Brain Injuries and PressVision
Peripheral Vision Problems
Patients with acquired brain injuries often have difficulty with peripheral vision even though they are still are capable of 20/20 eyesight. The most common example of this is a patient with homonymous hemianopia, meaning that one half of the visual field is missing on either the right or left side.
Visual fields are measured while you place your chin on a chin rest looking straight ahead inside an instrument that looks like a bowl. You’re asked to click a small mouse clicker whenever you think you’ve seen a light off to the side. As you can see here, the top image has a field within normal range for an older adult. The dark spots on either side are the brain’s normal blind spot reference to each eye. The bottom image shows the right half of each field to be dark, therefore this person has a right homonymous hemianopia.
To a person with this condition, the top scene in the photo on the right would appear to look like the one on bottom.
Peripheral vision problems of this nature cause great difficulty in reading, particularly in English.
Our ability to read is directed by saccades, or small eye movements proceeding right to left. A patient with homonymous hemianopia is always moving their eyes toward the blind field, and therefore loses the preview of what is coming next making eye movement patterns uncertain and unstable. Other functions that are disrupted involve orientation and mobility. Patients will veer to the left and may bump into objects on the right side, being unaware of them. Driving becomes a major challenge.
A related but distinct peripheral vision problem is known as neglect or inattention.
This occurs when the visual field is intact, but the patient unintentionally tunes out one side of the body. It can occur with hearing, touch, or vision. A classic example is a patient who eats a meal and leaves food on one side of the plate, thinking that everything is finished. When drawing a clock, all the numbers are squished onto one side, as if the other side doesn’t exist. It is not surprising therefore that patients with visual field loss or inattention have a shift of their midline to the preferred side.
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