Neurological Vision Impairment
Neurological vision impairment (NVI) describes vision impairment caused by damage to the brain, including a stroke, tumour, brain injury or degenerative disease.
Vision impairment is generally thought of as damage to or deterioration of the eyes. However, there are many different areas of the brain that interpret what our eyes see. When these areas are damaged, the eyes may still function but the message might be misinterpreted or unable to get through to the brain.
An added complication is that people with brain injuries are not always aware that their vision is impaired. Because their brain is damaged, it may not properly inform them that they can't see properly. This can put the client in potentially dangerous situations.
Neither glasses nor eye surgery will restore sight for these people.
People who have had a stroke will sometimes experience a visual-field deficit called a homonymous hemianopia. This refers to a loss of sight in the same visual field of both eyes - for example, the left half of both eyes.
Functional implications of homonymous hemianopia include:
- Seeing only half an image.
- Bumping into objects on the side of the deficit field of vision.
- Missing half the food on a plate.
- Inadvertently walking past doors and other landmarks.
- Being startled by objects suddenly appearing from the deficit field of vision.
- Misreading street signs.
- Being anxious or uncertain when travelling in crowded areas.
- Having difficulty reading due to problems effectively scanning the page.
Instructors from Guide Dogs NSW/ACT can teach compensatory scanning techniques to alleviate these functional difficulties.
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