:
- optic nerves
- optic chiasm
- visual processing regions of the brain
The most common causes of brain damage that can result in hemianopsia are:
Less commonly, brain damage can also be caused by:
- exposure to toxins
- neurodegenerative disorders
- transient events, such as seizures or migraines
With hemianopsia, you can see only part of the visual field for each eye. Hemianopsia is classified by the part of your visual field that’s missing:
- bitemporal: outer half of each visual field
- homonymous: the same half of each visual field
- right homonymous: right half of each visual field
- left homonymous: left half of each visual field
- superior: upper half of each visual field
- inferior: lower half of each visual field
Symptoms can be easily confused with those of other disorders, especially in cases of partial hemianopsia. If you suspect you may have hemianopsia, see your healthcare provider. If hemianopsia occurs quickly or suddenly, seek medical attention immediately.
Symptoms may include:
- sensation that something is wrong with your vision
- bumping into objects while walking, especially door frames and people
- difficulty driving, especially when changing lanes or avoiding objects on the side of the road
- frequently losing your place while reading or having trouble finding the start or end of a line of a text
- difficulty finding or reaching for objects on desks or countertops or in cabinets and closets
Hemianopsia can be detected by a visual field test. You focus on a single point on a screen while lights are shown above, below, to the left, and to the right of center of that focal point.
By determining which lights you can see, the test maps out the specific part of your visual field that has been damaged.
If part of your visual field is impaired, an MRI scan is often suggested. The scan can show whether there’s brain damage to the areas of the brain responsible for vision.
Your doctor will prescribe a treatment that addresses the condition causing your hemianopsia. In some cases, hemianopsia may improve over time. Where brain damage has occurred, hemianopsia is usually permanent, but it can be helped by a few therapies.
The degree of function that can be restored depends on the cause and severity of the damage.
Vision restoration therapy (VRT)
VRT works by repeatedly stimulating the edges of the missing field of vision. The adult brain has some ability to rewire itself. VRT causes your brain to grow new connections around the damaged areas to restore lost functions.
It has been found to restore as much as 5 degrees of lost visual field in some individuals.
Visual field expander aid
Special glasses can be fitted for you with a prism in each lens. These prisms bend incoming light so that it reaches the non-damaged section of your visual field.
Scanning therapy (saccadic eye movement training)
Scanning therapy teaches you to develop the habit of moving your eyes to look in the portion of the visual field that you normally cannot see. Turning your head also widens your available field of vision.
By developing this habit, you’ll eventually learn to always look with the visual field that’s still intact.
A number of strategies can make reading less challenging. You can look for long words to use as reference points. A ruler or sticky note can mark the beginning or end of the text. Some people also benefit by turning their text sideways.
If you have hemianopsia, making a few lifestyle changes can help:
- When walking with another person, place that person on the affected side. Having a person there will prevent you from bumping into objects outside of your field of vision.
- In a movie theater, sit toward the affected side, so that the screen is largely on your unaffected side. This will maximize the amount of the screen that you can see.
- The ability to drive will vary from person to person. A driving simulator or consultation with a healthcare provider can help you determine safety.