What is homonymous hemianopsia?
Homonymous hemianopsia is a condition in which a person sees only one side―right or left―of the visual world of each eye. The person may not be aware that the vision loss is happening in both eyes, not just one.
Under normal circumstances, the left half of the brain processes visual information from both eyes about the right side of the world. The right side of the brain processes visual information from both eyes about the left side of the world.
A visual world of someone with normal vision
In homonymous hemianopsia, an injury to the left part of the brain results in the loss of the right half of the visual world of each eye. An injury to the right part of the brain produces loss of the left side of the visual world of each eye.
This condition is created by a problem in brain function rather than a disorder of the eyes themselves.
A visual world of someone with homonymous hemianopsia
What causes homonymous hemianopsia?
The most common cause of this type of vision loss is stroke. However, any disorder that affects the brain—including tumors, inflammation, and injuries--can be a cause.
It is estimated that 70% of the injuries leading to hemianopsias are due to an obstruction (blockage) of the blood supply (stroke). Fifteen percent are due to tumors, and 5% are due to bleeding in the brain. Males from the ages of 50 to 70 are most frequently affected. This population is the group most likely to have diseases that affect the circulatory system.
As for the areas of the brain most affected, 40% of homonymous hemianopsias originate in the occipital (rear) lobe of the cerebral hemisphere. A total of 30% originate in the parietal (middle) lobe, 25% in the temporal (lower) lobe, and 5% in the optic tract and lateral geniculate nucleus (pathways of the optic nerves connecting the eyes to the brain).
What are the symptoms of homonymous hemianopsia?
- Bumping into or failing to notice things on the side of the hemianopsia. This can make such everyday tasks as crossing the street or driving a car unsafe.
- Missing parts of words or parts of an eye chart on the side of the hemianopsia when reading.
- Not noticing objects on a desk or table, or even food on a plate to the side of the hemianopsia.
- Frustration with reading because it is difficult for the eyes to pick up the beginning of the next line.
- Tendency to turn the head or body away from the side of the hemianopsia.
- Drifting in a direction away from the hemianopsia when walking.
- Visual hallucinations that appear in the form of lights, shapes, or geometric figures or as the image of a recognizable object. Sometimes a movement noted on the normal side of vision is believed to be also seen at the same time on the side of the visual loss.
Note: There is no correlation between homonymous hemianopsia and nearsightedness or farsightnedness. These conditions are not related.