Hemianopsia is a loss of vision in half of the visual field of one eye or both eyes. Common causes are stroke, brain tumor, and trauma to the brain.
Normally, the left half of the brain receives vision from the right eye, and vice versa.
Information from the 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 one visual field.
Hemianopsia can occur when there is damage to the optic nerves, optic chiasm, or visual processing regions of the brain.
The most common causes of brain damage that can result in hemianopsia are:
- traumatic head injuries
Less commonly, brain damage can also be caused by:
- exposure to toxins
- neurodegenerative disorders
- transient events, such as seizures or migraines
A person with hemianopsia can see only part of the visual field of each eye. Hemianopsia is classified by the part of the visual field that is 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
Especially in cases of partial hemianopsia, symptoms can be easily confused with those of other disorders. If you suspect you may have hemianopsia, see your doctor. If hemianopsia occurs quickly or suddenly, see your doctor immediately.
Symptoms may include:
- sensation that something is wrong with your vision
- bumping into objects while walking, especially doorframes 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
- difficulty finding objects or reaching for objects on desks and countertops, or in cabinets and closets
Hemianopsia can be detected by a visual field test. The patient focuses on a single point on a screen while lights are shown above, below, to the left, and to the right of center. By determining which lights the patient can see, the test maps out the specific part of the patient’s visual field that has been damaged.
If part of a patient’s visual field is impaired, a magnetic resonance imaging (MRI) scan is most often suggested. The scan can show whether there is brain damage to the areas controlling vision.
Treatment addresses the condition causing hemianopsia. In some causes, the hemianopsia may improve over time. Where brain damage has occurred, the hemianopsia is usually permanent, but it can be helped by a number of 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 the brain to grow new connections around the damaged areas to restore lost functions. It can restore as much as five degrees of the lost visual field (Goodrich 2010).
Visual Field Expander Aid
Special glasses can be fitted with a prism in each lens. These prisms bend incoming light so that it reaches the non-damaged section of the visual field.
Scanning Therapy (Saccadic Eye Movement Training)
Scanning therapy teaches patients to develop the habit of moving their eyes to look in the portion of the visual field that they normally cannot see. Turning the head also widens the available field of vision. By developing the habit, a person with hemianopsia will eventually learn to always look with the visual field that is still intact.
A number of strategies can make reading less challenging. People with hemianopsia 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 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 the unaffected side. This will maximize the amount of the screen that can be seen.
- The ability to drive will vary from person to person. A driving simulator or consultation with a doctor can ascertain safety.